Commit fa778fff authored by Eric Blake's avatar Eric Blake Committed by Paolo Bonzini
Browse files

nbd: Implement NBD_CMD_WRITE_ZEROES on client 

Upstream NBD protocol recently added the ability to efficiently
write zeroes without having to send the zeroes over the wire,
along with a flag to control whether the client wants a hole.

The generic block code takes care of falling back to the obvious
write of lots of zeroes if we return -ENOTSUP because the server
does not have WRITE_ZEROES.

Ideally, since NBD_CMD_WRITE_ZEROES does not involve any data
over the wire, we want to support transactions that are much
larger than the normal 32M limit imposed on NBD_CMD_WRITE.  But
the server may still have a limit smaller than UINT_MAX, so
until experimental NBD protocol additions for advertising various
command sizes is finalized (see [1], [2]), for now we just stick to
the same limits as normal writes.

[1] https://github.com/yoe/nbd/blob/extension-info/doc/proto.md
[2] https://sourceforge.net/p/nbd/mailman/message/35081223/



Signed-off-by: default avatarEric Blake <eblake@redhat.com>
Message-Id: <1476469998-28592-17-git-send-email-eblake@redhat.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 1f4d6d18

block/nbd-client.c

+35 −0
Original line number Diff line number Diff line
@@ -275,6 +275,41 @@ int nbd_client_co_pwritev(BlockDriverState *bs, uint64_t offset, 
    return -reply.error;

}



int nbd_client_co_pwrite_zeroes(BlockDriverState *bs, int64_t offset,

                                int count, BdrvRequestFlags flags)

{

    ssize_t ret;

    NBDClientSession *client = nbd_get_client_session(bs);

    NBDRequest request = {

        .type = NBD_CMD_WRITE_ZEROES,

        .from = offset,

        .len = count,

    };

    NBDReply reply;



    if (!(client->nbdflags & NBD_FLAG_SEND_WRITE_ZEROES)) {

        return -ENOTSUP;

    }



    if (flags & BDRV_REQ_FUA) {

        assert(client->nbdflags & NBD_FLAG_SEND_FUA);

        request.flags |= NBD_CMD_FLAG_FUA;

    }

    if (!(flags & BDRV_REQ_MAY_UNMAP)) {

        request.flags |= NBD_CMD_FLAG_NO_HOLE;

    }



    nbd_coroutine_start(client, &request);

    ret = nbd_co_send_request(bs, &request, NULL);

    if (ret < 0) {

        reply.error = -ret;

    } else {

        nbd_co_receive_reply(client, &request, &reply, NULL);

    }

    nbd_coroutine_end(client, &request);

    return -reply.error;

}



int nbd_client_co_flush(BlockDriverState *bs)

{

    NBDClientSession *client = nbd_get_client_session(bs);

block/nbd-client.h

+2 −0
Original line number Diff line number Diff line
@@ -48,6 +48,8 @@ int nbd_client_co_pdiscard(BlockDriverState *bs, int64_t offset, int count); 
int nbd_client_co_flush(BlockDriverState *bs);

int nbd_client_co_pwritev(BlockDriverState *bs, uint64_t offset,

                          uint64_t bytes, QEMUIOVector *qiov, int flags);

int nbd_client_co_pwrite_zeroes(BlockDriverState *bs, int64_t offset,

                                int count, BdrvRequestFlags flags);

int nbd_client_co_preadv(BlockDriverState *bs, uint64_t offset,

                         uint64_t bytes, QEMUIOVector *qiov, int flags);

block/nbd.c

+4 −0
Original line number Diff line number Diff line
@@ -466,6 +466,7 @@ static int nbd_co_flush(BlockDriverState *bs) 
static void nbd_refresh_limits(BlockDriverState *bs, Error **errp)

{

    bs->bl.max_pdiscard = NBD_MAX_BUFFER_SIZE;

    bs->bl.max_pwrite_zeroes = NBD_MAX_BUFFER_SIZE;

    bs->bl.max_transfer = NBD_MAX_BUFFER_SIZE;

}
@@ -558,6 +559,7 @@ static BlockDriver bdrv_nbd = { 
    .bdrv_file_open             = nbd_open,

    .bdrv_co_preadv             = nbd_client_co_preadv,

    .bdrv_co_pwritev            = nbd_client_co_pwritev,

    .bdrv_co_pwrite_zeroes      = nbd_client_co_pwrite_zeroes,

    .bdrv_close                 = nbd_close,

    .bdrv_co_flush_to_os        = nbd_co_flush,

    .bdrv_co_pdiscard           = nbd_client_co_pdiscard,
@@ -576,6 +578,7 @@ static BlockDriver bdrv_nbd_tcp = { 
    .bdrv_file_open             = nbd_open,

    .bdrv_co_preadv             = nbd_client_co_preadv,

    .bdrv_co_pwritev            = nbd_client_co_pwritev,

    .bdrv_co_pwrite_zeroes      = nbd_client_co_pwrite_zeroes,

    .bdrv_close                 = nbd_close,

    .bdrv_co_flush_to_os        = nbd_co_flush,

    .bdrv_co_pdiscard           = nbd_client_co_pdiscard,
@@ -594,6 +597,7 @@ static BlockDriver bdrv_nbd_unix = { 
    .bdrv_file_open             = nbd_open,

    .bdrv_co_preadv             = nbd_client_co_preadv,

    .bdrv_co_pwritev            = nbd_client_co_pwritev,

    .bdrv_co_pwrite_zeroes      = nbd_client_co_pwrite_zeroes,

    .bdrv_close                 = nbd_close,

    .bdrv_co_flush_to_os        = nbd_co_flush,

    .bdrv_co_pdiscard           = nbd_client_co_pdiscard,