Re: [Qemu-devel] [PATCH] Introduce NBD named exports.

[Laurent Vivier <Laurent@vivier.eu>]

Le mardi 24 août 2010 à 10:59 +0200, Kevin Wolf a écrit :
> Am 24.08.2010 03:04, 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>
> > ---
> >  block/nbd.c   |   57 +++++++++++++++++++--------
> >  nbd.c         |  119 ++++++++++++++++++++++++++++++++++++++++++++++++++------
> >  nbd.h         |    5 ++-
> >  qemu-doc.texi |    7 +++
> >  qemu-nbd.c    |    2 +-
> >  5 files changed, 158 insertions(+), 32 deletions(-)
> > 
> > diff --git a/block/nbd.c b/block/nbd.c
> > index a1ec123..ee22b47 100644
> > --- a/block/nbd.c
> > +++ b/block/nbd.c
> > @@ -42,55 +42,78 @@ typedef struct BDRVNBDState {
> >  static int nbd_open(BlockDriverState *bs, const char* filename, int flags)
> >  {
> >      BDRVNBDState *s = bs->opaque;
> > +
> > +    #define EN_OPTSTR ":exportname="
> 
> Hm, this makes EN_OPTSTR look like a local variable, but it's actually a
> macro which is valid after the end of the function. So maybe move it out?

I agree, but have a look at curl_open().

> 
> > +    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[sizeof(EN_OPTSTR) - 1] == 0)
> > +            goto out;
> 
> Please add braces here and throughout the patch (see CODING_STYLE)

OK.

> Maybe using strlen(EN_OPTSTR) would be clearer? At first I missed the
> fact that sizeof includes the null byte, but maybe it's just me.

I think sizeof() is resolved at compile time whereas strlen() it is at
runtime. For me, it is better, it like to have a constant.

> 
> > +        name[0] = 0;
> > +        name += sizeof(EN_OPTSTR) - 1;
> > +    }
> > +
> > +    if (!strstart(file, "nbd:", &host))
> > +        goto out;
> >  
> >      if (strstart(host, "unix:", &unixpath)) {
> >  
> >          if (unixpath[0] != '/')
> > -            return -EINVAL;
> > +            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++;
> >  
> > -        *p = '\0';
> > -        p++;
> > +            port = strtol(p, &r, 0);
> > +            if (r == p)
> > +                goto out;
> > +        } else if (name == NULL)
> > +                goto out;
> 
> Wrong indentation level (and missing braces again)

OK

> 
> >  
> > -        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, &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..755613a 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 +298,26 @@ 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,
> > +                          off_t *size, size_t *blocksize)
> >  {
> > -	char buf[8 + 8 + 8 + 128];
> > -	uint64_t magic;
> > +	char buf[256] = "\0\0\0\0\0\0\0\0\0";
> > +	uint64_t magic, s;
> > +	uint16_t tmp;
> > +	uint32_t flags;
> 
> Hm, where are the flags actually used? There are a few places where they
> are assigned, but I can't see any use.

It is never used. But as it is in the file, I take it. But I'll modify
the function to return flags as it is done in nbd-client (the reference
implementation).

> 
> >  
> >  	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;
> >  	}
> 
> I think this makes it easy to miss that you rely on getting null
> termination by the initialisation of buf. Why not do the obvious thing
> and just do a buf[8] = '\0' after the read?

because it is done like that in nbd-client.c... but I agree.

> 
> > -
> > -	magic = be64_to_cpup((uint64_t*)(buf + 8));
> > -	*size = be64_to_cpup((uint64_t*)(buf + 16));
> > -	*blocksize = 1024;
> > +	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 +328,6 @@ 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 +335,99 @@ 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 (magic != 0x00420281861253LL) {
> > -		LOG("Bad magic received");
> > +	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 (!name) {
> > +		if (read_sync(csock, &flags, sizeof(flags)) != sizeof(flags)) {
> > +			LOG("read failed (flags)");
> > +			errno = EINVAL;
> > +			return -1;
> > +		}
> > +		flags = be64_to_cpu(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..17be0fa 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,
> > +                          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..ca5bf53 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
> 
> Please remove the space before the comma.

OK

> I don't have a new enough ndbserver to test if it actually works (and I

You can test against an old nbdserver to check it is always working ;-)
(or qemu-nbd).

> also haven't checked the spec for the new parts), so I'll have to trust
> your tests there.

There is no spec (what is a spec ;-) ?), only a reference implementation
in nbd-client.c and nbd-server.c from http://nbd.sf.net.

Thank you for the review.

Patch follows nearly...

> 
> Kevin

Laurent
-- 
--------------------- laurent@vivier.eu ----------------------
"Tout ce qui est impossible reste à accomplir"    Jules Verne
"Things are only impossible until they're not" Jean-Luc Picard