Patchwork slirp: add 'cmd:' target for guestfwd

When using guestfwd=, Qemu only connects the virtual server's TCP port
to a single chardev. This is useless in most cases, as we usually want
to have more than a single connection from the guest to the outside world.

This patch adds a new cmd: target to guestfwd= that allows for execution
of a command on every TCP connection. This leverages the same code as
the -smb parameter, just that here the command is user defined.

Reported-by: Sascha Wilde <wilde@intevation.de>
Signed-off-by: Alexander Graf <agraf@suse.de>

---

v1 -> v2:

  - rebase to current master
  - fix documentation
---
 net/slirp.c     |   44 +++++++++++++++++++++++++++-----------------
 qemu-options.hx |   22 +++++++++++++++++++++-
 2 files changed, 48 insertions(+), 18 deletions(-)

On 2012-06-03 09:45, Alexander Graf wrote:
> When using guestfwd=, Qemu only connects the virtual server's TCP port
> to a single chardev. This is useless in most cases, as we usually want
> to have more than a single connection from the guest to the outside world.
> 
> This patch adds a new cmd: target to guestfwd= that allows for execution
> of a command on every TCP connection. This leverages the same code as
> the -smb parameter, just that here the command is user defined.
> 
> Reported-by: Sascha Wilde <wilde@intevation.de>
> Signed-off-by: Alexander Graf <agraf@suse.de>
> 
> ---
> 
> v1 -> v2:
> 
>   - rebase to current master
>   - fix documentation
> ---
>  net/slirp.c     |   44 +++++++++++++++++++++++++++-----------------
>  qemu-options.hx |   22 +++++++++++++++++++++-
>  2 files changed, 48 insertions(+), 18 deletions(-)
> 
> diff --git a/net/slirp.c b/net/slirp.c
> index 96f5032..41cd058 100644
> --- a/net/slirp.c
> +++ b/net/slirp.c
> @@ -616,25 +616,35 @@ static int slirp_guestfwd(SlirpState *s, const char *config_str,
>  
>      fwd = g_malloc(sizeof(struct GuestFwd));
>      snprintf(buf, sizeof(buf), "guestfwd.tcp.%d", port);
> -    fwd->hd = qemu_chr_new(buf, p, NULL);
> -    if (!fwd->hd) {
> -        error_report("could not open guest forwarding device '%s'", buf);
> -        g_free(fwd);
> -        return -1;
> -    }
>  
> -    if (slirp_add_exec(s->slirp, 3, fwd->hd, &server, port) < 0) {
> -        error_report("conflicting/invalid host:port in guest forwarding "
> -                     "rule '%s'", config_str);
> -        g_free(fwd);
> -        return -1;
> -    }
> -    fwd->server = server;
> -    fwd->port = port;
> -    fwd->slirp = s->slirp;
> +    if ((strlen(p) > 4) && !strncmp(p, "cmd:", 4)) {
> +        if (slirp_add_exec(s->slirp, 0, &p[4], &server, port) < 0) {
> +            error_report("conflicting/invalid host:port in guest forwarding "
> +                         "rule '%s'", config_str);
> +            g_free(fwd);
> +            return -1;
> +        }
> +    } else {
> +        fwd->hd = qemu_chr_new(buf, p, NULL);
> +        if (!fwd->hd) {
> +            error_report("could not open guest forwarding device '%s'", buf);
> +            g_free(fwd);
> +            return -1;
> +        }
> +
> +        if (slirp_add_exec(s->slirp, 3, fwd->hd, &server, port) < 0) {
> +            error_report("conflicting/invalid host:port in guest forwarding "
> +                         "rule '%s'", config_str);
> +            g_free(fwd);
> +            return -1;
> +        }
> +        fwd->server = server;
> +        fwd->port = port;
> +        fwd->slirp = s->slirp;
>  
> -    qemu_chr_add_handlers(fwd->hd, guestfwd_can_read, guestfwd_read,
> -                          NULL, fwd);
> +        qemu_chr_add_handlers(fwd->hd, guestfwd_can_read, guestfwd_read,
> +                              NULL, fwd);
> +    }
>      return 0;
>  
>   fail_syntax:
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 8b66264..ecf7ca1 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -1421,8 +1421,28 @@ Then when you use on the host @code{telnet localhost 5555}, you
>  connect to the guest telnet server.
>  
>  @item guestfwd=[tcp]:@var{server}:@var{port}-@var{dev}
> +@item guestfwd=[tcp]:@var{server}:@var{port}-@var{cmd:command}
>  Forward guest TCP connections to the IP address @var{server} on port @var{port}
> -to the character device @var{dev}. This option can be given multiple times.
> +to the character device @var{dev} or to a program executed by @var{cmd:command}
> +which gets spawned for each connection. This option can be given multiple times.
> +
> +You can either use a chardev directly and have that one used throughout Qemu's
> +lifetime, like in the following example:
> +
> +@example
> +# open 10.10.1.1:4321 on bootup, connect 10.0.2.100:1234 to it whenever
> +# the guest accesses it
> +qemu -net user,guestfwd=tcp:10.0.2.100:1234-tcp:10.10.1.1:4321 [...]
> +@end example
> +
> +Or you can execute a command on every TCP connection established by the guest,
> +so that Qemu behaves similar to an inetd process for that virtual server:
> +
> +@example
> +# call "netcat 10.10.1.1 4321" on every TCP connection to 10.0.2.100:1234
> +# and connect the TCP stream to its stdin/stdout
> +qemu -net 'user,guestfwd=tcp:10.0.2.100:1234-cmd:netcat 10.10.1.1 4321'
> +@end example
>  
>  @end table
>  
> 

Thanks, queued.

Jan