Commit c203c59a authored by Eric Blake's avatar Eric Blake Committed by Paolo Bonzini
Browse files

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: default avatarEric Blake <eblake@redhat.com>
Reviewed-by: default avatarAlex Bligh <alex@alex.org.uk>
Message-Id: <1476469998-28592-13-git-send-email-eblake@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 75368aab

include/block/nbd.h

+4 −2
Original line number Diff line number Diff line
@@ -75,10 +75,12 @@ 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_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_NO_ZEROES      (1 << 1) /* End handshake without zeroes. */



/* Reply types. */

#define NBD_REP_ACK             (1)             /* Data sending finished. */

nbd/client.c

+7 −1
Original line number Diff line number Diff line
@@ -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;

    }

nbd/server.c

+11 −4
Original line number Diff line number Diff line
@@ -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;

        }