Commit fb1a6de1 authored by Eric Blake's avatar Eric Blake Committed by Stefan Hajnoczi
Browse files

nbd: Rely on block layer to break up large requests 



Now that the block layer will honor max_transfer, we can simplify
our code to rely on that guarantee.

The readv code can call directly into nbd-client, just as the
writev code has done since commit 52a46505.

Interestingly enough, while qemu-io 'w 0 40m' splits into a 32M
and 8M transaction, 'w -z 0 40m' splits into two 16M and an 8M,
because the block layer caps the bounce buffer for writing zeroes
at 16M.  When we later introduce support for NBD_CMD_WRITE_ZEROES,
we can get a full 32M zero write (or larger, if the client and
server negotiate that write zeroes can use a larger size than
ordinary writes).

Signed-off-by: default avatarEric Blake <eblake@redhat.com>
Reviewed-by: default avatarFam Zheng <famz@redhat.com>
Reviewed-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Acked-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Message-id: 1468607524-19021-5-git-send-email-eblake@redhat.com
Signed-off-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent 04ed95f4

block/nbd-client.c

+8 −43
Original line number Diff line number Diff line
@@ -217,15 +217,15 @@ static void nbd_coroutine_end(NbdClientSession *s, 
    }

}



static int nbd_co_readv_1(BlockDriverState *bs, int64_t sector_num,

                          int nb_sectors, QEMUIOVector *qiov,

                          int offset)

int nbd_client_co_readv(BlockDriverState *bs, int64_t sector_num,

                        int nb_sectors, QEMUIOVector *qiov)

{

    NbdClientSession *client = nbd_get_client_session(bs);

    struct nbd_request request = { .type = NBD_CMD_READ };

    struct nbd_reply reply;

    ssize_t ret;



    assert(nb_sectors <= NBD_MAX_SECTORS);

    request.from = sector_num * 512;

    request.len = nb_sectors * 512;
@@ -234,16 +234,15 @@ static int nbd_co_readv_1(BlockDriverState *bs, int64_t sector_num, 
    if (ret < 0) {

        reply.error = -ret;

    } else {

        nbd_co_receive_reply(client, &request, &reply, qiov, offset);

        nbd_co_receive_reply(client, &request, &reply, qiov, 0);

    }

    nbd_coroutine_end(client, &request);

    return -reply.error;



}



static int nbd_co_writev_1(BlockDriverState *bs, int64_t sector_num,

                           int nb_sectors, QEMUIOVector *qiov,

                           int offset, int flags)

int nbd_client_co_writev(BlockDriverState *bs, int64_t sector_num,

                         int nb_sectors, QEMUIOVector *qiov, int flags)

{

    NbdClientSession *client = nbd_get_client_session(bs);

    struct nbd_request request = { .type = NBD_CMD_WRITE };
@@ -255,11 +254,12 @@ static int nbd_co_writev_1(BlockDriverState *bs, int64_t sector_num, 
        request.type |= NBD_CMD_FLAG_FUA;

    }



    assert(nb_sectors <= NBD_MAX_SECTORS);

    request.from = sector_num * 512;

    request.len = nb_sectors * 512;



    nbd_coroutine_start(client, &request);

    ret = nbd_co_send_request(bs, &request, qiov, offset);

    ret = nbd_co_send_request(bs, &request, qiov, 0);

    if (ret < 0) {

        reply.error = -ret;

    } else {
@@ -269,41 +269,6 @@ static int nbd_co_writev_1(BlockDriverState *bs, int64_t sector_num, 
    return -reply.error;

}



int nbd_client_co_readv(BlockDriverState *bs, int64_t sector_num,

                        int nb_sectors, QEMUIOVector *qiov)

{

    int offset = 0;

    int ret;

    while (nb_sectors > NBD_MAX_SECTORS) {

        ret = nbd_co_readv_1(bs, sector_num, NBD_MAX_SECTORS, qiov, offset);

        if (ret < 0) {

            return ret;

        }

        offset += NBD_MAX_SECTORS * 512;

        sector_num += NBD_MAX_SECTORS;

        nb_sectors -= NBD_MAX_SECTORS;

    }

    return nbd_co_readv_1(bs, sector_num, nb_sectors, qiov, offset);

}



int nbd_client_co_writev(BlockDriverState *bs, int64_t sector_num,

                         int nb_sectors, QEMUIOVector *qiov, int flags)

{

    int offset = 0;

    int ret;

    while (nb_sectors > NBD_MAX_SECTORS) {

        ret = nbd_co_writev_1(bs, sector_num, NBD_MAX_SECTORS, qiov, offset,

                              flags);

        if (ret < 0) {

            return ret;

        }

        offset += NBD_MAX_SECTORS * 512;

        sector_num += NBD_MAX_SECTORS;

        nb_sectors -= NBD_MAX_SECTORS;

    }

    return nbd_co_writev_1(bs, sector_num, nb_sectors, qiov, offset, flags);

}



int nbd_client_co_flush(BlockDriverState *bs)

{

    NbdClientSession *client = nbd_get_client_session(bs);

block/nbd.c

+3 −9
Original line number Diff line number Diff line
@@ -349,12 +349,6 @@ static int nbd_open(BlockDriverState *bs, QDict *options, int flags, 
    return ret;

}



static int nbd_co_readv(BlockDriverState *bs, int64_t sector_num,

                        int nb_sectors, QEMUIOVector *qiov)

{

    return nbd_client_co_readv(bs, sector_num, nb_sectors, qiov);

}



static int nbd_co_flush(BlockDriverState *bs)

{

    return nbd_client_co_flush(bs);
@@ -450,7 +444,7 @@ static BlockDriver bdrv_nbd = { 
    .instance_size              = sizeof(BDRVNBDState),

    .bdrv_parse_filename        = nbd_parse_filename,

    .bdrv_file_open             = nbd_open,

    .bdrv_co_readv              = nbd_co_readv,

    .bdrv_co_readv              = nbd_client_co_readv,

    .bdrv_co_writev_flags       = nbd_client_co_writev,

    .bdrv_close                 = nbd_close,

    .bdrv_co_flush_to_os        = nbd_co_flush,
@@ -468,7 +462,7 @@ static BlockDriver bdrv_nbd_tcp = { 
    .instance_size              = sizeof(BDRVNBDState),

    .bdrv_parse_filename        = nbd_parse_filename,

    .bdrv_file_open             = nbd_open,

    .bdrv_co_readv              = nbd_co_readv,

    .bdrv_co_readv              = nbd_client_co_readv,

    .bdrv_co_writev_flags       = nbd_client_co_writev,

    .bdrv_close                 = nbd_close,

    .bdrv_co_flush_to_os        = nbd_co_flush,
@@ -486,7 +480,7 @@ static BlockDriver bdrv_nbd_unix = { 
    .instance_size              = sizeof(BDRVNBDState),

    .bdrv_parse_filename        = nbd_parse_filename,

    .bdrv_file_open             = nbd_open,

    .bdrv_co_readv              = nbd_co_readv,

    .bdrv_co_readv              = nbd_client_co_readv,

    .bdrv_co_writev_flags       = nbd_client_co_writev,

    .bdrv_close                 = nbd_close,

    .bdrv_co_flush_to_os        = nbd_co_flush,