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nbd: Support shorter handshake 

The NBD Protocol allows the server and client to mutually agree
on a shorter handshake (omit the 124 bytes of reserved 0), via
the server advertising NBD_FLAG_NO_ZEROES and the client
acknowledging with NBD_FLAG_C_NO_ZEROES (only possible in
newstyle, whether or not it is fixed newstyle).  It doesn't
shave much off the wire, but we might as well implement it.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Alex Bligh <alex@alex.org.uk>
Message-Id: <1476469998-28592-13-git-send-email-eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Eric Blake 2016-10-14 13:33:14 -05:00 committed by Paolo Bonzini
parent 75368aab9b
commit c203c59ad9
3 changed files with 22 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/block/nbd.h
View File

@ -74,11 +74,13 @@ typedef struct NBDReply NBDReply;
/* New-style handshake (global) flags, sent from server to client, and
control what will happen during handshake phase. */
#define NBD_FLAG_FIXED_NEWSTYLE (1 << 0) /* Fixed newstyle protocol. */
#define NBD_FLAG_FIXED_NEWSTYLE (1 << 0) /* Fixed newstyle protocol. */
#define NBD_FLAG_NO_ZEROES (1 << 1) /* End handshake without zeroes. */
/* New-style client flags, sent from client to server to control what happens
during handshake phase. */
#define NBD_FLAG_C_FIXED_NEWSTYLE (1 << 0) /* Fixed newstyle protocol. */
#define NBD_FLAG_C_FIXED_NEWSTYLE (1 << 0) /* Fixed newstyle protocol. */
#define NBD_FLAG_C_NO_ZEROES (1 << 1) /* End handshake without zeroes. */
/* Reply types. */
#define NBD_REP_ACK (1) /* Data sending finished. */

8
nbd/client.c
View File

@ -440,6 +440,7 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, uint16_t *flags,
char buf[256];
uint64_t magic, s;
int rc;
bool zeroes = true;
TRACE("Receiving negotiation tlscreds=%p hostname=%s.",
tlscreds, hostname ? hostname : "<null>");
@ -504,6 +505,11 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, uint16_t *flags,
TRACE("Server supports fixed new style");
clientflags |= NBD_FLAG_C_FIXED_NEWSTYLE;
}
if (globalflags & NBD_FLAG_NO_ZEROES) {
zeroes = false;
TRACE("Server supports no zeroes");
clientflags |= NBD_FLAG_C_NO_ZEROES;
}
/* client requested flags */
clientflags = cpu_to_be32(clientflags);
if (write_sync(ioc, &clientflags, sizeof(clientflags)) !=
@ -591,7 +597,7 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, uint16_t *flags,
}
TRACE("Size is %" PRIu64 ", export flags %" PRIx16, *size, *flags);
if (drop_sync(ioc, 124) != 124) {
if (zeroes && drop_sync(ioc, 124) != 124) {
error_setg(errp, "Failed to read reserved block");
goto fail;
}

15
nbd/server.c
View File

@ -81,6 +81,7 @@ struct NBDClient {
int refcount;
void (*close)(NBDClient *client);
bool no_zeroes;
NBDExport *exp;
QCryptoTLSCreds *tlscreds;
char *tlsaclname;
@ -450,6 +451,11 @@ static int nbd_negotiate_options(NBDClient *client)
fixedNewstyle = true;
flags &= ~NBD_FLAG_C_FIXED_NEWSTYLE;
}
if (flags & NBD_FLAG_C_NO_ZEROES) {
TRACE("Client supports no zeroes at handshake end");
client->no_zeroes = true;
flags &= ~NBD_FLAG_C_NO_ZEROES;
}
if (flags != 0) {
TRACE("Unknown client flags 0x%" PRIx32 " received", flags);
return -EIO;
@ -602,6 +608,7 @@ static coroutine_fn int nbd_negotiate(NBDClientNewData *data)
const uint16_t myflags = (NBD_FLAG_HAS_FLAGS | NBD_FLAG_SEND_TRIM |
NBD_FLAG_SEND_FLUSH | NBD_FLAG_SEND_FUA);
bool oldStyle;
size_t len;
/* Old style negotiation header without options
[ 0 .. 7] passwd ("NBDMAGIC")
@ -618,7 +625,7 @@ static coroutine_fn int nbd_negotiate(NBDClientNewData *data)
....options sent....
[18 .. 25] size
[26 .. 27] export flags
[28 .. 151] reserved (0)
[28 .. 151] reserved (0, omit if no_zeroes)
*/
qio_channel_set_blocking(client->ioc, false, NULL);
@ -637,7 +644,7 @@ static coroutine_fn int nbd_negotiate(NBDClientNewData *data)
stw_be_p(buf + 26, client->exp->nbdflags | myflags);
} else {
stq_be_p(buf + 8, NBD_OPTS_MAGIC);
stw_be_p(buf + 16, NBD_FLAG_FIXED_NEWSTYLE);
stw_be_p(buf + 16, NBD_FLAG_FIXED_NEWSTYLE | NBD_FLAG_NO_ZEROES);
}
if (oldStyle) {
@ -664,8 +671,8 @@ static coroutine_fn int nbd_negotiate(NBDClientNewData *data)
client->exp->size, client->exp->nbdflags | myflags);
stq_be_p(buf + 18, client->exp->size);
stw_be_p(buf + 26, client->exp->nbdflags | myflags);
if (nbd_negotiate_write(client->ioc, buf + 18, sizeof(buf) - 18) !=
sizeof(buf) - 18) {
len = client->no_zeroes ? 10 : sizeof(buf) - 18;
if (nbd_negotiate_write(client->ioc, buf + 18, len) != len) {
LOG("write failed");
goto fail;
}