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nbd: Rely on block layer to break up large requests

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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 52a4650.

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: Eric Blake <eblake@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1468607524-19021-5-git-send-email-eblake@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
Eric Blake 2016-07-15 12:32:02 -06:00 • committed by Stefan Hajnoczi
parent 04ed95f484
commit fb1a6de14a
2 changed files with 11 additions and 52 deletions
Download patch file Download diff file Expand all files Collapse all files

12
block/nbd.c
View file

@ -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,