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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 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
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51
block/nbd-client.c
View File

@ -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);

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,