Patchwork [v3] Introduce NBD named exports.

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Submitter Laurent Vivier
Date Aug. 25, 2010, 8:48 p.m.
Message ID <1282769313-25061-1-git-send-email-laurent@vivier.eu>
Download mbox | patch
Permalink /patch/62733/
State New
Headers show

Comments

Laurent Vivier - Aug. 25, 2010, 8:48 p.m.
This patch allows to connect Qemu using NBD protocol to an nbd-server
using named exports.

For instance, if on the host "isoserver", in /etc/nbd-server/config, you have:

[generic]
[debian-500-ppc-netinst]
        exportname = /ISO/debian-500-powerpc-netinst.iso
[Fedora-10-ppc-netinst]
        exportname = /ISO/Fedora-10-ppc-netinst.iso

You can connect to it, using:

    qemu -cdrom nbd:isoserver:exportname=debian-500-ppc-netinst
    qemu -cdrom nbd:isoserver:exportname=Fedora-10-ppc-netinst

NOTE: you need at least nbd-server 2.9.18

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
---
v3: change sizeof() by strlen()
v2: address Kevin comments (CODING STYLE)

 block/nbd.c   |   68 +++++++++++++++++++++++---------
 nbd.c         |  118 +++++++++++++++++++++++++++++++++++++++++++++++++++------
 nbd.h         |    5 ++-
 qemu-doc.texi |    7 +++
 qemu-nbd.c    |    4 +-
 5 files changed, 169 insertions(+), 33 deletions(-)
Anthony Liguori - Aug. 25, 2010, 9:10 p.m.
On 08/25/2010 03:48 PM, Laurent Vivier wrote:
> This patch allows to connect Qemu using NBD protocol to an nbd-server
> using named exports.
>    

Does using a named export make the NBD protocol incompatible with a 
server that doesn't support named exports?  IOW, it's essentially a new 
protocol layered underneath of NBD?

Regards,

Anthony Liguori

> For instance, if on the host "isoserver", in /etc/nbd-server/config, you have:
>
> [generic]
> [debian-500-ppc-netinst]
>          exportname = /ISO/debian-500-powerpc-netinst.iso
> [Fedora-10-ppc-netinst]
>          exportname = /ISO/Fedora-10-ppc-netinst.iso
>
> You can connect to it, using:
>
>      qemu -cdrom nbd:isoserver:exportname=debian-500-ppc-netinst
>      qemu -cdrom nbd:isoserver:exportname=Fedora-10-ppc-netinst
>
> NOTE: you need at least nbd-server 2.9.18
>
> Signed-off-by: Laurent Vivier<laurent@vivier.eu>
> ---
> v3: change sizeof() by strlen()
> v2: address Kevin comments (CODING STYLE)
>
>   block/nbd.c   |   68 +++++++++++++++++++++++---------
>   nbd.c         |  118 +++++++++++++++++++++++++++++++++++++++++++++++++++------
>   nbd.h         |    5 ++-
>   qemu-doc.texi |    7 +++
>   qemu-nbd.c    |    4 +-
>   5 files changed, 169 insertions(+), 33 deletions(-)
>
> diff --git a/block/nbd.c b/block/nbd.c
> index a1ec123..5e9d6cb 100644
> --- a/block/nbd.c
> +++ b/block/nbd.c
> @@ -33,6 +33,8 @@
>   #include<sys/types.h>
>   #include<unistd.h>
>
> +#define EN_OPTSTR ":exportname="
> +
>   typedef struct BDRVNBDState {
>       int sock;
>       off_t size;
> @@ -42,55 +44,83 @@ typedef struct BDRVNBDState {
>   static int nbd_open(BlockDriverState *bs, const char* filename, int flags)
>   {
>       BDRVNBDState *s = bs->opaque;
> +    uint32_t nbdflags;
> +
> +    char *file;
> +    char *name;
>       const char *host;
>       const char *unixpath;
>       int sock;
>       off_t size;
>       size_t blocksize;
>       int ret;
> +    int err = -EINVAL;
> +
> +    file = qemu_strdup(filename);
>
> -    if (!strstart(filename, "nbd:",&host))
> -        return -EINVAL;
> +    name = strstr(file, EN_OPTSTR);
> +    if (name) {
> +        if (name[strlen(EN_OPTSTR)] == 0) {
> +            goto out;
> +        }
> +        name[0] = 0;
> +        name += strlen(EN_OPTSTR);
> +    }
> +
> +    if (!strstart(file, "nbd:",&host)) {
> +        goto out;
> +    }
>
>       if (strstart(host, "unix:",&unixpath)) {
>
> -        if (unixpath[0] != '/')
> -            return -EINVAL;
> +        if (unixpath[0] != '/') {
> +            goto out;
> +        }
>
>           sock = unix_socket_outgoing(unixpath);
>
>       } else {
> -        uint16_t port;
> +        uint16_t port = NBD_DEFAULT_PORT;
>           char *p, *r;
>           char hostname[128];
>
>           pstrcpy(hostname, 128, host);
>
>           p = strchr(hostname, ':');
> -        if (p == NULL)
> -            return -EINVAL;
> +        if (p != NULL) {
> +            *p = '\0';
> +            p++;
> +
> +            port = strtol(p,&r, 0);
> +            if (r == p) {
> +                goto out;
> +            }
> +        } else if (name == NULL) {
> +            goto out;
> +        }
>
> -        *p = '\0';
> -        p++;
> -
> -        port = strtol(p,&r, 0);
> -        if (r == p)
> -            return -EINVAL;
>           sock = tcp_socket_outgoing(hostname, port);
>       }
>
> -    if (sock == -1)
> -        return -errno;
> +    if (sock == -1) {
> +        err = -errno;
> +        goto out;
> +    }
>
> -    ret = nbd_receive_negotiate(sock,&size,&blocksize);
> -    if (ret == -1)
> -        return -errno;
> +    ret = nbd_receive_negotiate(sock, name,&nbdflags,&size,&blocksize);
> +    if (ret == -1) {
> +        err = -errno;
> +        goto out;
> +    }
>
>       s->sock = sock;
>       s->size = size;
>       s->blocksize = blocksize;
> +    err = 0;
>
> -    return 0;
> +out:
> +    qemu_free(file);
> +    return err;
>   }
>
>   static int nbd_read(BlockDriverState *bs, int64_t sector_num,
> diff --git a/nbd.c b/nbd.c
> index a9f295f..30dec8d 100644
> --- a/nbd.c
> +++ b/nbd.c
> @@ -62,6 +62,8 @@
>   #define NBD_SET_SIZE_BLOCKS	_IO(0xab, 7)
>   #define NBD_DISCONNECT          _IO(0xab, 8)
>
> +#define NBD_OPT_EXPORT_NAME	(1<<  0)
> +
>   /* That's all folks */
>
>   #define read_sync(fd, buffer, size) nbd_wr_sync(fd, buffer, size, true)
> @@ -296,22 +298,27 @@ int nbd_negotiate(int csock, off_t size)
>   	return 0;
>   }
>
> -int nbd_receive_negotiate(int csock, off_t *size, size_t *blocksize)
> +int nbd_receive_negotiate(int csock, const char *name, uint32_t *flags,
> +                          off_t *size, size_t *blocksize)
>   {
> -	char buf[8 + 8 + 8 + 128];
> -	uint64_t magic;
> +	char buf[256];
> +	uint64_t magic, s;
> +	uint16_t tmp;
>
>   	TRACE("Receiving negotation.");
>
> -	if (read_sync(csock, buf, sizeof(buf)) != sizeof(buf)) {
> +	if (read_sync(csock, buf, 8) != 8) {
>   		LOG("read failed");
>   		errno = EINVAL;
>   		return -1;
>   	}
>
> -	magic = be64_to_cpup((uint64_t*)(buf + 8));
> -	*size = be64_to_cpup((uint64_t*)(buf + 16));
> -	*blocksize = 1024;
> +	buf[8] = '\0';
> +	if (strlen(buf) == 0) {
> +		LOG("server connection closed");
> +		errno = EINVAL;
> +		return -1;
> +	}
>
>   	TRACE("Magic is %c%c%c%c%c%c%c%c",
>   	      qemu_isprint(buf[0]) ? buf[0] : '.',
> @@ -322,8 +329,6 @@ int nbd_receive_negotiate(int csock, off_t *size, size_t *blocksize)
>   	      qemu_isprint(buf[5]) ? buf[5] : '.',
>   	      qemu_isprint(buf[6]) ? buf[6] : '.',
>   	      qemu_isprint(buf[7]) ? buf[7] : '.');
> -	TRACE("Magic is 0x%" PRIx64, magic);
> -	TRACE("Size is %" PRIu64, *size);
>
>   	if (memcmp(buf, "NBDMAGIC", 8) != 0) {
>   		LOG("Invalid magic received");
> @@ -331,10 +336,99 @@ int nbd_receive_negotiate(int csock, off_t *size, size_t *blocksize)
>   		return -1;
>   	}
>
> -	TRACE("Checking magic");
> +	if (read_sync(csock,&magic, sizeof(magic)) != sizeof(magic)) {
> +		LOG("read failed");
> +		errno = EINVAL;
> +		return -1;
> +	}
> +	magic = be64_to_cpu(magic);
> +	TRACE("Magic is 0x%" PRIx64, magic);
> +
> +	if (name) {
> +		uint32_t reserved = 0;
> +		uint32_t opt;
> +		uint32_t namesize;
> +
> +		TRACE("Checking magic (opts_magic)");
> +		if (magic != 0x49484156454F5054LL) {
> +			LOG("Bad magic received");
> +			errno = EINVAL;
> +			return -1;
> +		}
> +		if (read_sync(csock,&tmp, sizeof(tmp)) != sizeof(tmp)) {
> +			LOG("flags read failed");
> +			errno = EINVAL;
> +			return -1;
> +		}
> +		*flags = be16_to_cpu(tmp)<<  16;
> +		/* reserved for future use */
> +		if (write_sync(csock,&reserved, sizeof(reserved)) !=
> +		    sizeof(reserved)) {
> +			LOG("write failed (reserved)");
> +			errno = EINVAL;
> +			return -1;
> +		}
> +		/* write the export name */
> +		magic = cpu_to_be64(magic);
> +		if (write_sync(csock,&magic, sizeof(magic)) != sizeof(magic)) {
> +			LOG("write failed (magic)");
> +			errno = EINVAL;
> +			return -1;
> +		}
> +		opt = cpu_to_be32(NBD_OPT_EXPORT_NAME);
> +		if (write_sync(csock,&opt, sizeof(opt)) != sizeof(opt)) {
> +			LOG("write failed (opt)");
> +			errno = EINVAL;
> +			return -1;
> +		}
> +		namesize = cpu_to_be32(strlen(name));
> +		if (write_sync(csock,&namesize, sizeof(namesize)) !=
> +		    sizeof(namesize)) {
> +			LOG("write failed (namesize)");
> +			errno = EINVAL;
> +			return -1;
> +		}
> +		if (write_sync(csock, (char*)name, strlen(name)) != strlen(name)) {
> +			LOG("write failed (name)");
> +			errno = EINVAL;
> +			return -1;
> +		}
> +	} else {
> +		TRACE("Checking magic (cli_magic)");
> +
> +		if (magic != 0x00420281861253LL) {
> +			LOG("Bad magic received");
> +			errno = EINVAL;
> +			return -1;
> +		}
> +	}
> +
> +	if (read_sync(csock,&s, sizeof(s)) != sizeof(s)) {
> +		LOG("read failed");
> +		errno = EINVAL;
> +		return -1;
> +	}
> +	*size = be64_to_cpu(s);
> +	*blocksize = 1024;
> +	TRACE("Size is %" PRIu64, *size);
>
> -	if (magic != 0x00420281861253LL) {
> -		LOG("Bad magic received");
> +	if (!name) {
> +		if (read_sync(csock, flags, sizeof(*flags)) != sizeof(*flags)) {
> +			LOG("read failed (flags)");
> +			errno = EINVAL;
> +			return -1;
> +		}
> +		*flags = be32_to_cpup(flags);
> +	} else {
> +		if (read_sync(csock,&tmp, sizeof(tmp)) != sizeof(tmp)) {
> +			LOG("read failed (tmp)");
> +			errno = EINVAL;
> +			return -1;
> +		}
> +		*flags |= be32_to_cpu(tmp);
> +	}
> +	if (read_sync(csock,&buf, 124) != 124) {
> +		LOG("read failed (buf)");
>   		errno = EINVAL;
>   		return -1;
>   	}
> diff --git a/nbd.h b/nbd.h
> index 5a1fbdf..8ff65a1 100644
> --- a/nbd.h
> +++ b/nbd.h
> @@ -42,6 +42,8 @@ enum {
>       NBD_CMD_DISC = 2
>   };
>
> +#define NBD_DEFAULT_PORT	10809
> +
>   size_t nbd_wr_sync(int fd, void *buffer, size_t size, bool do_read);
>   int tcp_socket_outgoing(const char *address, uint16_t port);
>   int tcp_socket_incoming(const char *address, uint16_t port);
> @@ -49,7 +51,8 @@ int unix_socket_outgoing(const char *path);
>   int unix_socket_incoming(const char *path);
>
>   int nbd_negotiate(int csock, off_t size);
> -int nbd_receive_negotiate(int csock, off_t *size, size_t *blocksize);
> +int nbd_receive_negotiate(int csock, const char *name, uint32_t *flags,
> +                          off_t *size, size_t *blocksize);
>   int nbd_init(int fd, int csock, off_t size, size_t blocksize);
>   int nbd_send_request(int csock, struct nbd_request *request);
>   int nbd_receive_reply(int csock, struct nbd_reply *reply);
> diff --git a/qemu-doc.texi b/qemu-doc.texi
> index 55a966f..d7d760f 100644
> --- a/qemu-doc.texi
> +++ b/qemu-doc.texi
> @@ -620,6 +620,13 @@ qemu linux1.img -hdb nbd:unix:/tmp/my_socket
>   qemu linux2.img -hdb nbd:unix:/tmp/my_socket
>   @end example
>
> +If the nbd-server uses named exports (since NBD 2.9.18), you must use the
> +"exportname" option:
> +@example
> +qemu -cdrom nbd:localhost:exportname=debian-500-ppc-netinst
> +qemu -cdrom nbd:localhost:exportname=openSUSE-11.1-ppc-netinst
> +@end example
> +
>   @node pcsys_network
>   @section Network emulation
>
> diff --git a/qemu-nbd.c b/qemu-nbd.c
> index 4e607cf..41e5c5d 100644
> --- a/qemu-nbd.c
> +++ b/qemu-nbd.c
> @@ -230,6 +230,7 @@ int main(int argc, char **argv)
>       int nb_fds = 0;
>       int max_fd;
>       int persistent = 0;
> +    uint32_t nbdflags;
>
>       while ((ch = getopt_long(argc, argv, sopt, lopt,&opt_ind)) != -1) {
>           switch (ch) {
> @@ -398,7 +399,8 @@ int main(int argc, char **argv)
>                   goto out;
>               }
>
> -            ret = nbd_receive_negotiate(sock,&size,&blocksize);
> +            ret = nbd_receive_negotiate(sock, NULL,&nbdflags,
> +					&size,&blocksize);
>               if (ret == -1) {
>                   ret = 1;
>                   goto out;
>
Kevin Wolf - Aug. 26, 2010, 2:07 p.m.
Am 25.08.2010 22:48, schrieb Laurent Vivier:
> This patch allows to connect Qemu using NBD protocol to an nbd-server
> using named exports.
> 
> For instance, if on the host "isoserver", in /etc/nbd-server/config, you have:
> 
> [generic]
> [debian-500-ppc-netinst]
>         exportname = /ISO/debian-500-powerpc-netinst.iso
> [Fedora-10-ppc-netinst]
>         exportname = /ISO/Fedora-10-ppc-netinst.iso
> 
> You can connect to it, using:
> 
>     qemu -cdrom nbd:isoserver:exportname=debian-500-ppc-netinst
>     qemu -cdrom nbd:isoserver:exportname=Fedora-10-ppc-netinst
> 
> NOTE: you need at least nbd-server 2.9.18
> 
> Signed-off-by: Laurent Vivier <laurent@vivier.eu>

Thanks, applied to the block branch.

Kevin

Patch

diff --git a/block/nbd.c b/block/nbd.c
index a1ec123..5e9d6cb 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -33,6 +33,8 @@ 
 #include <sys/types.h>
 #include <unistd.h>
 
+#define EN_OPTSTR ":exportname="
+
 typedef struct BDRVNBDState {
     int sock;
     off_t size;
@@ -42,55 +44,83 @@  typedef struct BDRVNBDState {
 static int nbd_open(BlockDriverState *bs, const char* filename, int flags)
 {
     BDRVNBDState *s = bs->opaque;
+    uint32_t nbdflags;
+
+    char *file;
+    char *name;
     const char *host;
     const char *unixpath;
     int sock;
     off_t size;
     size_t blocksize;
     int ret;
+    int err = -EINVAL;
+
+    file = qemu_strdup(filename);
 
-    if (!strstart(filename, "nbd:", &host))
-        return -EINVAL;
+    name = strstr(file, EN_OPTSTR);
+    if (name) {
+        if (name[strlen(EN_OPTSTR)] == 0) {
+            goto out;
+        }
+        name[0] = 0;
+        name += strlen(EN_OPTSTR);
+    }
+
+    if (!strstart(file, "nbd:", &host)) {
+        goto out;
+    }
 
     if (strstart(host, "unix:", &unixpath)) {
 
-        if (unixpath[0] != '/')
-            return -EINVAL;
+        if (unixpath[0] != '/') {
+            goto out;
+        }
 
         sock = unix_socket_outgoing(unixpath);
 
     } else {
-        uint16_t port;
+        uint16_t port = NBD_DEFAULT_PORT;
         char *p, *r;
         char hostname[128];
 
         pstrcpy(hostname, 128, host);
 
         p = strchr(hostname, ':');
-        if (p == NULL)
-            return -EINVAL;
+        if (p != NULL) {
+            *p = '\0';
+            p++;
+
+            port = strtol(p, &r, 0);
+            if (r == p) {
+                goto out;
+            }
+        } else if (name == NULL) {
+            goto out;
+        }
 
-        *p = '\0';
-        p++;
-
-        port = strtol(p, &r, 0);
-        if (r == p)
-            return -EINVAL;
         sock = tcp_socket_outgoing(hostname, port);
     }
 
-    if (sock == -1)
-        return -errno;
+    if (sock == -1) {
+        err = -errno;
+        goto out;
+    }
 
-    ret = nbd_receive_negotiate(sock, &size, &blocksize);
-    if (ret == -1)
-        return -errno;
+    ret = nbd_receive_negotiate(sock, name, &nbdflags, &size, &blocksize);
+    if (ret == -1) {
+        err = -errno;
+        goto out;
+    }
 
     s->sock = sock;
     s->size = size;
     s->blocksize = blocksize;
+    err = 0;
 
-    return 0;
+out:
+    qemu_free(file);
+    return err;
 }
 
 static int nbd_read(BlockDriverState *bs, int64_t sector_num,
diff --git a/nbd.c b/nbd.c
index a9f295f..30dec8d 100644
--- a/nbd.c
+++ b/nbd.c
@@ -62,6 +62,8 @@ 
 #define NBD_SET_SIZE_BLOCKS	_IO(0xab, 7)
 #define NBD_DISCONNECT          _IO(0xab, 8)
 
+#define NBD_OPT_EXPORT_NAME	(1 << 0)
+
 /* That's all folks */
 
 #define read_sync(fd, buffer, size) nbd_wr_sync(fd, buffer, size, true)
@@ -296,22 +298,27 @@  int nbd_negotiate(int csock, off_t size)
 	return 0;
 }
 
-int nbd_receive_negotiate(int csock, off_t *size, size_t *blocksize)
+int nbd_receive_negotiate(int csock, const char *name, uint32_t *flags,
+                          off_t *size, size_t *blocksize)
 {
-	char buf[8 + 8 + 8 + 128];
-	uint64_t magic;
+	char buf[256];
+	uint64_t magic, s;
+	uint16_t tmp;
 
 	TRACE("Receiving negotation.");
 
-	if (read_sync(csock, buf, sizeof(buf)) != sizeof(buf)) {
+	if (read_sync(csock, buf, 8) != 8) {
 		LOG("read failed");
 		errno = EINVAL;
 		return -1;
 	}
 
-	magic = be64_to_cpup((uint64_t*)(buf + 8));
-	*size = be64_to_cpup((uint64_t*)(buf + 16));
-	*blocksize = 1024;
+	buf[8] = '\0';
+	if (strlen(buf) == 0) {
+		LOG("server connection closed");
+		errno = EINVAL;
+		return -1;
+	}
 
 	TRACE("Magic is %c%c%c%c%c%c%c%c",
 	      qemu_isprint(buf[0]) ? buf[0] : '.',
@@ -322,8 +329,6 @@  int nbd_receive_negotiate(int csock, off_t *size, size_t *blocksize)
 	      qemu_isprint(buf[5]) ? buf[5] : '.',
 	      qemu_isprint(buf[6]) ? buf[6] : '.',
 	      qemu_isprint(buf[7]) ? buf[7] : '.');
-	TRACE("Magic is 0x%" PRIx64, magic);
-	TRACE("Size is %" PRIu64, *size);
 
 	if (memcmp(buf, "NBDMAGIC", 8) != 0) {
 		LOG("Invalid magic received");
@@ -331,10 +336,99 @@  int nbd_receive_negotiate(int csock, off_t *size, size_t *blocksize)
 		return -1;
 	}
 
-	TRACE("Checking magic");
+	if (read_sync(csock, &magic, sizeof(magic)) != sizeof(magic)) {
+		LOG("read failed");
+		errno = EINVAL;
+		return -1;
+	}
+	magic = be64_to_cpu(magic);
+	TRACE("Magic is 0x%" PRIx64, magic);
+
+	if (name) {
+		uint32_t reserved = 0;
+		uint32_t opt;
+		uint32_t namesize;
+
+		TRACE("Checking magic (opts_magic)");
+		if (magic != 0x49484156454F5054LL) {
+			LOG("Bad magic received");
+			errno = EINVAL;
+			return -1;
+		}
+		if (read_sync(csock, &tmp, sizeof(tmp)) != sizeof(tmp)) {
+			LOG("flags read failed");
+			errno = EINVAL;
+			return -1;
+		}
+		*flags = be16_to_cpu(tmp) << 16;
+		/* reserved for future use */
+		if (write_sync(csock, &reserved, sizeof(reserved)) !=
+		    sizeof(reserved)) {
+			LOG("write failed (reserved)");
+			errno = EINVAL;
+			return -1;
+		}
+		/* write the export name */
+		magic = cpu_to_be64(magic);
+		if (write_sync(csock, &magic, sizeof(magic)) != sizeof(magic)) {
+			LOG("write failed (magic)");
+			errno = EINVAL;
+			return -1;
+		}
+		opt = cpu_to_be32(NBD_OPT_EXPORT_NAME);
+		if (write_sync(csock, &opt, sizeof(opt)) != sizeof(opt)) {
+			LOG("write failed (opt)");
+			errno = EINVAL;
+			return -1;
+		}
+		namesize = cpu_to_be32(strlen(name));
+		if (write_sync(csock, &namesize, sizeof(namesize)) !=
+		    sizeof(namesize)) {
+			LOG("write failed (namesize)");
+			errno = EINVAL;
+			return -1;
+		}
+		if (write_sync(csock, (char*)name, strlen(name)) != strlen(name)) {
+			LOG("write failed (name)");
+			errno = EINVAL;
+			return -1;
+		}
+	} else {
+		TRACE("Checking magic (cli_magic)");
+
+		if (magic != 0x00420281861253LL) {
+			LOG("Bad magic received");
+			errno = EINVAL;
+			return -1;
+		}
+	}
+
+	if (read_sync(csock, &s, sizeof(s)) != sizeof(s)) {
+		LOG("read failed");
+		errno = EINVAL;
+		return -1;
+	}
+	*size = be64_to_cpu(s);
+	*blocksize = 1024;
+	TRACE("Size is %" PRIu64, *size);
 
-	if (magic != 0x00420281861253LL) {
-		LOG("Bad magic received");
+	if (!name) {
+		if (read_sync(csock, flags, sizeof(*flags)) != sizeof(*flags)) {
+			LOG("read failed (flags)");
+			errno = EINVAL;
+			return -1;
+		}
+		*flags = be32_to_cpup(flags);
+	} else {
+		if (read_sync(csock, &tmp, sizeof(tmp)) != sizeof(tmp)) {
+			LOG("read failed (tmp)");
+			errno = EINVAL;
+			return -1;
+		}
+		*flags |= be32_to_cpu(tmp);
+	}
+	if (read_sync(csock, &buf, 124) != 124) {
+		LOG("read failed (buf)");
 		errno = EINVAL;
 		return -1;
 	}
diff --git a/nbd.h b/nbd.h
index 5a1fbdf..8ff65a1 100644
--- a/nbd.h
+++ b/nbd.h
@@ -42,6 +42,8 @@  enum {
     NBD_CMD_DISC = 2
 };
 
+#define NBD_DEFAULT_PORT	10809
+
 size_t nbd_wr_sync(int fd, void *buffer, size_t size, bool do_read);
 int tcp_socket_outgoing(const char *address, uint16_t port);
 int tcp_socket_incoming(const char *address, uint16_t port);
@@ -49,7 +51,8 @@  int unix_socket_outgoing(const char *path);
 int unix_socket_incoming(const char *path);
 
 int nbd_negotiate(int csock, off_t size);
-int nbd_receive_negotiate(int csock, off_t *size, size_t *blocksize);
+int nbd_receive_negotiate(int csock, const char *name, uint32_t *flags,
+                          off_t *size, size_t *blocksize);
 int nbd_init(int fd, int csock, off_t size, size_t blocksize);
 int nbd_send_request(int csock, struct nbd_request *request);
 int nbd_receive_reply(int csock, struct nbd_reply *reply);
diff --git a/qemu-doc.texi b/qemu-doc.texi
index 55a966f..d7d760f 100644
--- a/qemu-doc.texi
+++ b/qemu-doc.texi
@@ -620,6 +620,13 @@  qemu linux1.img -hdb nbd:unix:/tmp/my_socket
 qemu linux2.img -hdb nbd:unix:/tmp/my_socket
 @end example
 
+If the nbd-server uses named exports (since NBD 2.9.18), you must use the
+"exportname" option:
+@example
+qemu -cdrom nbd:localhost:exportname=debian-500-ppc-netinst
+qemu -cdrom nbd:localhost:exportname=openSUSE-11.1-ppc-netinst
+@end example
+
 @node pcsys_network
 @section Network emulation
 
diff --git a/qemu-nbd.c b/qemu-nbd.c
index 4e607cf..41e5c5d 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -230,6 +230,7 @@  int main(int argc, char **argv)
     int nb_fds = 0;
     int max_fd;
     int persistent = 0;
+    uint32_t nbdflags;
 
     while ((ch = getopt_long(argc, argv, sopt, lopt, &opt_ind)) != -1) {
         switch (ch) {
@@ -398,7 +399,8 @@  int main(int argc, char **argv)
                 goto out;
             }
 
-            ret = nbd_receive_negotiate(sock, &size, &blocksize);
+            ret = nbd_receive_negotiate(sock, NULL, &nbdflags,
+					&size, &blocksize);
             if (ret == -1) {
                 ret = 1;
                 goto out;