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> --- 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 155196e..35c0ea3 100644 --- a/include/block/nbd.h +++ b/include/block/nbd.h @@ -73,11 +73,13 @@ typedef struct nbd_reply 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 d4e37d5..507ddc1 100644 --- a/nbd/client.c +++ b/nbd/client.c @@ -409,6 +409,7 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, uint32_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>"); @@ -475,6 +476,11 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, uint32_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)) != @@ -558,7 +564,7 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, uint32_t *flags, goto fail; } - 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 69724c9..379df8c 100644 --- a/nbd/server.c +++ b/nbd/server.c @@ -78,6 +78,7 @@ struct NBDClient { int refcount; void (*close)(NBDClient *client); + bool no_zeroes; NBDExport *exp; QCryptoTLSCreds *tlscreds; char *tlsaclname; @@ -396,6 +397,11 @@ 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; @@ -527,6 +533,7 @@ 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") @@ -543,7 +550,7 @@ 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); @@ -560,7 +567,7 @@ 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) { @@ -585,8 +592,8 @@ static coroutine_fn int nbd_negotiate(NBDClientNewData *data) 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