Patchwork [v6,4/4] Add support for net bridge

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Submitter Corey Bryant
Date Dec. 19, 2011, 1:11 p.m.
Message ID <1324300318-3419-5-git-send-email-coreyb@linux.vnet.ibm.com>
Download mbox | patch
Permalink /patch/132226/
State New
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Comments

Corey Bryant - Dec. 19, 2011, 1:11 p.m.
The most common use of -net tap is to connect a tap device to a bridge.  This
requires the use of a script and running qemu as root in order to allocate a
tap device to pass to the script.

This model is great for portability and flexibility but it's incredibly
Anthony Liguori - Dec. 19, 2011, 7:36 p.m.
On 12/19/2011 07:11 AM, Corey Bryant wrote:
> The most common use of -net tap is to connect a tap device to a bridge.  This
> requires the use of a script and running qemu as root in order to allocate a
> tap device to pass to the script.
>
> This model is great for portability and flexibility but it's incredibly
> difficult to eliminate the need to run qemu as root.  The only really viable
> mechanism is to use tunctl to create a tap device, attach it to a bridge as
> root, and then hand that tap device to qemu.  The problem with this mechanism
> is that it requires administrator intervention whenever a user wants to create
> a guest.
>
> By essentially writing a helper that implements the most common qemu-ifup
> script that can be safely given cap_net_admin, we can dramatically simplify
> things for non-privileged users.  We still support existing -net tap options
> as a mechanism for advanced users and backwards compatibility.
>
> Currently, this is very Linux centric but there's really no reason why it
> couldn't be extended for other Unixes.
>
> A typical invocation would be similar to one of the following:
>
>    qemu linux.img -net bridge -net nic,model=virtio
>
>    qemu linux.img -net tap,helper=/usr/local/libexec/qemu-bridge-helper
>                   -net nic,model=virtio
>
>    qemu linux.img -netdev bridge,id=hn0
>                   -device virtio-net-pci,netdev=hn0,id=nic1
>
>    qemu linux.img -netdev tap,helper=/usr/local/libexec/qemu-bridge-helper,id=hn0
>                   -device virtio-net-pci,netdev=hn0,id=nic1
>
> The default bridge that we attach to is br0.  The thinking is that a distro
> could preconfigure such an interface to allow out-of-the-box bridged networking.
>
> Alternatively, if a user wants to use a different bridge, a typical invocation
> would be simliar to one of the following:
>
>    qemu linux.img -net bridge,br=qemubr0 -net nic,model=virtio
>
>    qemu linux.img -net tap,helper=/usr/local/libexec/qemu-bridge-helper,br=qemubr0
>                   -net nic,model=virtio
>
>    qemu linux.img -netdev bridge,br=qemubr0,id=hn0
>                   -device virtio-net-pci,netdev=hn0,id=nic1
>
>    qemu linux.img -netdev tap,helper=/usr/local/libexec/qemu-bridge-helper,br=qemubr0,id=hn0
>                   -device virtio-net-pci,netdev=hn0,id=nic1
>
> Signed-off-by: Anthony Liguori<aliguori@us.ibm.com>
> Signed-off-by: Richa Marwaha<rmarwah@linux.vnet.ibm.com>
> Signed-off-by: Corey Bryant<coreyb@linux.vnet.ibm.com>
> ---
>   configure       |    2 +
>   net.c           |   29 ++++++++-
>   net.h           |    3 +
>   net/tap.c       |  187 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>   net/tap.h       |    3 +
>   qemu-options.hx |   74 ++++++++++++++++++----
>   6 files changed, 281 insertions(+), 17 deletions(-)
>
> diff --git a/configure b/configure
> index 6ed4196..4839694 100755
> --- a/configure
> +++ b/configure
> @@ -2905,6 +2905,8 @@ echo "sysconfdir=$sysconfdir">>  $config_host_mak
>   echo "docdir=$docdir">>  $config_host_mak
>   echo "confdir=$confdir">>  $config_host_mak
>   echo "libexecdir=\${prefix}/libexec">>  $config_host_mak
> +echo "CONFIG_QEMU_SHAREDIR=\"$prefix$datasuffix\"">>  $config_host_mak
> +echo "CONFIG_QEMU_HELPERDIR=\"$prefix/libexec\"">>  $config_host_mak
>
>   case "$cpu" in
>     i386|x86_64|alpha|arm|cris|hppa|ia64|lm32|m68k|microblaze|mips|mips64|ppc|ppc64|s390|s390x|sparc|sparc64|unicore32)
> diff --git a/net.c b/net.c
> index f7bebf8..9296224 100644
> --- a/net.c
> +++ b/net.c
> @@ -952,6 +952,14 @@ static const struct {
>                   .type = QEMU_OPT_STRING,
>                   .help = "script to shut down the interface",
>               }, {
> +                .name = "br",
> +                .type = QEMU_OPT_STRING,
> +                .help = "bridge name",
> +            }, {

I don't think passing br= makes a whole of sense for -net tap.  I think it would 
make more sense to make sure that helper could take a shell string so you could do:

-netdev tap,helper="/usr/libexec/qemu-bridge-helper --br=br0"

Regards,

Anthony Liguori

> +                .name = "helper",
> +                .type = QEMU_OPT_STRING,
> +                .help = "command to execute to configure bridge",
> +            }, {
>                   .name = "sndbuf",
>                   .type = QEMU_OPT_SIZE,
>                   .help = "send buffer limit"
> @@ -1049,6 +1057,23 @@ static const struct {
>               { /* end of list */ }
>           },
>       },
> +    [NET_CLIENT_TYPE_BRIDGE] = {
> +        .type = "bridge",
> +        .init = net_init_bridge,
> +        .desc = {
> +            NET_COMMON_PARAMS_DESC,
> +            {
> +                .name = "br",
> +                .type = QEMU_OPT_STRING,
> +                .help = "bridge name",
> +            }, {
> +                .name = "helper",
> +                .type = QEMU_OPT_STRING,
> +                .help = "command to execute to configure bridge",
> +            },
> +            { /* end of list */ }
> +        },
> +    },
>   };
>
>   int net_client_init(Monitor *mon, QemuOpts *opts, int is_netdev)
> @@ -1071,7 +1096,8 @@ int net_client_init(Monitor *mon, QemuOpts *opts, int is_netdev)
>   #ifdef CONFIG_VDE
>               strcmp(type, "vde") != 0&&
>   #endif
> -            strcmp(type, "socket") != 0) {
> +            strcmp(type, "socket") != 0&&
> +            strcmp(type, "bridge") != 0) {
>               qerror_report(QERR_INVALID_PARAMETER_VALUE, "type",
>                             "a netdev backend type");
>               return -1;
> @@ -1141,6 +1167,7 @@ static int net_host_check_device(const char *device)
>   #ifdef CONFIG_VDE
>                                          ,"vde"
>   #endif
> +                                       , "bridge"
>       };
>       for (i = 0; i<  sizeof(valid_param_list) / sizeof(char *); i++) {
>           if (!strncmp(valid_param_list[i], device,
> diff --git a/net.h b/net.h
> index c6b4190..0fd7e23 100644
> --- a/net.h
> +++ b/net.h
> @@ -36,6 +36,7 @@ typedef enum {
>       NET_CLIENT_TYPE_SOCKET,
>       NET_CLIENT_TYPE_VDE,
>       NET_CLIENT_TYPE_DUMP,
> +    NET_CLIENT_TYPE_BRIDGE,
>
>       NET_CLIENT_TYPE_MAX
>   } net_client_type;
> @@ -173,6 +174,8 @@ int do_netdev_del(Monitor *mon, const QDict *qdict, QObject **ret_data);
>
>   #define DEFAULT_NETWORK_SCRIPT "/etc/qemu-ifup"
>   #define DEFAULT_NETWORK_DOWN_SCRIPT "/etc/qemu-ifdown"
> +#define DEFAULT_BRIDGE_HELPER CONFIG_QEMU_HELPERDIR "/qemu-bridge-helper"
> +#define DEFAULT_BRIDGE_INTERFACE "br0"
>
>   void qdev_set_nic_properties(DeviceState *dev, NICInfo *nd);
>
> diff --git a/net/tap.c b/net/tap.c
> index 6c27a94..b2b82a1 100644
> --- a/net/tap.c
> +++ b/net/tap.c
> @@ -382,6 +382,143 @@ static int launch_script(const char *setup_script, const char *ifname, int fd)
>       return -1;
>   }
>
> +static int recv_fd(int c)
> +{
> +    int fd;
> +    uint8_t msgbuf[CMSG_SPACE(sizeof(fd))];
> +    struct msghdr msg = {
> +        .msg_control = msgbuf,
> +        .msg_controllen = sizeof(msgbuf),
> +    };
> +    struct cmsghdr *cmsg;
> +    struct iovec iov;
> +    uint8_t req[1];
> +    ssize_t len;
> +
> +    cmsg = CMSG_FIRSTHDR(&msg);
> +    cmsg->cmsg_level = SOL_SOCKET;
> +    cmsg->cmsg_type = SCM_RIGHTS;
> +    cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
> +    msg.msg_controllen = cmsg->cmsg_len;
> +
> +    iov.iov_base = req;
> +    iov.iov_len = sizeof(req);
> +
> +    msg.msg_iov =&iov;
> +    msg.msg_iovlen = 1;
> +
> +    len = recvmsg(c,&msg, 0);
> +    if (len>  0) {
> +        memcpy(&fd, CMSG_DATA(cmsg), sizeof(fd));
> +        return fd;
> +    }
> +
> +    return len;
> +}
> +
> +static int net_bridge_run_helper(const char *helper, const char *bridge)
> +{
> +    sigset_t oldmask, mask;
> +    int pid, status;
> +    char *args[5];
> +    char **parg;
> +    int sv[2];
> +
> +    sigemptyset(&mask);
> +    sigaddset(&mask, SIGCHLD);
> +    sigprocmask(SIG_BLOCK,&mask,&oldmask);
> +
> +    if (socketpair(PF_UNIX, SOCK_STREAM, 0, sv) == -1) {
> +        return -1;
> +    }
> +
> +    /* try to launch bridge helper */
> +    pid = fork();
> +    if (pid == 0) {
> +        int open_max = sysconf(_SC_OPEN_MAX), i;
> +        char buf[32];
> +
> +        snprintf(buf, sizeof(buf), "%d", sv[1]);
> +
> +        for (i = 0; i<  open_max; i++) {
> +            if (i != STDIN_FILENO&&
> +                i != STDOUT_FILENO&&
> +                i != STDERR_FILENO&&
> +                i != sv[1]) {
> +                close(i);
> +            }
> +        }
> +        parg = args;
> +        *parg++ = (char *)helper;
> +        *parg++ = (char *)"--use-vnet";
> +        *parg++ = (char *)bridge;
> +        *parg++ = buf;
> +        *parg++ = NULL;
> +        execv(helper, args);
> +        _exit(1);
> +    } else if (pid>  0) {
> +        int fd;
> +
> +        close(sv[1]);
> +
> +        do {
> +            fd = recv_fd(sv[0]);
> +        } while (fd == -1&&  errno == EINTR);
> +
> +        close(sv[0]);
> +
> +        while (waitpid(pid,&status, 0) != pid) {
> +            /* loop */
> +        }
> +        sigprocmask(SIG_SETMASK,&oldmask, NULL);
> +        if (fd<  0) {
> +            fprintf(stderr, "failed to recv file descriptor\n");
> +            return -1;
> +        }
> +
> +        if (WIFEXITED(status)&&  WEXITSTATUS(status) == 0) {
> +            return fd;
> +        }
> +    }
> +    fprintf(stderr, "failed to launch bridge helper\n");
> +    return -1;
> +}
> +
> +int net_init_bridge(QemuOpts *opts, Monitor *mon, const char *name,
> +                    VLANState *vlan)
> +{
> +    TAPState *s;
> +    int fd, vnet_hdr;
> +
> +    if (!qemu_opt_get(opts, "br")) {
> +        qemu_opt_set(opts, "br", DEFAULT_BRIDGE_INTERFACE);
> +    }
> +    if (!qemu_opt_get(opts, "helper")) {
> +        qemu_opt_set(opts, "helper", DEFAULT_BRIDGE_HELPER);
> +    }
> +
> +    fd = net_bridge_run_helper(qemu_opt_get(opts, "helper"),
> +                               qemu_opt_get(opts, "br"));
> +    if (fd == -1) {
> +        return -1;
> +    }
> +
> +    fcntl(fd, F_SETFL, O_NONBLOCK);
> +
> +    vnet_hdr = tap_probe_vnet_hdr(fd);
> +
> +    s = net_tap_fd_init(vlan, "bridge", name, fd, vnet_hdr);
> +    if (!s) {
> +        close(fd);
> +        return -1;
> +    }
> +
> +    snprintf(s->nc.info_str, sizeof(s->nc.info_str),
> +             "br=%s", qemu_opt_get(opts, "br"));
> +
> +    return 0;
> +}
> +
>   static int net_tap_init(QemuOpts *opts, int *vnet_hdr)
>   {
>       int fd, vnet_hdr_required;
> @@ -422,13 +559,17 @@ int net_init_tap(QemuOpts *opts, Monitor *mon, const char *name, VLANState *vlan
>   {
>       TAPState *s;
>       int fd, vnet_hdr = 0;
> +    const char *model;
>
>       if (qemu_opt_get(opts, "fd")) {
>           if (qemu_opt_get(opts, "ifname") ||
>               qemu_opt_get(opts, "script") ||
>               qemu_opt_get(opts, "downscript") ||
> -            qemu_opt_get(opts, "vnet_hdr")) {
> -            error_report("ifname=, script=, downscript= and vnet_hdr= is invalid with fd=");
> +            qemu_opt_get(opts, "vnet_hdr") ||
> +            qemu_opt_get(opts, "br") ||
> +            qemu_opt_get(opts, "helper")) {
> +            error_report("ifname=, script=, downscript=, vnet_hdr=, "
> +                         "br= and helper= are invalid with fd=");
>               return -1;
>           }
>
> @@ -440,7 +581,41 @@ int net_init_tap(QemuOpts *opts, Monitor *mon, const char *name, VLANState *vlan
>           fcntl(fd, F_SETFL, O_NONBLOCK);
>
>           vnet_hdr = tap_probe_vnet_hdr(fd);
> +
> +        model = "tap";
> +
> +    } else if (qemu_opt_get(opts, "helper")) {
> +        if (qemu_opt_get(opts, "ifname") ||
> +            qemu_opt_get(opts, "script") ||
> +            qemu_opt_get(opts, "downscript") ||
> +            qemu_opt_get(opts, "vnet_hdr")) {
> +            error_report("ifname=, script=, downscript=, and vnet_hdr= "
> +                         "are invalid with helper=");
> +            return -1;
> +        }
> +
> +        if (!qemu_opt_get(opts, "br")) {
> +            qemu_opt_set(opts, "br", DEFAULT_BRIDGE_INTERFACE);
> +        }
> +
> +        fd = net_bridge_run_helper(qemu_opt_get(opts, "helper"),
> +                                   qemu_opt_get(opts, "br"));
> +        if (fd == -1) {
> +            return -1;
> +        }
> +
> +        fcntl(fd, F_SETFL, O_NONBLOCK);
> +
> +        vnet_hdr = tap_probe_vnet_hdr(fd);
> +
> +        model = "bridge";
> +
>       } else {
> +        if (qemu_opt_get(opts, "br")) {
> +            error_report("br= is invalid with script=");
> +            return -1;
> +        }
> +
>           if (!qemu_opt_get(opts, "script")) {
>               qemu_opt_set(opts, "script", DEFAULT_NETWORK_SCRIPT);
>           }
> @@ -453,9 +628,11 @@ int net_init_tap(QemuOpts *opts, Monitor *mon, const char *name, VLANState *vlan
>           if (fd == -1) {
>               return -1;
>           }
> +
> +        model = "tap";
>       }
>
> -    s = net_tap_fd_init(vlan, "tap", name, fd, vnet_hdr);
> +    s = net_tap_fd_init(vlan, model, name, fd, vnet_hdr);
>       if (!s) {
>           close(fd);
>           return -1;
> @@ -467,6 +644,10 @@ int net_init_tap(QemuOpts *opts, Monitor *mon, const char *name, VLANState *vlan
>
>       if (qemu_opt_get(opts, "fd")) {
>           snprintf(s->nc.info_str, sizeof(s->nc.info_str), "fd=%d", fd);
> +    } else if (qemu_opt_get(opts, "helper")) {
> +        snprintf(s->nc.info_str, sizeof(s->nc.info_str),
> +                "helper=%s,br=%s", qemu_opt_get(opts, "helper"),
> +                qemu_opt_get(opts, "br"));
>       } else {
>           const char *ifname, *script, *downscript;
>
> diff --git a/net/tap.h b/net/tap.h
> index e44bd2b..56c591f 100644
> --- a/net/tap.h
> +++ b/net/tap.h
> @@ -57,4 +57,7 @@ int tap_get_fd(VLANClientState *vc);
>   struct vhost_net;
>   struct vhost_net *tap_get_vhost_net(VLANClientState *vc);
>
> +int net_init_bridge(QemuOpts *opts, Monitor *mon, const char *name,
> +                    VLANState *vlan);
> +
>   #endif /* QEMU_NET_TAP_H */
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 087a3b9..4f2385d 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -1205,11 +1205,14 @@ DEF("net", HAS_ARG, QEMU_OPTION_net,
>       "-net tap[,vlan=n][,name=str],ifname=name\n"
>       "                connect the host TAP network interface to VLAN 'n'\n"
>   #else
> -    "-net tap[,vlan=n][,name=str][,fd=h][,ifname=name][,script=file][,downscript=dfile][,sndbuf=nbytes][,vnet_hdr=on|off][,vhost=on|off][,vhostfd=h][,vhostforce=on|off]\n"
> -    "                connect the host TAP network interface to VLAN 'n' and use the\n"
> -    "                network scripts 'file' (default=" DEFAULT_NETWORK_SCRIPT ")\n"
> -    "                and 'dfile' (default=" DEFAULT_NETWORK_DOWN_SCRIPT ")\n"
> +    "-net tap[,vlan=n][,name=str][,fd=h][,ifname=name][,script=file][,downscript=dfile][,br=bridge][,helper=helper][,sndbuf=nbytes][,vnet_hdr=on|off][,vhost=on|off][,vhostfd=h][,vhostforce=on|off]\n"
> +    "                connect the host TAP network interface to VLAN 'n' \n"
> +    "                use network scripts 'file' (default=" DEFAULT_NETWORK_SCRIPT ")\n"
> +    "                to configure it and 'dfile' (default=" DEFAULT_NETWORK_DOWN_SCRIPT ")\n"
> +    "                to deconfigure it\n"
>       "                use '[down]script=no' to disable script execution\n"
> +    "                use network helper 'helper' (default=" DEFAULT_BRIDGE_HELPER ") and\n"
> +    "                bridge 'br' (default=" DEFAULT_BRIDGE_INTERFACE ") to configure it\n"
>       "                use 'fd=h' to connect to an already opened TAP interface\n"
>       "                use 'sndbuf=nbytes' to limit the size of the send buffer (the\n"
>       "                default is disabled 'sndbuf=0' to enable flow control set 'sndbuf=1048576')\n"
> @@ -1219,6 +1222,10 @@ DEF("net", HAS_ARG, QEMU_OPTION_net,
>       "                    (only has effect for virtio guests which use MSIX)\n"
>       "                use vhostforce=on to force vhost on for non-MSIX virtio guests\n"
>       "                use 'vhostfd=h' to connect to an already opened vhost net device\n"
> +    "-net bridge[,vlan=n][,name=str][,br=bridge][,helper=helper]\n"
> +    "                connects a host TAP network interface to a host bridge device 'br'\n"
> +    "                (default=" DEFAULT_BRIDGE_INTERFACE ") using the program 'helper'\n"
> +    "                (default=" DEFAULT_BRIDGE_HELPER ")\n"
>   #endif
>       "-net socket[,vlan=n][,name=str][,fd=h][,listen=[host]:port][,connect=host:port]\n"
>       "                connect the vlan 'n' to another VLAN using a socket connection\n"
> @@ -1242,6 +1249,7 @@ DEF("netdev", HAS_ARG, QEMU_OPTION_netdev,
>       "user|"
>   #endif
>       "tap|"
> +    "bridge|"
>   #ifdef CONFIG_VDE
>       "vde|"
>   #endif
> @@ -1378,26 +1386,66 @@ processed and applied to -net user. Mixing them with the new configuration
>   syntax gives undefined results. Their use for new applications is discouraged
>   as they will be removed from future versions.
>
> -@item -net tap[,vlan=@var{n}][,name=@var{name}][,fd=@var{h}][,ifname=@var{name}] [,script=@var{file}][,downscript=@var{dfile}]
> -Connect the host TAP network interface @var{name} to VLAN @var{n}, use
> -the network script @var{file} to configure it and the network script
> +@item -net tap[,vlan=@var{n}][,name=@var{name}][,fd=@var{h}][,ifname=@var{name}][,script=@var{file}][,downscript=@var{dfile}][,br=@var{bridge}][,helper=@var{helper}]
> +Connect the host TAP network interface @var{name} to VLAN @var{n}.
> +
> +Use the network script @var{file} to configure it and the network script
>   @var{dfile} to deconfigure it. If @var{name} is not provided, the OS
> -automatically provides one. @option{fd}=@var{h} can be used to specify
> -the handle of an already opened host TAP interface. The default network
> -configure script is @file{/etc/qemu-ifup} and the default network
> -deconfigure script is @file{/etc/qemu-ifdown}. Use @option{script=no}
> -or @option{downscript=no} to disable script execution. Example:
> +automatically provides one. The default network configure script is
> +@file{/etc/qemu-ifup} and the default network deconfigure script is
> +@file{/etc/qemu-ifdown}. Use @option{script=no} or @option{downscript=no}
> +to disable script execution.
> +
> +If running QEMU as an unprivileged user, use the network helper
> +@var{helper} to configure the TAP interface. The default network
> +helper executable is @file{/usr/local/libexec/qemu-bridge-helper}
> +and the default bridge device is @file{br0}.
> +
> +@option{fd}=@var{h} can be used to specify the handle of an already
> +opened host TAP interface.
> +
> +Examples:
>
>   @example
> +#launch a QEMU instance with the default network script
>   qemu linux.img -net nic -net tap
>   @end example
>
> -More complicated example (two NICs, each one connected to a TAP device)
>   @example
> +#launch a QEMU instance with two NICs, each one connected
> +#to a TAP device
>   qemu linux.img -net nic,vlan=0 -net tap,vlan=0,ifname=tap0 \
>                  -net nic,vlan=1 -net tap,vlan=1,ifname=tap1
>   @end example
>
> +@example
> +#launch a QEMU instance with the default network helper to
> +#connect a TAP device to bridge br0
> +qemu linux.img -net nic -net tap,helper=/usr/local/libexec/qemu-bridge-helper
> +@end example
> +
> +@item -net bridge[,vlan=@var{n}][,name=@var{name}][,br=@var{bridge}][,helper=@var{helper}]
> +Connect a host TAP network interface to a host bridge device.
> +
> +Use the network helper @var{helper} to configure the TAP interface and
> +attach it to the bridge. The default network helper executable is
> +@file{/usr/local/libexec/qemu-bridge-helper} and the default bridge
> +device is @file{br0}.
> +
> +Examples:
> +
> +@example
> +#launch a QEMU instance with the default network helper to
> +#connect a TAP device to bridge br0
> +qemu linux.img -net bridge -net nic,model=virtio
> +@end example
> +
> +@example
> +#launch a QEMU instance with the default network helper to
> +#connect a TAP device to bridge qemubr0
> +qemu linux.img -net bridge,br=qemubr0 -net nic,model=virtio
> +@end example
> +
>   @item -net socket[,vlan=@var{n}][,name=@var{name}][,fd=@var{h}] [,listen=[@var{host}]:@var{port}][,connect=@var{host}:@var{port}]
>
>   Connect the VLAN @var{n} to a remote VLAN in another QEMU virtual
Corey Bryant - Dec. 19, 2011, 10:55 p.m.
On 12/19/2011 02:36 PM, Anthony Liguori wrote:
> On 12/19/2011 07:11 AM, Corey Bryant wrote:
>> The most common use of -net tap is to connect a tap device to a
>> bridge. This
>> requires the use of a script and running qemu as root in order to
>> allocate a
>> tap device to pass to the script.
>>
>> This model is great for portability and flexibility but it's incredibly
>> difficult to eliminate the need to run qemu as root. The only really
>> viable
>> mechanism is to use tunctl to create a tap device, attach it to a
>> bridge as
>> root, and then hand that tap device to qemu. The problem with this
>> mechanism
>> is that it requires administrator intervention whenever a user wants
>> to create
>> a guest.
>>
>> By essentially writing a helper that implements the most common qemu-ifup
>> script that can be safely given cap_net_admin, we can dramatically
>> simplify
>> things for non-privileged users. We still support existing -net tap
>> options
>> as a mechanism for advanced users and backwards compatibility.
>>
>> Currently, this is very Linux centric but there's really no reason why it
>> couldn't be extended for other Unixes.
>>
>> A typical invocation would be similar to one of the following:
>>
>> qemu linux.img -net bridge -net nic,model=virtio
>>
>> qemu linux.img -net tap,helper=/usr/local/libexec/qemu-bridge-helper
>> -net nic,model=virtio
>>
>> qemu linux.img -netdev bridge,id=hn0
>> -device virtio-net-pci,netdev=hn0,id=nic1
>>
>> qemu linux.img -netdev
>> tap,helper=/usr/local/libexec/qemu-bridge-helper,id=hn0
>> -device virtio-net-pci,netdev=hn0,id=nic1
>>
>> The default bridge that we attach to is br0. The thinking is that a
>> distro
>> could preconfigure such an interface to allow out-of-the-box bridged
>> networking.
>>
>> Alternatively, if a user wants to use a different bridge, a typical
>> invocation
>> would be simliar to one of the following:
>>
>> qemu linux.img -net bridge,br=qemubr0 -net nic,model=virtio
>>
>> qemu linux.img -net
>> tap,helper=/usr/local/libexec/qemu-bridge-helper,br=qemubr0
>> -net nic,model=virtio
>>
>> qemu linux.img -netdev bridge,br=qemubr0,id=hn0
>> -device virtio-net-pci,netdev=hn0,id=nic1
>>
>> qemu linux.img -netdev
>> tap,helper=/usr/local/libexec/qemu-bridge-helper,br=qemubr0,id=hn0
>> -device virtio-net-pci,netdev=hn0,id=nic1
>>
>> Signed-off-by: Anthony Liguori<aliguori@us.ibm.com>
>> Signed-off-by: Richa Marwaha<rmarwah@linux.vnet.ibm.com>
>> Signed-off-by: Corey Bryant<coreyb@linux.vnet.ibm.com>
>> ---
>> configure | 2 +
>> net.c | 29 ++++++++-
>> net.h | 3 +
>> net/tap.c | 187 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>> net/tap.h | 3 +
>> qemu-options.hx | 74 ++++++++++++++++++----
>> 6 files changed, 281 insertions(+), 17 deletions(-)
>>
>> diff --git a/configure b/configure
>> index 6ed4196..4839694 100755
>> --- a/configure
>> +++ b/configure
>> @@ -2905,6 +2905,8 @@ echo "sysconfdir=$sysconfdir">> $config_host_mak
>> echo "docdir=$docdir">> $config_host_mak
>> echo "confdir=$confdir">> $config_host_mak
>> echo "libexecdir=\${prefix}/libexec">> $config_host_mak
>> +echo "CONFIG_QEMU_SHAREDIR=\"$prefix$datasuffix\"">> $config_host_mak
>> +echo "CONFIG_QEMU_HELPERDIR=\"$prefix/libexec\"">> $config_host_mak
>>
>> case "$cpu" in
>> i386|x86_64|alpha|arm|cris|hppa|ia64|lm32|m68k|microblaze|mips|mips64|ppc|ppc64|s390|s390x|sparc|sparc64|unicore32)
>>
>> diff --git a/net.c b/net.c
>> index f7bebf8..9296224 100644
>> --- a/net.c
>> +++ b/net.c
>> @@ -952,6 +952,14 @@ static const struct {
>> .type = QEMU_OPT_STRING,
>> .help = "script to shut down the interface",
>> }, {
>> + .name = "br",
>> + .type = QEMU_OPT_STRING,
>> + .help = "bridge name",
>> + }, {
>
> I don't think passing br= makes a whole of sense for -net tap. I think
> it would make more sense to make sure that helper could take a shell
> string so you could do:
>
> -netdev tap,helper="/usr/libexec/qemu-bridge-helper --br=br0"
>
> Regards,
>
> Anthony Liguori
>

Ok but do you think the -net bridge options should remain as-is?  It 
seems like execution of the helper should be consistent.  Here are the 
current options for -net bridge:

-net bridge,helper=/usr/local/libexec/qemu-bridge-helper,br=br0
Anthony Liguori - Dec. 19, 2011, 11:15 p.m.
On 12/19/2011 04:55 PM, Corey Bryant wrote:
>
>
>>> diff --git a/net.c b/net.c
>>> index f7bebf8..9296224 100644
>>> --- a/net.c
>>> +++ b/net.c
>>> @@ -952,6 +952,14 @@ static const struct {
>>> .type = QEMU_OPT_STRING,
>>> .help = "script to shut down the interface",
>>> }, {
>>> + .name = "br",
>>> + .type = QEMU_OPT_STRING,
>>> + .help = "bridge name",
>>> + }, {
>>
>> I don't think passing br= makes a whole of sense for -net tap. I think
>> it would make more sense to make sure that helper could take a shell
>> string so you could do:
>>
>> -netdev tap,helper="/usr/libexec/qemu-bridge-helper --br=br0"
>>
>> Regards,
>>
>> Anthony Liguori
>>
>
> Ok but do you think the -net bridge options should remain as-is? It seems like
> execution of the helper should be consistent. Here are the current options for
> -net bridge:
>
> -net bridge,helper=/usr/local/libexec/qemu-bridge-helper,br=br0

Yes.  -net bridge is syntactic sugar for -net tap with specific knowledge of the 
qemu-bridge-helper.

If someone wrote a 'qemu-openvswitch-helper' then you could imagine a '-net 
openvswitch' option that passed a bunch of openvswitch specific arguments.

Regards,

Anthony Liguori

>
hkran - Dec. 20, 2011, 10:02 a.m.
On 12/19/2011 09:11 PM, Corey Bryant wrote:
> The most common use of -net tap is to connect a tap device to a bridge.  This
> requires the use of a script and running qemu as root in order to allocate a
> tap device to pass to the script.
>
> This model is great for portability and flexibility but it's incredibly
> difficult to eliminate the need to run qemu as root.  The only really viable
> mechanism is to use tunctl to create a tap device, attach it to a bridge as
> root, and then hand that tap device to qemu.  The problem with this mechanism
> is that it requires administrator intervention whenever a user wants to create
> a guest.
>
> By essentially writing a helper that implements the most common qemu-ifup
> script that can be safely given cap_net_admin, we can dramatically simplify
> things for non-privileged users.  We still support existing -net tap options
> as a mechanism for advanced users and backwards compatibility.
>
> Currently, this is very Linux centric but there's really no reason why it
> couldn't be extended for other Unixes.
>
> A typical invocation would be similar to one of the following:
>
>    qemu linux.img -net bridge -net nic,model=virtio
>
>    qemu linux.img -net tap,helper=/usr/local/libexec/qemu-bridge-helper
>                   -net nic,model=virtio
>
>    qemu linux.img -netdev bridge,id=hn0
>                   -device virtio-net-pci,netdev=hn0,id=nic1
>
>    qemu linux.img -netdev tap,helper=/usr/local/libexec/qemu-bridge-helper,id=hn0
>                   -device virtio-net-pci,netdev=hn0,id=nic1
>
> The default bridge that we attach to is br0.  The thinking is that a distro
> could preconfigure such an interface to allow out-of-the-box bridged networking.
>
> Alternatively, if a user wants to use a different bridge, a typical invocation
> would be simliar to one of the following:
>
>    qemu linux.img -net bridge,br=qemubr0 -net nic,model=virtio
>
>    qemu linux.img -net tap,helper=/usr/local/libexec/qemu-bridge-helper,br=qemubr0
>                   -net nic,model=virtio
>
>    qemu linux.img -netdev bridge,br=qemubr0,id=hn0
>                   -device virtio-net-pci,netdev=hn0,id=nic1
>
>    qemu linux.img -netdev tap,helper=/usr/local/libexec/qemu-bridge-helper,br=qemubr0,id=hn0
>                   -device virtio-net-pci,netdev=hn0,id=nic1
>
> Signed-off-by: Anthony Liguori<aliguori@us.ibm.com>
> Signed-off-by: Richa Marwaha<rmarwah@linux.vnet.ibm.com>
> Signed-off-by: Corey Bryant<coreyb@linux.vnet.ibm.com>
> ---
>   configure       |    2 +
>   net.c           |   29 ++++++++-
>   net.h           |    3 +
>   net/tap.c       |  187 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>   net/tap.h       |    3 +
>   qemu-options.hx |   74 ++++++++++++++++++----
>   6 files changed, 281 insertions(+), 17 deletions(-)
>
> diff --git a/configure b/configure
> index 6ed4196..4839694 100755
> --- a/configure
> +++ b/configure
> @@ -2905,6 +2905,8 @@ echo "sysconfdir=$sysconfdir">>  $config_host_mak
>   echo "docdir=$docdir">>  $config_host_mak
>   echo "confdir=$confdir">>  $config_host_mak
>   echo "libexecdir=\${prefix}/libexec">>  $config_host_mak
> +echo "CONFIG_QEMU_SHAREDIR=\"$prefix$datasuffix\"">>  $config_host_mak
> +echo "CONFIG_QEMU_HELPERDIR=\"$prefix/libexec\"">>  $config_host_mak
>
>   case "$cpu" in
>     i386|x86_64|alpha|arm|cris|hppa|ia64|lm32|m68k|microblaze|mips|mips64|ppc|ppc64|s390|s390x|sparc|sparc64|unicore32)
> diff --git a/net.c b/net.c
> index f7bebf8..9296224 100644
> --- a/net.c
> +++ b/net.c
> @@ -952,6 +952,14 @@ static const struct {
>                   .type = QEMU_OPT_STRING,
>                   .help = "script to shut down the interface",
>               }, {
> +                .name = "br",
> +                .type = QEMU_OPT_STRING,
> +                .help = "bridge name",
> +            }, {
> +                .name = "helper",
> +                .type = QEMU_OPT_STRING,
> +                .help = "command to execute to configure bridge",
> +            }, {
>                   .name = "sndbuf",
>                   .type = QEMU_OPT_SIZE,
>                   .help = "send buffer limit"
> @@ -1049,6 +1057,23 @@ static const struct {
>               { /* end of list */ }
>           },
>       },
> +    [NET_CLIENT_TYPE_BRIDGE] = {
> +        .type = "bridge",
> +        .init = net_init_bridge,
> +        .desc = {
> +            NET_COMMON_PARAMS_DESC,
> +            {
> +                .name = "br",
> +                .type = QEMU_OPT_STRING,
> +                .help = "bridge name",
> +            }, {
> +                .name = "helper",
> +                .type = QEMU_OPT_STRING,
> +                .help = "command to execute to configure bridge",
> +            },
> +            { /* end of list */ }
> +        },
> +    },
>   };
>
>   int net_client_init(Monitor *mon, QemuOpts *opts, int is_netdev)
> @@ -1071,7 +1096,8 @@ int net_client_init(Monitor *mon, QemuOpts *opts, int is_netdev)
>   #ifdef CONFIG_VDE
>               strcmp(type, "vde") != 0&&
>   #endif
> -            strcmp(type, "socket") != 0) {
> +            strcmp(type, "socket") != 0&&
> +            strcmp(type, "bridge") != 0) {
>               qerror_report(QERR_INVALID_PARAMETER_VALUE, "type",
>                             "a netdev backend type");
>               return -1;
> @@ -1141,6 +1167,7 @@ static int net_host_check_device(const char *device)
>   #ifdef CONFIG_VDE
>                                          ,"vde"
>   #endif
> +                                       , "bridge"
>       };
>       for (i = 0; i<  sizeof(valid_param_list) / sizeof(char *); i++) {
>           if (!strncmp(valid_param_list[i], device,
> diff --git a/net.h b/net.h
> index c6b4190..0fd7e23 100644
> --- a/net.h
> +++ b/net.h
> @@ -36,6 +36,7 @@ typedef enum {
>       NET_CLIENT_TYPE_SOCKET,
>       NET_CLIENT_TYPE_VDE,
>       NET_CLIENT_TYPE_DUMP,
> +    NET_CLIENT_TYPE_BRIDGE,
>
>       NET_CLIENT_TYPE_MAX
>   } net_client_type;
> @@ -173,6 +174,8 @@ int do_netdev_del(Monitor *mon, const QDict *qdict, QObject **ret_data);
>
>   #define DEFAULT_NETWORK_SCRIPT "/etc/qemu-ifup"
>   #define DEFAULT_NETWORK_DOWN_SCRIPT "/etc/qemu-ifdown"
> +#define DEFAULT_BRIDGE_HELPER CONFIG_QEMU_HELPERDIR "/qemu-bridge-helper"
> +#define DEFAULT_BRIDGE_INTERFACE "br0"
>
>   void qdev_set_nic_properties(DeviceState *dev, NICInfo *nd);
>
> diff --git a/net/tap.c b/net/tap.c
> index 6c27a94..b2b82a1 100644
> --- a/net/tap.c
> +++ b/net/tap.c
> @@ -382,6 +382,143 @@ static int launch_script(const char *setup_script, const char *ifname, int fd)
>       return -1;
>   }
>
> +static int recv_fd(int c)
> +{
> +    int fd;
> +    uint8_t msgbuf[CMSG_SPACE(sizeof(fd))];
> +    struct msghdr msg = {
> +        .msg_control = msgbuf,
> +        .msg_controllen = sizeof(msgbuf),
> +    };
> +    struct cmsghdr *cmsg;
> +    struct iovec iov;
> +    uint8_t req[1];
> +    ssize_t len;
> +
> +    cmsg = CMSG_FIRSTHDR(&msg);
> +    cmsg->cmsg_level = SOL_SOCKET;
> +    cmsg->cmsg_type = SCM_RIGHTS;
> +    cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
> +    msg.msg_controllen = cmsg->cmsg_len;
> +
> +    iov.iov_base = req;
> +    iov.iov_len = sizeof(req);
> +
> +    msg.msg_iov =&iov;
> +    msg.msg_iovlen = 1;
> +
> +    len = recvmsg(c,&msg, 0);
> +    if (len>  0) {
> +        memcpy(&fd, CMSG_DATA(cmsg), sizeof(fd));
> +        return fd;
> +    }
> +
> +    return len;
> +}
> +
> +static int net_bridge_run_helper(const char *helper, const char *bridge)
> +{
> +    sigset_t oldmask, mask;
> +    int pid, status;
> +    char *args[5];
> +    char **parg;
> +    int sv[2];
> +
> +    sigemptyset(&mask);
> +    sigaddset(&mask, SIGCHLD);
> +    sigprocmask(SIG_BLOCK,&mask,&oldmask);
> +
> +    if (socketpair(PF_UNIX, SOCK_STREAM, 0, sv) == -1) {
> +        return -1;
> +    }
> +
> +    /* try to launch bridge helper */
> +    pid = fork();
> +    if (pid == 0) {
> +        int open_max = sysconf(_SC_OPEN_MAX), i;
> +        char buf[32];
> +
> +        snprintf(buf, sizeof(buf), "%d", sv[1]);
> +
> +        for (i = 0; i<  open_max; i++) {
> +            if (i != STDIN_FILENO&&
> +                i != STDOUT_FILENO&&
> +                i != STDERR_FILENO&&
> +                i != sv[1]) {
> +                close(i);
> +            }
> +        }
> +        parg = args;
> +        *parg++ = (char *)helper;
> +        *parg++ = (char *)"--use-vnet";
> +        *parg++ = (char *)bridge;
> +        *parg++ = buf;
> +        *parg++ = NULL;
> +        execv(helper, args);
> +        _exit(1);
> +    } else if (pid>  0) {
> +        int fd;
> +
> +        close(sv[1]);
> +
> +        do {
> +            fd = recv_fd(sv[0]);
> +        } while (fd == -1&&  errno == EINTR);
> +
> +        close(sv[0]);
> +
> +        while (waitpid(pid,&status, 0) != pid) {
> +            /* loop */
> +        }
> +        sigprocmask(SIG_SETMASK,&oldmask, NULL);
> +        if (fd<  0) {
> +            fprintf(stderr, "failed to recv file descriptor\n");
> +            return -1;
> +        }
> +
> +        if (WIFEXITED(status)&&  WEXITSTATUS(status) == 0) {
> +            return fd;
> +        }
> +    }
> +    fprintf(stderr, "failed to launch bridge helper\n");
> +    return -1;
> +}
> +
> +int net_init_bridge(QemuOpts *opts, Monitor *mon, const char *name,
> +                    VLANState *vlan)
> +{
> +    TAPState *s;
> +    int fd, vnet_hdr;
> +
> +    if (!qemu_opt_get(opts, "br")) {
> +        qemu_opt_set(opts, "br", DEFAULT_BRIDGE_INTERFACE);
> +    }
> +    if (!qemu_opt_get(opts, "helper")) {
> +        qemu_opt_set(opts, "helper", DEFAULT_BRIDGE_HELPER);
> +    }
> +
> +    fd = net_bridge_run_helper(qemu_opt_get(opts, "helper"),
> +                               qemu_opt_get(opts, "br"));
> +    if (fd == -1) {
> +        return -1;
> +    }
> +
> +    fcntl(fd, F_SETFL, O_NONBLOCK);
> +
> +    vnet_hdr = tap_probe_vnet_hdr(fd);
> +
> +    s = net_tap_fd_init(vlan, "bridge", name, fd, vnet_hdr);
> +    if (!s) {
> +        close(fd);
> +        return -1;
> +    }
> +
> +    snprintf(s->nc.info_str, sizeof(s->nc.info_str),
> +             "br=%s", qemu_opt_get(opts, "br"));
> +
> +    return 0;
> +}
> +
>   static int net_tap_init(QemuOpts *opts, int *vnet_hdr)
>   {
>       int fd, vnet_hdr_required;
> @@ -422,13 +559,17 @@ int net_init_tap(QemuOpts *opts, Monitor *mon, const char *name, VLANState *vlan
>   {
>       TAPState *s;
>       int fd, vnet_hdr = 0;
> +    const char *model;
>
>       if (qemu_opt_get(opts, "fd")) {
>           if (qemu_opt_get(opts, "ifname") ||
>               qemu_opt_get(opts, "script") ||
>               qemu_opt_get(opts, "downscript") ||
> -            qemu_opt_get(opts, "vnet_hdr")) {
> -            error_report("ifname=, script=, downscript= and vnet_hdr= is invalid with fd=");
> +            qemu_opt_get(opts, "vnet_hdr") ||
> +            qemu_opt_get(opts, "br") ||
> +            qemu_opt_get(opts, "helper")) {
> +            error_report("ifname=, script=, downscript=, vnet_hdr=, "
> +                         "br= and helper= are invalid with fd=");
>               return -1;
>           }
>
> @@ -440,7 +581,41 @@ int net_init_tap(QemuOpts *opts, Monitor *mon, const char *name, VLANState *vlan
>           fcntl(fd, F_SETFL, O_NONBLOCK);
>
>           vnet_hdr = tap_probe_vnet_hdr(fd);
> +
> +        model = "tap";
> +
> +    } else if (qemu_opt_get(opts, "helper")) {
> +        if (qemu_opt_get(opts, "ifname") ||
> +            qemu_opt_get(opts, "script") ||
> +            qemu_opt_get(opts, "downscript") ||
> +            qemu_opt_get(opts, "vnet_hdr")) {
> +            error_report("ifname=, script=, downscript=, and vnet_hdr= "
> +                         "are invalid with helper=");
> +            return -1;
> +        }
> +
> +        if (!qemu_opt_get(opts, "br")) {
> +            qemu_opt_set(opts, "br", DEFAULT_BRIDGE_INTERFACE);
> +        }
> +
> +        fd = net_bridge_run_helper(qemu_opt_get(opts, "helper"),
> +                                   qemu_opt_get(opts, "br"));
> +        if (fd == -1) {
> +            return -1;
> +        }
> +
> +        fcntl(fd, F_SETFL, O_NONBLOCK);
> +
> +        vnet_hdr = tap_probe_vnet_hdr(fd);
> +
> +        model = "bridge";
> +
>       } else {
> +        if (qemu_opt_get(opts, "br")) {
> +            error_report("br= is invalid with script=");
> +            return -1;
> +        }
> +
>           if (!qemu_opt_get(opts, "script")) {
>               qemu_opt_set(opts, "script", DEFAULT_NETWORK_SCRIPT);
>           }
> @@ -453,9 +628,11 @@ int net_init_tap(QemuOpts *opts, Monitor *mon, const char *name, VLANState *vlan
>           if (fd == -1) {
>               return -1;
>           }
> +
> +        model = "tap";
>       }
>
> -    s = net_tap_fd_init(vlan, "tap", name, fd, vnet_hdr);
> +    s = net_tap_fd_init(vlan, model, name, fd, vnet_hdr);
>       if (!s) {
>           close(fd);
>           return -1;
> @@ -467,6 +644,10 @@ int net_init_tap(QemuOpts *opts, Monitor *mon, const char *name, VLANState *vlan
>
>       if (qemu_opt_get(opts, "fd")) {
>           snprintf(s->nc.info_str, sizeof(s->nc.info_str), "fd=%d", fd);
> +    } else if (qemu_opt_get(opts, "helper")) {
> +        snprintf(s->nc.info_str, sizeof(s->nc.info_str),
> +                "helper=%s,br=%s", qemu_opt_get(opts, "helper"),
> +                qemu_opt_get(opts, "br"));
>       } else {
>           const char *ifname, *script, *downscript;
>
> diff --git a/net/tap.h b/net/tap.h
> index e44bd2b..56c591f 100644
> --- a/net/tap.h
> +++ b/net/tap.h
> @@ -57,4 +57,7 @@ int tap_get_fd(VLANClientState *vc);
>   struct vhost_net;
>   struct vhost_net *tap_get_vhost_net(VLANClientState *vc);
>
> +int net_init_bridge(QemuOpts *opts, Monitor *mon, const char *name,
> +                    VLANState *vlan);
> +
>   #endif /* QEMU_NET_TAP_H */
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 087a3b9..4f2385d 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -1205,11 +1205,14 @@ DEF("net", HAS_ARG, QEMU_OPTION_net,
>       "-net tap[,vlan=n][,name=str],ifname=name\n"
>       "                connect the host TAP network interface to VLAN 'n'\n"
>   #else
> -    "-net tap[,vlan=n][,name=str][,fd=h][,ifname=name][,script=file][,downscript=dfile][,sndbuf=nbytes][,vnet_hdr=on|off][,vhost=on|off][,vhostfd=h][,vhostforce=on|off]\n"
> -    "                connect the host TAP network interface to VLAN 'n' and use the\n"
> -    "                network scripts 'file' (default=" DEFAULT_NETWORK_SCRIPT ")\n"
> -    "                and 'dfile' (default=" DEFAULT_NETWORK_DOWN_SCRIPT ")\n"
> +    "-net tap[,vlan=n][,name=str][,fd=h][,ifname=name][,script=file][,downscript=dfile][,br=bridge][,helper=helper][,sndbuf=nbytes][,vnet_hdr=on|off][,vhost=on|off][,vhostfd=h][,vhostforce=on|off]\n"
> +    "                connect the host TAP network interface to VLAN 'n' \n"
> +    "                use network scripts 'file' (default=" DEFAULT_NETWORK_SCRIPT ")\n"
> +    "                to configure it and 'dfile' (default=" DEFAULT_NETWORK_DOWN_SCRIPT ")\n"
> +    "                to deconfigure it\n"
>       "                use '[down]script=no' to disable script execution\n"
> +    "                use network helper 'helper' (default=" DEFAULT_BRIDGE_HELPER ") and\n"
> +    "                bridge 'br' (default=" DEFAULT_BRIDGE_INTERFACE ") to configure it\n"
>       "                use 'fd=h' to connect to an already opened TAP interface\n"
>       "                use 'sndbuf=nbytes' to limit the size of the send buffer (the\n"
>       "                default is disabled 'sndbuf=0' to enable flow control set 'sndbuf=1048576')\n"
> @@ -1219,6 +1222,10 @@ DEF("net", HAS_ARG, QEMU_OPTION_net,
>       "                    (only has effect for virtio guests which use MSIX)\n"
>       "                use vhostforce=on to force vhost on for non-MSIX virtio guests\n"
>       "                use 'vhostfd=h' to connect to an already opened vhost net device\n"
> +    "-net bridge[,vlan=n][,name=str][,br=bridge][,helper=helper]\n"
> +    "                connects a host TAP network interface to a host bridge device 'br'\n"
> +    "                (default=" DEFAULT_BRIDGE_INTERFACE ") using the program 'helper'\n"
> +    "                (default=" DEFAULT_BRIDGE_HELPER ")\n"
>   #endif
>       "-net socket[,vlan=n][,name=str][,fd=h][,listen=[host]:port][,connect=host:port]\n"
>       "                connect the vlan 'n' to another VLAN using a socket connection\n"
> @@ -1242,6 +1249,7 @@ DEF("netdev", HAS_ARG, QEMU_OPTION_netdev,
>       "user|"
>   #endif
>       "tap|"
> +    "bridge|"
>   #ifdef CONFIG_VDE
>       "vde|"
>   #endif
> @@ -1378,26 +1386,66 @@ processed and applied to -net user. Mixing them with the new configuration
>   syntax gives undefined results. Their use for new applications is discouraged
>   as they will be removed from future versions.
>
> -@item -net tap[,vlan=@var{n}][,name=@var{name}][,fd=@var{h}][,ifname=@var{name}] [,script=@var{file}][,downscript=@var{dfile}]
> -Connect the host TAP network interface @var{name} to VLAN @var{n}, use
> -the network script @var{file} to configure it and the network script
> +@item -net tap[,vlan=@var{n}][,name=@var{name}][,fd=@var{h}][,ifname=@var{name}][,script=@var{file}][,downscript=@var{dfile}][,br=@var{bridge}][,helper=@var{helper}]
> +Connect the host TAP network interface @var{name} to VLAN @var{n}.
> +
> +Use the network script @var{file} to configure it and the network script
>   @var{dfile} to deconfigure it. If @var{name} is not provided, the OS
> -automatically provides one. @option{fd}=@var{h} can be used to specify
> -the handle of an already opened host TAP interface. The default network
> -configure script is @file{/etc/qemu-ifup} and the default network
> -deconfigure script is @file{/etc/qemu-ifdown}. Use @option{script=no}
> -or @option{downscript=no} to disable script execution. Example:
> +automatically provides one. The default network configure script is
> +@file{/etc/qemu-ifup} and the default network deconfigure script is
> +@file{/etc/qemu-ifdown}. Use @option{script=no} or @option{downscript=no}
> +to disable script execution.
> +
> +If running QEMU as an unprivileged user, use the network helper
> +@var{helper} to configure the TAP interface. The default network
> +helper executable is @file{/usr/local/libexec/qemu-bridge-helper}
> +and the default bridge device is @file{br0}.
> +
> +@option{fd}=@var{h} can be used to specify the handle of an already
> +opened host TAP interface.
> +
> +Examples:
>
>   @example
> +#launch a QEMU instance with the default network script
>   qemu linux.img -net nic -net tap
>   @end example
>
> -More complicated example (two NICs, each one connected to a TAP device)
>   @example
> +#launch a QEMU instance with two NICs, each one connected
> +#to a TAP device
>   qemu linux.img -net nic,vlan=0 -net tap,vlan=0,ifname=tap0 \
>                  -net nic,vlan=1 -net tap,vlan=1,ifname=tap1
>   @end example
>
> +@example
> +#launch a QEMU instance with the default network helper to
> +#connect a TAP device to bridge br0
> +qemu linux.img -net nic -net tap,helper=/usr/local/libexec/qemu-bridge-helper
> +@end example
> +
> +@item -net bridge[,vlan=@var{n}][,name=@var{name}][,br=@var{bridge}][,helper=@var{helper}]
> +Connect a host TAP network interface to a host bridge device.
> +
> +Use the network helper @var{helper} to configure the TAP interface and
> +attach it to the bridge. The default network helper executable is
> +@file{/usr/local/libexec/qemu-bridge-helper} and the default bridge
> +device is @file{br0}.
> +
> +Examples:
> +
> +@example
> +#launch a QEMU instance with the default network helper to
> +#connect a TAP device to bridge br0
> +qemu linux.img -net bridge -net nic,model=virtio
> +@end example
> +
> +@example
> +#launch a QEMU instance with the default network helper to
> +#connect a TAP device to bridge qemubr0
> +qemu linux.img -net bridge,br=qemubr0 -net nic,model=virtio
> +@end example
> +
>   @item -net socket[,vlan=@var{n}][,name=@var{name}][,fd=@var{h}] [,listen=[@var{host}]:@var{port}][,connect=@var{host}:@var{port}]
>
>   Connect the VLAN @var{n} to a remote VLAN in another QEMU virtual
Hi, I applied the patches, but an error  prompts there should be a file 
named bridge.conf ,
how can i find it?

/home/huikai/qemu10/bin/qemu-system-x86_64 -enable-kvm -m 1024 -drive 
file=imgs/sles.img,if=virtio -net bridge  -net nic,model=virtiofailed to 
parse default acl file `/home/huikai/qemu10/etc/qemu/bridge.conf'
failed to launch bridge helper
qemu-system-x86_64: -net bridge: Device 'bridge' could not be initialize
hkran - Dec. 20, 2011, 10:58 a.m.
On 12/20/2011 06:02 PM, Hui Kai Ran wrote:
> On 12/19/2011 09:11 PM, Corey Bryant wrote:
>> The most common use of -net tap is to connect a tap device to a 
>> bridge.  This
>> requires the use of a script and running qemu as root in order to 
>> allocate a
>> tap device to pass to the script.
>>
>> This model is great for portability and flexibility but it's incredibly
>> difficult to eliminate the need to run qemu as root.  The only really 
>> viable
>> mechanism is to use tunctl to create a tap device, attach it to a 
>> bridge as
>> root, and then hand that tap device to qemu.  The problem with this 
>> mechanism
>> is that it requires administrator intervention whenever a user wants 
>> to create
>> a guest.
>>
>> By essentially writing a helper that implements the most common 
>> qemu-ifup
>> script that can be safely given cap_net_admin, we can dramatically 
>> simplify
>> things for non-privileged users.  We still support existing -net tap 
>> options
>> as a mechanism for advanced users and backwards compatibility.
>>
>> Currently, this is very Linux centric but there's really no reason 
>> why it
>> couldn't be extended for other Unixes.
>>
>> A typical invocation would be similar to one of the following:
>>
>>    qemu linux.img -net bridge -net nic,model=virtio
>>
>>    qemu linux.img -net tap,helper=/usr/local/libexec/qemu-bridge-helper
>>                   -net nic,model=virtio
>>
>>    qemu linux.img -netdev bridge,id=hn0
>>                   -device virtio-net-pci,netdev=hn0,id=nic1
>>
>>    qemu linux.img -netdev 
>> tap,helper=/usr/local/libexec/qemu-bridge-helper,id=hn0
>>                   -device virtio-net-pci,netdev=hn0,id=nic1
>>
>> The default bridge that we attach to is br0.  The thinking is that a 
>> distro
>> could preconfigure such an interface to allow out-of-the-box bridged 
>> networking.
>>
>> Alternatively, if a user wants to use a different bridge, a typical 
>> invocation
>> would be simliar to one of the following:
>>
>>    qemu linux.img -net bridge,br=qemubr0 -net nic,model=virtio
>>
>>    qemu linux.img -net 
>> tap,helper=/usr/local/libexec/qemu-bridge-helper,br=qemubr0
>>                   -net nic,model=virtio
>>
>>    qemu linux.img -netdev bridge,br=qemubr0,id=hn0
>>                   -device virtio-net-pci,netdev=hn0,id=nic1
>>
>>    qemu linux.img -netdev 
>> tap,helper=/usr/local/libexec/qemu-bridge-helper,br=qemubr0,id=hn0
>>                   -device virtio-net-pci,netdev=hn0,id=nic1
>>
>> Signed-off-by: Anthony Liguori<aliguori@us.ibm.com>
>> Signed-off-by: Richa Marwaha<rmarwah@linux.vnet.ibm.com>
>> Signed-off-by: Corey Bryant<coreyb@linux.vnet.ibm.com>
>> ---
>>   configure       |    2 +
>>   net.c           |   29 ++++++++-
>>   net.h           |    3 +
>>   net/tap.c       |  187 
>> ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>>   net/tap.h       |    3 +
>>   qemu-options.hx |   74 ++++++++++++++++++----
>>   6 files changed, 281 insertions(+), 17 deletions(-)
>>
>> diff --git a/configure b/configure
>> index 6ed4196..4839694 100755
>> --- a/configure
>> +++ b/configure
>> @@ -2905,6 +2905,8 @@ echo "sysconfdir=$sysconfdir">>  $config_host_mak
>>   echo "docdir=$docdir">>  $config_host_mak
>>   echo "confdir=$confdir">>  $config_host_mak
>>   echo "libexecdir=\${prefix}/libexec">>  $config_host_mak
>> +echo "CONFIG_QEMU_SHAREDIR=\"$prefix$datasuffix\"">>  $config_host_mak
>> +echo "CONFIG_QEMU_HELPERDIR=\"$prefix/libexec\"">>  $config_host_mak
>>
>>   case "$cpu" in
>>     
>> i386|x86_64|alpha|arm|cris|hppa|ia64|lm32|m68k|microblaze|mips|mips64|ppc|ppc64|s390|s390x|sparc|sparc64|unicore32)
>> diff --git a/net.c b/net.c
>> index f7bebf8..9296224 100644
>> --- a/net.c
>> +++ b/net.c
>> @@ -952,6 +952,14 @@ static const struct {
>>                   .type = QEMU_OPT_STRING,
>>                   .help = "script to shut down the interface",
>>               }, {
>> +                .name = "br",
>> +                .type = QEMU_OPT_STRING,
>> +                .help = "bridge name",
>> +            }, {
>> +                .name = "helper",
>> +                .type = QEMU_OPT_STRING,
>> +                .help = "command to execute to configure bridge",
>> +            }, {
>>                   .name = "sndbuf",
>>                   .type = QEMU_OPT_SIZE,
>>                   .help = "send buffer limit"
>> @@ -1049,6 +1057,23 @@ static const struct {
>>               { /* end of list */ }
>>           },
>>       },
>> +    [NET_CLIENT_TYPE_BRIDGE] = {
>> +        .type = "bridge",
>> +        .init = net_init_bridge,
>> +        .desc = {
>> +            NET_COMMON_PARAMS_DESC,
>> +            {
>> +                .name = "br",
>> +                .type = QEMU_OPT_STRING,
>> +                .help = "bridge name",
>> +            }, {
>> +                .name = "helper",
>> +                .type = QEMU_OPT_STRING,
>> +                .help = "command to execute to configure bridge",
>> +            },
>> +            { /* end of list */ }
>> +        },
>> +    },
>>   };
>>
>>   int net_client_init(Monitor *mon, QemuOpts *opts, int is_netdev)
>> @@ -1071,7 +1096,8 @@ int net_client_init(Monitor *mon, QemuOpts 
>> *opts, int is_netdev)
>>   #ifdef CONFIG_VDE
>>               strcmp(type, "vde") != 0&&
>>   #endif
>> -            strcmp(type, "socket") != 0) {
>> +            strcmp(type, "socket") != 0&&
>> +            strcmp(type, "bridge") != 0) {
>>               qerror_report(QERR_INVALID_PARAMETER_VALUE, "type",
>>                             "a netdev backend type");
>>               return -1;
>> @@ -1141,6 +1167,7 @@ static int net_host_check_device(const char 
>> *device)
>>   #ifdef CONFIG_VDE
>>                                          ,"vde"
>>   #endif
>> +                                       , "bridge"
>>       };
>>       for (i = 0; i<  sizeof(valid_param_list) / sizeof(char *); i++) {
>>           if (!strncmp(valid_param_list[i], device,
>> diff --git a/net.h b/net.h
>> index c6b4190..0fd7e23 100644
>> --- a/net.h
>> +++ b/net.h
>> @@ -36,6 +36,7 @@ typedef enum {
>>       NET_CLIENT_TYPE_SOCKET,
>>       NET_CLIENT_TYPE_VDE,
>>       NET_CLIENT_TYPE_DUMP,
>> +    NET_CLIENT_TYPE_BRIDGE,
>>
>>       NET_CLIENT_TYPE_MAX
>>   } net_client_type;
>> @@ -173,6 +174,8 @@ int do_netdev_del(Monitor *mon, const QDict 
>> *qdict, QObject **ret_data);
>>
>>   #define DEFAULT_NETWORK_SCRIPT "/etc/qemu-ifup"
>>   #define DEFAULT_NETWORK_DOWN_SCRIPT "/etc/qemu-ifdown"
>> +#define DEFAULT_BRIDGE_HELPER CONFIG_QEMU_HELPERDIR 
>> "/qemu-bridge-helper"
>> +#define DEFAULT_BRIDGE_INTERFACE "br0"
>>
>>   void qdev_set_nic_properties(DeviceState *dev, NICInfo *nd);
>>
>> diff --git a/net/tap.c b/net/tap.c
>> index 6c27a94..b2b82a1 100644
>> --- a/net/tap.c
>> +++ b/net/tap.c
>> @@ -382,6 +382,143 @@ static int launch_script(const char 
>> *setup_script, const char *ifname, int fd)
>>       return -1;
>>   }
>>
>> +static int recv_fd(int c)
>> +{
>> +    int fd;
>> +    uint8_t msgbuf[CMSG_SPACE(sizeof(fd))];
>> +    struct msghdr msg = {
>> +        .msg_control = msgbuf,
>> +        .msg_controllen = sizeof(msgbuf),
>> +    };
>> +    struct cmsghdr *cmsg;
>> +    struct iovec iov;
>> +    uint8_t req[1];
>> +    ssize_t len;
>> +
>> +    cmsg = CMSG_FIRSTHDR(&msg);
>> +    cmsg->cmsg_level = SOL_SOCKET;
>> +    cmsg->cmsg_type = SCM_RIGHTS;
>> +    cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
>> +    msg.msg_controllen = cmsg->cmsg_len;
>> +
>> +    iov.iov_base = req;
>> +    iov.iov_len = sizeof(req);
>> +
>> +    msg.msg_iov =&iov;
>> +    msg.msg_iovlen = 1;
>> +
>> +    len = recvmsg(c,&msg, 0);
>> +    if (len>  0) {
>> +        memcpy(&fd, CMSG_DATA(cmsg), sizeof(fd));
>> +        return fd;
>> +    }
>> +
>> +    return len;
>> +}
>> +
>> +static int net_bridge_run_helper(const char *helper, const char 
>> *bridge)
>> +{
>> +    sigset_t oldmask, mask;
>> +    int pid, status;
>> +    char *args[5];
>> +    char **parg;
>> +    int sv[2];
>> +
>> +    sigemptyset(&mask);
>> +    sigaddset(&mask, SIGCHLD);
>> +    sigprocmask(SIG_BLOCK,&mask,&oldmask);
>> +
>> +    if (socketpair(PF_UNIX, SOCK_STREAM, 0, sv) == -1) {
>> +        return -1;
>> +    }
>> +
>> +    /* try to launch bridge helper */
>> +    pid = fork();
>> +    if (pid == 0) {
>> +        int open_max = sysconf(_SC_OPEN_MAX), i;
>> +        char buf[32];
>> +
>> +        snprintf(buf, sizeof(buf), "%d", sv[1]);
>> +
>> +        for (i = 0; i<  open_max; i++) {
>> +            if (i != STDIN_FILENO&&
>> +                i != STDOUT_FILENO&&
>> +                i != STDERR_FILENO&&
>> +                i != sv[1]) {
>> +                close(i);
>> +            }
>> +        }
>> +        parg = args;
>> +        *parg++ = (char *)helper;
>> +        *parg++ = (char *)"--use-vnet";
>> +        *parg++ = (char *)bridge;
>> +        *parg++ = buf;
>> +        *parg++ = NULL;
>> +        execv(helper, args);
>> +        _exit(1);
>> +    } else if (pid>  0) {
>> +        int fd;
>> +
>> +        close(sv[1]);
>> +
>> +        do {
>> +            fd = recv_fd(sv[0]);
>> +        } while (fd == -1&&  errno == EINTR);
>> +
>> +        close(sv[0]);
>> +
>> +        while (waitpid(pid,&status, 0) != pid) {
>> +            /* loop */
>> +        }
>> +        sigprocmask(SIG_SETMASK,&oldmask, NULL);
>> +        if (fd<  0) {
>> +            fprintf(stderr, "failed to recv file descriptor\n");
>> +            return -1;
>> +        }
>> +
>> +        if (WIFEXITED(status)&&  WEXITSTATUS(status) == 0) {
>> +            return fd;
>> +        }
>> +    }
>> +    fprintf(stderr, "failed to launch bridge helper\n");
>> +    return -1;
>> +}
>> +
>> +int net_init_bridge(QemuOpts *opts, Monitor *mon, const char *name,
>> +                    VLANState *vlan)
>> +{
>> +    TAPState *s;
>> +    int fd, vnet_hdr;
>> +
>> +    if (!qemu_opt_get(opts, "br")) {
>> +        qemu_opt_set(opts, "br", DEFAULT_BRIDGE_INTERFACE);
>> +    }
>> +    if (!qemu_opt_get(opts, "helper")) {
>> +        qemu_opt_set(opts, "helper", DEFAULT_BRIDGE_HELPER);
>> +    }
>> +
>> +    fd = net_bridge_run_helper(qemu_opt_get(opts, "helper"),
>> +                               qemu_opt_get(opts, "br"));
>> +    if (fd == -1) {
>> +        return -1;
>> +    }
>> +
>> +    fcntl(fd, F_SETFL, O_NONBLOCK);
>> +
>> +    vnet_hdr = tap_probe_vnet_hdr(fd);
>> +
>> +    s = net_tap_fd_init(vlan, "bridge", name, fd, vnet_hdr);
>> +    if (!s) {
>> +        close(fd);
>> +        return -1;
>> +    }
>> +
>> +    snprintf(s->nc.info_str, sizeof(s->nc.info_str),
>> +             "br=%s", qemu_opt_get(opts, "br"));
>> +
>> +    return 0;
>> +}
>> +
>>   static int net_tap_init(QemuOpts *opts, int *vnet_hdr)
>>   {
>>       int fd, vnet_hdr_required;
>> @@ -422,13 +559,17 @@ int net_init_tap(QemuOpts *opts, Monitor *mon, 
>> const char *name, VLANState *vlan
>>   {
>>       TAPState *s;
>>       int fd, vnet_hdr = 0;
>> +    const char *model;
>>
>>       if (qemu_opt_get(opts, "fd")) {
>>           if (qemu_opt_get(opts, "ifname") ||
>>               qemu_opt_get(opts, "script") ||
>>               qemu_opt_get(opts, "downscript") ||
>> -            qemu_opt_get(opts, "vnet_hdr")) {
>> -            error_report("ifname=, script=, downscript= and 
>> vnet_hdr= is invalid with fd=");
>> +            qemu_opt_get(opts, "vnet_hdr") ||
>> +            qemu_opt_get(opts, "br") ||
>> +            qemu_opt_get(opts, "helper")) {
>> +            error_report("ifname=, script=, downscript=, vnet_hdr=, "
>> +                         "br= and helper= are invalid with fd=");
>>               return -1;
>>           }
>>
>> @@ -440,7 +581,41 @@ int net_init_tap(QemuOpts *opts, Monitor *mon, 
>> const char *name, VLANState *vlan
>>           fcntl(fd, F_SETFL, O_NONBLOCK);
>>
>>           vnet_hdr = tap_probe_vnet_hdr(fd);
>> +
>> +        model = "tap";
>> +
>> +    } else if (qemu_opt_get(opts, "helper")) {
>> +        if (qemu_opt_get(opts, "ifname") ||
>> +            qemu_opt_get(opts, "script") ||
>> +            qemu_opt_get(opts, "downscript") ||
>> +            qemu_opt_get(opts, "vnet_hdr")) {
>> +            error_report("ifname=, script=, downscript=, and 
>> vnet_hdr= "
>> +                         "are invalid with helper=");
>> +            return -1;
>> +        }
>> +
>> +        if (!qemu_opt_get(opts, "br")) {
>> +            qemu_opt_set(opts, "br", DEFAULT_BRIDGE_INTERFACE);
>> +        }
>> +
>> +        fd = net_bridge_run_helper(qemu_opt_get(opts, "helper"),
>> +                                   qemu_opt_get(opts, "br"));
>> +        if (fd == -1) {
>> +            return -1;
>> +        }
>> +
>> +        fcntl(fd, F_SETFL, O_NONBLOCK);
>> +
>> +        vnet_hdr = tap_probe_vnet_hdr(fd);
>> +
>> +        model = "bridge";
>> +
>>       } else {
>> +        if (qemu_opt_get(opts, "br")) {
>> +            error_report("br= is invalid with script=");
>> +            return -1;
>> +        }
>> +
>>           if (!qemu_opt_get(opts, "script")) {
>>               qemu_opt_set(opts, "script", DEFAULT_NETWORK_SCRIPT);
>>           }
>> @@ -453,9 +628,11 @@ int net_init_tap(QemuOpts *opts, Monitor *mon, 
>> const char *name, VLANState *vlan
>>           if (fd == -1) {
>>               return -1;
>>           }
>> +
>> +        model = "tap";
>>       }
>>
>> -    s = net_tap_fd_init(vlan, "tap", name, fd, vnet_hdr);
>> +    s = net_tap_fd_init(vlan, model, name, fd, vnet_hdr);
>>       if (!s) {
>>           close(fd);
>>           return -1;
>> @@ -467,6 +644,10 @@ int net_init_tap(QemuOpts *opts, Monitor *mon, 
>> const char *name, VLANState *vlan
>>
>>       if (qemu_opt_get(opts, "fd")) {
>>           snprintf(s->nc.info_str, sizeof(s->nc.info_str), "fd=%d", fd);
>> +    } else if (qemu_opt_get(opts, "helper")) {
>> +        snprintf(s->nc.info_str, sizeof(s->nc.info_str),
>> +                "helper=%s,br=%s", qemu_opt_get(opts, "helper"),
>> +                qemu_opt_get(opts, "br"));
>>       } else {
>>           const char *ifname, *script, *downscript;
>>
>> diff --git a/net/tap.h b/net/tap.h
>> index e44bd2b..56c591f 100644
>> --- a/net/tap.h
>> +++ b/net/tap.h
>> @@ -57,4 +57,7 @@ int tap_get_fd(VLANClientState *vc);
>>   struct vhost_net;
>>   struct vhost_net *tap_get_vhost_net(VLANClientState *vc);
>>
>> +int net_init_bridge(QemuOpts *opts, Monitor *mon, const char *name,
>> +                    VLANState *vlan);
>> +
>>   #endif /* QEMU_NET_TAP_H */
>> diff --git a/qemu-options.hx b/qemu-options.hx
>> index 087a3b9..4f2385d 100644
>> --- a/qemu-options.hx
>> +++ b/qemu-options.hx
>> @@ -1205,11 +1205,14 @@ DEF("net", HAS_ARG, QEMU_OPTION_net,
>>       "-net tap[,vlan=n][,name=str],ifname=name\n"
>>       "                connect the host TAP network interface to VLAN 
>> 'n'\n"
>>   #else
>> -    "-net 
>> tap[,vlan=n][,name=str][,fd=h][,ifname=name][,script=file][,downscript=dfile][,sndbuf=nbytes][,vnet_hdr=on|off][,vhost=on|off][,vhostfd=h][,vhostforce=on|off]\n"
>> -    "                connect the host TAP network interface to VLAN 
>> 'n' and use the\n"
>> -    "                network scripts 'file' (default=" 
>> DEFAULT_NETWORK_SCRIPT ")\n"
>> -    "                and 'dfile' (default=" 
>> DEFAULT_NETWORK_DOWN_SCRIPT ")\n"
>> +    "-net 
>> tap[,vlan=n][,name=str][,fd=h][,ifname=name][,script=file][,downscript=dfile][,br=bridge][,helper=helper][,sndbuf=nbytes][,vnet_hdr=on|off][,vhost=on|off][,vhostfd=h][,vhostforce=on|off]\n"
>> +    "                connect the host TAP network interface to VLAN 
>> 'n' \n"
>> +    "                use network scripts 'file' (default=" 
>> DEFAULT_NETWORK_SCRIPT ")\n"
>> +    "                to configure it and 'dfile' (default=" 
>> DEFAULT_NETWORK_DOWN_SCRIPT ")\n"
>> +    "                to deconfigure it\n"
>>       "                use '[down]script=no' to disable script 
>> execution\n"
>> +    "                use network helper 'helper' (default=" 
>> DEFAULT_BRIDGE_HELPER ") and\n"
>> +    "                bridge 'br' (default=" DEFAULT_BRIDGE_INTERFACE 
>> ") to configure it\n"
>>       "                use 'fd=h' to connect to an already opened TAP 
>> interface\n"
>>       "                use 'sndbuf=nbytes' to limit the size of the 
>> send buffer (the\n"
>>       "                default is disabled 'sndbuf=0' to enable flow 
>> control set 'sndbuf=1048576')\n"
>> @@ -1219,6 +1222,10 @@ DEF("net", HAS_ARG, QEMU_OPTION_net,
>>       "                    (only has effect for virtio guests which 
>> use MSIX)\n"
>>       "                use vhostforce=on to force vhost on for 
>> non-MSIX virtio guests\n"
>>       "                use 'vhostfd=h' to connect to an already 
>> opened vhost net device\n"
>> +    "-net bridge[,vlan=n][,name=str][,br=bridge][,helper=helper]\n"
>> +    "                connects a host TAP network interface to a host 
>> bridge device 'br'\n"
>> +    "                (default=" DEFAULT_BRIDGE_INTERFACE ") using 
>> the program 'helper'\n"
>> +    "                (default=" DEFAULT_BRIDGE_HELPER ")\n"
>>   #endif
>>       "-net 
>> socket[,vlan=n][,name=str][,fd=h][,listen=[host]:port][,connect=host:port]\n"
>>       "                connect the vlan 'n' to another VLAN using a 
>> socket connection\n"
>> @@ -1242,6 +1249,7 @@ DEF("netdev", HAS_ARG, QEMU_OPTION_netdev,
>>       "user|"
>>   #endif
>>       "tap|"
>> +    "bridge|"
>>   #ifdef CONFIG_VDE
>>       "vde|"
>>   #endif
>> @@ -1378,26 +1386,66 @@ processed and applied to -net user. Mixing 
>> them with the new configuration
>>   syntax gives undefined results. Their use for new applications is 
>> discouraged
>>   as they will be removed from future versions.
>>
>> -@item -net 
>> tap[,vlan=@var{n}][,name=@var{name}][,fd=@var{h}][,ifname=@var{name}] 
>> [,script=@var{file}][,downscript=@var{dfile}]
>> -Connect the host TAP network interface @var{name} to VLAN @var{n}, use
>> -the network script @var{file} to configure it and the network script
>> +@item -net 
>> tap[,vlan=@var{n}][,name=@var{name}][,fd=@var{h}][,ifname=@var{name}][,script=@var{file}][,downscript=@var{dfile}][,br=@var{bridge}][,helper=@var{helper}]
>> +Connect the host TAP network interface @var{name} to VLAN @var{n}.
>> +
>> +Use the network script @var{file} to configure it and the network 
>> script
>>   @var{dfile} to deconfigure it. If @var{name} is not provided, the OS
>> -automatically provides one. @option{fd}=@var{h} can be used to specify
>> -the handle of an already opened host TAP interface. The default network
>> -configure script is @file{/etc/qemu-ifup} and the default network
>> -deconfigure script is @file{/etc/qemu-ifdown}. Use @option{script=no}
>> -or @option{downscript=no} to disable script execution. Example:
>> +automatically provides one. The default network configure script is
>> +@file{/etc/qemu-ifup} and the default network deconfigure script is
>> +@file{/etc/qemu-ifdown}. Use @option{script=no} or 
>> @option{downscript=no}
>> +to disable script execution.
>> +
>> +If running QEMU as an unprivileged user, use the network helper
>> +@var{helper} to configure the TAP interface. The default network
>> +helper executable is @file{/usr/local/libexec/qemu-bridge-helper}
>> +and the default bridge device is @file{br0}.
>> +
>> +@option{fd}=@var{h} can be used to specify the handle of an already
>> +opened host TAP interface.
>> +
>> +Examples:
>>
>>   @example
>> +#launch a QEMU instance with the default network script
>>   qemu linux.img -net nic -net tap
>>   @end example
>>
>> -More complicated example (two NICs, each one connected to a TAP device)
>>   @example
>> +#launch a QEMU instance with two NICs, each one connected
>> +#to a TAP device
>>   qemu linux.img -net nic,vlan=0 -net tap,vlan=0,ifname=tap0 \
>>                  -net nic,vlan=1 -net tap,vlan=1,ifname=tap1
>>   @end example
>>
>> +@example
>> +#launch a QEMU instance with the default network helper to
>> +#connect a TAP device to bridge br0
>> +qemu linux.img -net nic -net 
>> tap,helper=/usr/local/libexec/qemu-bridge-helper
>> +@end example
>> +
>> +@item -net 
>> bridge[,vlan=@var{n}][,name=@var{name}][,br=@var{bridge}][,helper=@var{helper}]
>> +Connect a host TAP network interface to a host bridge device.
>> +
>> +Use the network helper @var{helper} to configure the TAP interface and
>> +attach it to the bridge. The default network helper executable is
>> +@file{/usr/local/libexec/qemu-bridge-helper} and the default bridge
>> +device is @file{br0}.
>> +
>> +Examples:
>> +
>> +@example
>> +#launch a QEMU instance with the default network helper to
>> +#connect a TAP device to bridge br0
>> +qemu linux.img -net bridge -net nic,model=virtio
>> +@end example
>> +
>> +@example
>> +#launch a QEMU instance with the default network helper to
>> +#connect a TAP device to bridge qemubr0
>> +qemu linux.img -net bridge,br=qemubr0 -net nic,model=virtio
>> +@end example
>> +
>>   @item -net socket[,vlan=@var{n}][,name=@var{name}][,fd=@var{h}] 
>> [,listen=[@var{host}]:@var{port}][,connect=@var{host}:@var{port}]
>>
>>   Connect the VLAN @var{n} to a remote VLAN in another QEMU virtual
> Hi, I applied the patches, but an error  prompts there should be a 
> file named bridge.conf ,
> how can i find it?
>
> /home/huikai/qemu10/bin/qemu-system-x86_64 -enable-kvm -m 1024 -drive 
> file=imgs/sles.img,if=virtio -net bridge  -net nic,model=virtiofailed 
> to parse default acl file `/home/huikai/qemu10/etc/qemu/bridge.conf'
> failed to launch bridge helper
> qemu-system-x86_64: -net bridge: Device 'bridge' could not be initialize
>
>
Sorry, i found it in the patch set.
Corey Bryant - Dec. 20, 2011, 5:13 p.m.
On 12/19/2011 06:15 PM, Anthony Liguori wrote:
> On 12/19/2011 04:55 PM, Corey Bryant wrote:
>>
>>
>>>> diff --git a/net.c b/net.c
>>>> index f7bebf8..9296224 100644
>>>> --- a/net.c
>>>> +++ b/net.c
>>>> @@ -952,6 +952,14 @@ static const struct {
>>>> .type = QEMU_OPT_STRING,
>>>> .help = "script to shut down the interface",
>>>> }, {
>>>> + .name = "br",
>>>> + .type = QEMU_OPT_STRING,
>>>> + .help = "bridge name",
>>>> + }, {
>>>
>>> I don't think passing br= makes a whole of sense for -net tap. I think
>>> it would make more sense to make sure that helper could take a shell
>>> string so you could do:
>>>
>>> -netdev tap,helper="/usr/libexec/qemu-bridge-helper --br=br0"
>>>
>>> Regards,
>>>
>>> Anthony Liguori
>>>
>>
>> Ok but do you think the -net bridge options should remain as-is? It
>> seems like
>> execution of the helper should be consistent. Here are the current
>> options for
>> -net bridge:
>>
>> -net bridge,helper=/usr/local/libexec/qemu-bridge-helper,br=br0
>
> Yes. -net bridge is syntactic sugar for -net tap with specific knowledge
> of the qemu-bridge-helper.
>
> If someone wrote a 'qemu-openvswitch-helper' then you could imagine a
> '-net openvswitch' option that passed a bunch of openvswitch specific
> arguments.
>
> Regards,
>
> Anthony Liguori
>
>>
>
>

It seems like the helper should accept the following arguments:

--vnet-hdr --br=<bridge name> --fd=<unix fd>

(It already accept these, but the --br= and --fd= syntax aren't required 
at the moment.)

Then QEMU would only allow the following to be specified for -netdev tap:

-netdev tap,helper="/usr/libexec/qemu-bridge-helper"
or
-netdev tap,helper="/usr/libexec/qemu-bridge-helper --br=bridge"

and would ignore or reject --vnet-hdr and --fd=.  --vnet-hdr and --fd= 
would always be specified internally when the helper is exec'd.
Anthony Liguori - Dec. 22, 2011, 3:54 p.m.
On 12/20/2011 11:13 AM, Corey Bryant wrote:
>
>
> On 12/19/2011 06:15 PM, Anthony Liguori wrote:
>> On 12/19/2011 04:55 PM, Corey Bryant wrote:
>>>
>>>
>>>>> diff --git a/net.c b/net.c
>>>>> index f7bebf8..9296224 100644
>>>>> --- a/net.c
>>>>> +++ b/net.c
>>>>> @@ -952,6 +952,14 @@ static const struct {
>>>>> .type = QEMU_OPT_STRING,
>>>>> .help = "script to shut down the interface",
>>>>> }, {
>>>>> + .name = "br",
>>>>> + .type = QEMU_OPT_STRING,
>>>>> + .help = "bridge name",
>>>>> + }, {
>>>>
>>>> I don't think passing br= makes a whole of sense for -net tap. I think
>>>> it would make more sense to make sure that helper could take a shell
>>>> string so you could do:
>>>>
>>>> -netdev tap,helper="/usr/libexec/qemu-bridge-helper --br=br0"
>>>>
>>>> Regards,
>>>>
>>>> Anthony Liguori
>>>>
>>>
>>> Ok but do you think the -net bridge options should remain as-is? It
>>> seems like
>>> execution of the helper should be consistent. Here are the current
>>> options for
>>> -net bridge:
>>>
>>> -net bridge,helper=/usr/local/libexec/qemu-bridge-helper,br=br0
>>
>> Yes. -net bridge is syntactic sugar for -net tap with specific knowledge
>> of the qemu-bridge-helper.
>>
>> If someone wrote a 'qemu-openvswitch-helper' then you could imagine a
>> '-net openvswitch' option that passed a bunch of openvswitch specific
>> arguments.
>>
>> Regards,
>>
>> Anthony Liguori
>>
>>>
>>
>>
>
> It seems like the helper should accept the following arguments:
>
> --vnet-hdr --br=<bridge name> --fd=<unix fd>
>
> (It already accept these, but the --br= and --fd= syntax aren't required at the
> moment.)
>
> Then QEMU would only allow the following to be specified for -netdev tap:
>
> -netdev tap,helper="/usr/libexec/qemu-bridge-helper"
> or
> -netdev tap,helper="/usr/libexec/qemu-bridge-helper --br=bridge"
>
> and would ignore or reject --vnet-hdr and --fd=. --vnet-hdr and --fd= would
> always be specified internally when the helper is exec'd.

I don't know what you mean by "ignore or reject".  Just take whatever the helper 
string is, concat " --vnet-hdr --fd=" as appropriate, and execute it via /bin/sh.

Regards,

Anthony Liguori

>

Patch

difficult to eliminate the need to run qemu as root.  The only really viable
mechanism is to use tunctl to create a tap device, attach it to a bridge as
root, and then hand that tap device to qemu.  The problem with this mechanism
is that it requires administrator intervention whenever a user wants to create
a guest.

By essentially writing a helper that implements the most common qemu-ifup
script that can be safely given cap_net_admin, we can dramatically simplify
things for non-privileged users.  We still support existing -net tap options
as a mechanism for advanced users and backwards compatibility.

Currently, this is very Linux centric but there's really no reason why it
couldn't be extended for other Unixes.

A typical invocation would be similar to one of the following:

  qemu linux.img -net bridge -net nic,model=virtio

  qemu linux.img -net tap,helper=/usr/local/libexec/qemu-bridge-helper
                 -net nic,model=virtio

  qemu linux.img -netdev bridge,id=hn0
                 -device virtio-net-pci,netdev=hn0,id=nic1

  qemu linux.img -netdev tap,helper=/usr/local/libexec/qemu-bridge-helper,id=hn0
                 -device virtio-net-pci,netdev=hn0,id=nic1

The default bridge that we attach to is br0.  The thinking is that a distro
could preconfigure such an interface to allow out-of-the-box bridged networking.

Alternatively, if a user wants to use a different bridge, a typical invocation
would be simliar to one of the following:

  qemu linux.img -net bridge,br=qemubr0 -net nic,model=virtio

  qemu linux.img -net tap,helper=/usr/local/libexec/qemu-bridge-helper,br=qemubr0
                 -net nic,model=virtio

  qemu linux.img -netdev bridge,br=qemubr0,id=hn0
                 -device virtio-net-pci,netdev=hn0,id=nic1

  qemu linux.img -netdev tap,helper=/usr/local/libexec/qemu-bridge-helper,br=qemubr0,id=hn0
                 -device virtio-net-pci,netdev=hn0,id=nic1

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
Signed-off-by: Richa Marwaha <rmarwah@linux.vnet.ibm.com>
Signed-off-by: Corey Bryant <coreyb@linux.vnet.ibm.com>
---
 configure       |    2 +
 net.c           |   29 ++++++++-
 net.h           |    3 +
 net/tap.c       |  187 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 net/tap.h       |    3 +
 qemu-options.hx |   74 ++++++++++++++++++----
 6 files changed, 281 insertions(+), 17 deletions(-)

diff --git a/configure b/configure
index 6ed4196..4839694 100755
--- a/configure
+++ b/configure
@@ -2905,6 +2905,8 @@  echo "sysconfdir=$sysconfdir" >> $config_host_mak
 echo "docdir=$docdir" >> $config_host_mak
 echo "confdir=$confdir" >> $config_host_mak
 echo "libexecdir=\${prefix}/libexec" >> $config_host_mak
+echo "CONFIG_QEMU_SHAREDIR=\"$prefix$datasuffix\"" >> $config_host_mak
+echo "CONFIG_QEMU_HELPERDIR=\"$prefix/libexec\"" >> $config_host_mak
 
 case "$cpu" in
   i386|x86_64|alpha|arm|cris|hppa|ia64|lm32|m68k|microblaze|mips|mips64|ppc|ppc64|s390|s390x|sparc|sparc64|unicore32)
diff --git a/net.c b/net.c
index f7bebf8..9296224 100644
--- a/net.c
+++ b/net.c
@@ -952,6 +952,14 @@  static const struct {
                 .type = QEMU_OPT_STRING,
                 .help = "script to shut down the interface",
             }, {
+                .name = "br",
+                .type = QEMU_OPT_STRING,
+                .help = "bridge name",
+            }, {
+                .name = "helper",
+                .type = QEMU_OPT_STRING,
+                .help = "command to execute to configure bridge",
+            }, {
                 .name = "sndbuf",
                 .type = QEMU_OPT_SIZE,
                 .help = "send buffer limit"
@@ -1049,6 +1057,23 @@  static const struct {
             { /* end of list */ }
         },
     },
+    [NET_CLIENT_TYPE_BRIDGE] = {
+        .type = "bridge",
+        .init = net_init_bridge,
+        .desc = {
+            NET_COMMON_PARAMS_DESC,
+            {
+                .name = "br",
+                .type = QEMU_OPT_STRING,
+                .help = "bridge name",
+            }, {
+                .name = "helper",
+                .type = QEMU_OPT_STRING,
+                .help = "command to execute to configure bridge",
+            },
+            { /* end of list */ }
+        },
+    },
 };
 
 int net_client_init(Monitor *mon, QemuOpts *opts, int is_netdev)
@@ -1071,7 +1096,8 @@  int net_client_init(Monitor *mon, QemuOpts *opts, int is_netdev)
 #ifdef CONFIG_VDE
             strcmp(type, "vde") != 0 &&
 #endif
-            strcmp(type, "socket") != 0) {
+            strcmp(type, "socket") != 0 &&
+            strcmp(type, "bridge") != 0) {
             qerror_report(QERR_INVALID_PARAMETER_VALUE, "type",
                           "a netdev backend type");
             return -1;
@@ -1141,6 +1167,7 @@  static int net_host_check_device(const char *device)
 #ifdef CONFIG_VDE
                                        ,"vde"
 #endif
+                                       , "bridge"
     };
     for (i = 0; i < sizeof(valid_param_list) / sizeof(char *); i++) {
         if (!strncmp(valid_param_list[i], device,
diff --git a/net.h b/net.h
index c6b4190..0fd7e23 100644
--- a/net.h
+++ b/net.h
@@ -36,6 +36,7 @@  typedef enum {
     NET_CLIENT_TYPE_SOCKET,
     NET_CLIENT_TYPE_VDE,
     NET_CLIENT_TYPE_DUMP,
+    NET_CLIENT_TYPE_BRIDGE,
 
     NET_CLIENT_TYPE_MAX
 } net_client_type;
@@ -173,6 +174,8 @@  int do_netdev_del(Monitor *mon, const QDict *qdict, QObject **ret_data);
 
 #define DEFAULT_NETWORK_SCRIPT "/etc/qemu-ifup"
 #define DEFAULT_NETWORK_DOWN_SCRIPT "/etc/qemu-ifdown"
+#define DEFAULT_BRIDGE_HELPER CONFIG_QEMU_HELPERDIR "/qemu-bridge-helper"
+#define DEFAULT_BRIDGE_INTERFACE "br0"
 
 void qdev_set_nic_properties(DeviceState *dev, NICInfo *nd);
 
diff --git a/net/tap.c b/net/tap.c
index 6c27a94..b2b82a1 100644
--- a/net/tap.c
+++ b/net/tap.c
@@ -382,6 +382,143 @@  static int launch_script(const char *setup_script, const char *ifname, int fd)
     return -1;
 }
 
+static int recv_fd(int c)
+{
+    int fd;
+    uint8_t msgbuf[CMSG_SPACE(sizeof(fd))];
+    struct msghdr msg = {
+        .msg_control = msgbuf,
+        .msg_controllen = sizeof(msgbuf),
+    };
+    struct cmsghdr *cmsg;
+    struct iovec iov;
+    uint8_t req[1];
+    ssize_t len;
+
+    cmsg = CMSG_FIRSTHDR(&msg);
+    cmsg->cmsg_level = SOL_SOCKET;
+    cmsg->cmsg_type = SCM_RIGHTS;
+    cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
+    msg.msg_controllen = cmsg->cmsg_len;
+
+    iov.iov_base = req;
+    iov.iov_len = sizeof(req);
+
+    msg.msg_iov = &iov;
+    msg.msg_iovlen = 1;
+
+    len = recvmsg(c, &msg, 0);
+    if (len > 0) {
+        memcpy(&fd, CMSG_DATA(cmsg), sizeof(fd));
+        return fd;
+    }
+
+    return len;
+}
+
+static int net_bridge_run_helper(const char *helper, const char *bridge)
+{
+    sigset_t oldmask, mask;
+    int pid, status;
+    char *args[5];
+    char **parg;
+    int sv[2];
+
+    sigemptyset(&mask);
+    sigaddset(&mask, SIGCHLD);
+    sigprocmask(SIG_BLOCK, &mask, &oldmask);
+
+    if (socketpair(PF_UNIX, SOCK_STREAM, 0, sv) == -1) {
+        return -1;
+    }
+
+    /* try to launch bridge helper */
+    pid = fork();
+    if (pid == 0) {
+        int open_max = sysconf(_SC_OPEN_MAX), i;
+        char buf[32];
+
+        snprintf(buf, sizeof(buf), "%d", sv[1]);
+
+        for (i = 0; i < open_max; i++) {
+            if (i != STDIN_FILENO &&
+                i != STDOUT_FILENO &&
+                i != STDERR_FILENO &&
+                i != sv[1]) {
+                close(i);
+            }
+        }
+        parg = args;
+        *parg++ = (char *)helper;
+        *parg++ = (char *)"--use-vnet";
+        *parg++ = (char *)bridge;
+        *parg++ = buf;
+        *parg++ = NULL;
+        execv(helper, args);
+        _exit(1);
+    } else if (pid > 0) {
+        int fd;
+
+        close(sv[1]);
+
+        do {
+            fd = recv_fd(sv[0]);
+        } while (fd == -1 && errno == EINTR);
+
+        close(sv[0]);
+
+        while (waitpid(pid, &status, 0) != pid) {
+            /* loop */
+        }
+        sigprocmask(SIG_SETMASK, &oldmask, NULL);
+        if (fd < 0) {
+            fprintf(stderr, "failed to recv file descriptor\n");
+            return -1;
+        }
+
+        if (WIFEXITED(status) && WEXITSTATUS(status) == 0) {
+            return fd;
+        }
+    }
+    fprintf(stderr, "failed to launch bridge helper\n");
+    return -1;
+}
+
+int net_init_bridge(QemuOpts *opts, Monitor *mon, const char *name,
+                    VLANState *vlan)
+{
+    TAPState *s;
+    int fd, vnet_hdr;
+
+    if (!qemu_opt_get(opts, "br")) {
+        qemu_opt_set(opts, "br", DEFAULT_BRIDGE_INTERFACE);
+    }
+    if (!qemu_opt_get(opts, "helper")) {
+        qemu_opt_set(opts, "helper", DEFAULT_BRIDGE_HELPER);
+    }
+
+    fd = net_bridge_run_helper(qemu_opt_get(opts, "helper"),
+                               qemu_opt_get(opts, "br"));
+    if (fd == -1) {
+        return -1;
+    }
+
+    fcntl(fd, F_SETFL, O_NONBLOCK);
+
+    vnet_hdr = tap_probe_vnet_hdr(fd);
+
+    s = net_tap_fd_init(vlan, "bridge", name, fd, vnet_hdr);
+    if (!s) {
+        close(fd);
+        return -1;
+    }
+
+    snprintf(s->nc.info_str, sizeof(s->nc.info_str),
+             "br=%s", qemu_opt_get(opts, "br"));
+
+    return 0;
+}
+
 static int net_tap_init(QemuOpts *opts, int *vnet_hdr)
 {
     int fd, vnet_hdr_required;
@@ -422,13 +559,17 @@  int net_init_tap(QemuOpts *opts, Monitor *mon, const char *name, VLANState *vlan
 {
     TAPState *s;
     int fd, vnet_hdr = 0;
+    const char *model;
 
     if (qemu_opt_get(opts, "fd")) {
         if (qemu_opt_get(opts, "ifname") ||
             qemu_opt_get(opts, "script") ||
             qemu_opt_get(opts, "downscript") ||
-            qemu_opt_get(opts, "vnet_hdr")) {
-            error_report("ifname=, script=, downscript= and vnet_hdr= is invalid with fd=");
+            qemu_opt_get(opts, "vnet_hdr") ||
+            qemu_opt_get(opts, "br") ||
+            qemu_opt_get(opts, "helper")) {
+            error_report("ifname=, script=, downscript=, vnet_hdr=, "
+                         "br= and helper= are invalid with fd=");
             return -1;
         }
 
@@ -440,7 +581,41 @@  int net_init_tap(QemuOpts *opts, Monitor *mon, const char *name, VLANState *vlan
         fcntl(fd, F_SETFL, O_NONBLOCK);
 
         vnet_hdr = tap_probe_vnet_hdr(fd);
+
+        model = "tap";
+
+    } else if (qemu_opt_get(opts, "helper")) {
+        if (qemu_opt_get(opts, "ifname") ||
+            qemu_opt_get(opts, "script") ||
+            qemu_opt_get(opts, "downscript") ||
+            qemu_opt_get(opts, "vnet_hdr")) {
+            error_report("ifname=, script=, downscript=, and vnet_hdr= "
+                         "are invalid with helper=");
+            return -1;
+        }
+
+        if (!qemu_opt_get(opts, "br")) {
+            qemu_opt_set(opts, "br", DEFAULT_BRIDGE_INTERFACE);
+        }
+
+        fd = net_bridge_run_helper(qemu_opt_get(opts, "helper"),
+                                   qemu_opt_get(opts, "br"));
+        if (fd == -1) {
+            return -1;
+        }
+
+        fcntl(fd, F_SETFL, O_NONBLOCK);
+
+        vnet_hdr = tap_probe_vnet_hdr(fd);
+
+        model = "bridge";
+
     } else {
+        if (qemu_opt_get(opts, "br")) {
+            error_report("br= is invalid with script=");
+            return -1;
+        }
+
         if (!qemu_opt_get(opts, "script")) {
             qemu_opt_set(opts, "script", DEFAULT_NETWORK_SCRIPT);
         }
@@ -453,9 +628,11 @@  int net_init_tap(QemuOpts *opts, Monitor *mon, const char *name, VLANState *vlan
         if (fd == -1) {
             return -1;
         }
+
+        model = "tap";
     }
 
-    s = net_tap_fd_init(vlan, "tap", name, fd, vnet_hdr);
+    s = net_tap_fd_init(vlan, model, name, fd, vnet_hdr);
     if (!s) {
         close(fd);
         return -1;
@@ -467,6 +644,10 @@  int net_init_tap(QemuOpts *opts, Monitor *mon, const char *name, VLANState *vlan
 
     if (qemu_opt_get(opts, "fd")) {
         snprintf(s->nc.info_str, sizeof(s->nc.info_str), "fd=%d", fd);
+    } else if (qemu_opt_get(opts, "helper")) {
+        snprintf(s->nc.info_str, sizeof(s->nc.info_str),
+                "helper=%s,br=%s", qemu_opt_get(opts, "helper"),
+                qemu_opt_get(opts, "br"));
     } else {
         const char *ifname, *script, *downscript;
 
diff --git a/net/tap.h b/net/tap.h
index e44bd2b..56c591f 100644
--- a/net/tap.h
+++ b/net/tap.h
@@ -57,4 +57,7 @@  int tap_get_fd(VLANClientState *vc);
 struct vhost_net;
 struct vhost_net *tap_get_vhost_net(VLANClientState *vc);
 
+int net_init_bridge(QemuOpts *opts, Monitor *mon, const char *name,
+                    VLANState *vlan);
+
 #endif /* QEMU_NET_TAP_H */
diff --git a/qemu-options.hx b/qemu-options.hx
index 087a3b9..4f2385d 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -1205,11 +1205,14 @@  DEF("net", HAS_ARG, QEMU_OPTION_net,
     "-net tap[,vlan=n][,name=str],ifname=name\n"
     "                connect the host TAP network interface to VLAN 'n'\n"
 #else
-    "-net tap[,vlan=n][,name=str][,fd=h][,ifname=name][,script=file][,downscript=dfile][,sndbuf=nbytes][,vnet_hdr=on|off][,vhost=on|off][,vhostfd=h][,vhostforce=on|off]\n"
-    "                connect the host TAP network interface to VLAN 'n' and use the\n"
-    "                network scripts 'file' (default=" DEFAULT_NETWORK_SCRIPT ")\n"
-    "                and 'dfile' (default=" DEFAULT_NETWORK_DOWN_SCRIPT ")\n"
+    "-net tap[,vlan=n][,name=str][,fd=h][,ifname=name][,script=file][,downscript=dfile][,br=bridge][,helper=helper][,sndbuf=nbytes][,vnet_hdr=on|off][,vhost=on|off][,vhostfd=h][,vhostforce=on|off]\n"
+    "                connect the host TAP network interface to VLAN 'n' \n"
+    "                use network scripts 'file' (default=" DEFAULT_NETWORK_SCRIPT ")\n"
+    "                to configure it and 'dfile' (default=" DEFAULT_NETWORK_DOWN_SCRIPT ")\n"
+    "                to deconfigure it\n"
     "                use '[down]script=no' to disable script execution\n"
+    "                use network helper 'helper' (default=" DEFAULT_BRIDGE_HELPER ") and\n"
+    "                bridge 'br' (default=" DEFAULT_BRIDGE_INTERFACE ") to configure it\n"
     "                use 'fd=h' to connect to an already opened TAP interface\n"
     "                use 'sndbuf=nbytes' to limit the size of the send buffer (the\n"
     "                default is disabled 'sndbuf=0' to enable flow control set 'sndbuf=1048576')\n"
@@ -1219,6 +1222,10 @@  DEF("net", HAS_ARG, QEMU_OPTION_net,
     "                    (only has effect for virtio guests which use MSIX)\n"
     "                use vhostforce=on to force vhost on for non-MSIX virtio guests\n"
     "                use 'vhostfd=h' to connect to an already opened vhost net device\n"
+    "-net bridge[,vlan=n][,name=str][,br=bridge][,helper=helper]\n"
+    "                connects a host TAP network interface to a host bridge device 'br'\n"
+    "                (default=" DEFAULT_BRIDGE_INTERFACE ") using the program 'helper'\n"
+    "                (default=" DEFAULT_BRIDGE_HELPER ")\n"
 #endif
     "-net socket[,vlan=n][,name=str][,fd=h][,listen=[host]:port][,connect=host:port]\n"
     "                connect the vlan 'n' to another VLAN using a socket connection\n"
@@ -1242,6 +1249,7 @@  DEF("netdev", HAS_ARG, QEMU_OPTION_netdev,
     "user|"
 #endif
     "tap|"
+    "bridge|"
 #ifdef CONFIG_VDE
     "vde|"
 #endif
@@ -1378,26 +1386,66 @@  processed and applied to -net user. Mixing them with the new configuration
 syntax gives undefined results. Their use for new applications is discouraged
 as they will be removed from future versions.
 
-@item -net tap[,vlan=@var{n}][,name=@var{name}][,fd=@var{h}][,ifname=@var{name}] [,script=@var{file}][,downscript=@var{dfile}]
-Connect the host TAP network interface @var{name} to VLAN @var{n}, use
-the network script @var{file} to configure it and the network script
+@item -net tap[,vlan=@var{n}][,name=@var{name}][,fd=@var{h}][,ifname=@var{name}][,script=@var{file}][,downscript=@var{dfile}][,br=@var{bridge}][,helper=@var{helper}]
+Connect the host TAP network interface @var{name} to VLAN @var{n}.
+
+Use the network script @var{file} to configure it and the network script
 @var{dfile} to deconfigure it. If @var{name} is not provided, the OS
-automatically provides one. @option{fd}=@var{h} can be used to specify
-the handle of an already opened host TAP interface. The default network
-configure script is @file{/etc/qemu-ifup} and the default network
-deconfigure script is @file{/etc/qemu-ifdown}. Use @option{script=no}
-or @option{downscript=no} to disable script execution. Example:
+automatically provides one. The default network configure script is
+@file{/etc/qemu-ifup} and the default network deconfigure script is
+@file{/etc/qemu-ifdown}. Use @option{script=no} or @option{downscript=no}
+to disable script execution.
+
+If running QEMU as an unprivileged user, use the network helper
+@var{helper} to configure the TAP interface. The default network
+helper executable is @file{/usr/local/libexec/qemu-bridge-helper}
+and the default bridge device is @file{br0}.
+
+@option{fd}=@var{h} can be used to specify the handle of an already
+opened host TAP interface.
+
+Examples:
 
 @example
+#launch a QEMU instance with the default network script
 qemu linux.img -net nic -net tap
 @end example
 
-More complicated example (two NICs, each one connected to a TAP device)
 @example
+#launch a QEMU instance with two NICs, each one connected
+#to a TAP device
 qemu linux.img -net nic,vlan=0 -net tap,vlan=0,ifname=tap0 \
                -net nic,vlan=1 -net tap,vlan=1,ifname=tap1
 @end example
 
+@example
+#launch a QEMU instance with the default network helper to
+#connect a TAP device to bridge br0
+qemu linux.img -net nic -net tap,helper=/usr/local/libexec/qemu-bridge-helper
+@end example
+
+@item -net bridge[,vlan=@var{n}][,name=@var{name}][,br=@var{bridge}][,helper=@var{helper}]
+Connect a host TAP network interface to a host bridge device.
+
+Use the network helper @var{helper} to configure the TAP interface and
+attach it to the bridge. The default network helper executable is
+@file{/usr/local/libexec/qemu-bridge-helper} and the default bridge
+device is @file{br0}.
+
+Examples:
+
+@example
+#launch a QEMU instance with the default network helper to
+#connect a TAP device to bridge br0
+qemu linux.img -net bridge -net nic,model=virtio
+@end example
+
+@example
+#launch a QEMU instance with the default network helper to
+#connect a TAP device to bridge qemubr0
+qemu linux.img -net bridge,br=qemubr0 -net nic,model=virtio
+@end example
+
 @item -net socket[,vlan=@var{n}][,name=@var{name}][,fd=@var{h}] [,listen=[@var{host}]:@var{port}][,connect=@var{host}:@var{port}]
 
 Connect the VLAN @var{n} to a remote VLAN in another QEMU virtual