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 <ebl...@redhat.com>
Reviewed-by: Alex Bligh <a...@alex.org.uk>
---
v4: rebase
v3: rebase
---
include/block/nbd.h | 6 ++++--
nbd/client.c | 8 +++++++-
nbd/server.c | 15 +++++++++++----
3 files changed, 22 insertions(+), 7 deletions(-)
diff --git a/include/block/nbd.h b/include/block/nbd.h
index 7c5103f..6c1d9f4 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -72,11 +72,13 @@ struct nbd_reply {
/* 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. */
diff --git a/nbd/client.c b/nbd/client.c
index 344ebcc..123165b 100644
--- a/nbd/client.c
+++ b/nbd/client.c
@@ -434,6 +434,7 @@ 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>");
@@ -498,6 +499,11 @@ 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)) !=
@@ -585,7 +591,7 @@ 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;
}
diff --git a/nbd/server.c b/nbd/server.c
index ad31c4a..d0ccff0 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -80,6 +80,7 @@ struct NBDClient {
int refcount;
void (*close)(NBDClient *client);
+ bool no_zeroes;
NBDExport *exp;
QCryptoTLSCreds *tlscreds;
char *tlsaclname;
@@ -444,6 +445,11 @@ 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;
@@ -596,6 +602,7 @@ 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")
@@ -612,7 +619,7 @@ 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);
@@ -631,7 +638,7 @@ 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) {
@@ -658,8 +665,8 @@ 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;
}
--
2.5.5
