RFC because there is still discussion on the NBD list about
adding an NBD_OPT_ to let the client suggest server defaults
related to scanning for zeroes during NBD_CMD_WRITE, which may
tweak this patch.
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 lots of zeroes if we return -ENOTSUP because the server
does not have WRITE_ZEROES.
Signed-off-by: Eric Blake <ebl...@redhat.com>
---
block/nbd-client.h | 2 ++
block/nbd-client.c | 34 ++++++++++++++++++++++++++++++++++
block/nbd.c | 23 +++++++++++++++++++++++
3 files changed, 59 insertions(+)
diff --git a/block/nbd-client.h b/block/nbd-client.h
index bc7aec0..2fe6654 100644
--- a/block/nbd-client.h
+++ b/block/nbd-client.h
@@ -47,6 +47,8 @@ void nbd_client_close(BlockDriverState *bs);
int nbd_client_co_discard(BlockDriverState *bs, int64_t sector_num,
int nb_sectors);
int nbd_client_co_flush(BlockDriverState *bs);
+int nbd_client_co_write_zeroes(BlockDriverState *bs, int64_t sector_num,
+ int nb_sectors, int *flags);
int nbd_client_co_writev(BlockDriverState *bs, int64_t sector_num,
int nb_sectors, QEMUIOVector *qiov, int *flags);
int nbd_client_co_readv(BlockDriverState *bs, int64_t sector_num,
diff --git a/block/nbd-client.c b/block/nbd-client.c
index f013084..4be83a8 100644
--- a/block/nbd-client.c
+++ b/block/nbd-client.c
@@ -291,6 +291,40 @@ int nbd_client_co_readv(BlockDriverState *bs, int64_t
sector_num,
return nbd_co_readv_1(bs, sector_num, nb_sectors, qiov, offset);
}
+int nbd_client_co_write_zeroes(BlockDriverState *bs, int64_t sector_num,
+ int nb_sectors, int *flags)
+{
+ ssize_t ret;
+ NbdClientSession *client = nbd_get_client_session(bs);
+ struct nbd_request request = { .type = NBD_CMD_WRITE_ZEROES };
+ struct nbd_reply reply;
+
+ if (!(client->nbdflags & NBD_FLAG_SEND_WRITE_ZEROES)) {
+ return -ENOTSUP;
+ }
+
+ if ((*flags & BDRV_REQ_FUA) && (client->nbdflags & NBD_FLAG_SEND_FUA)) {
+ *flags &= ~BDRV_REQ_FUA;
+ request.flags |= NBD_CMD_FLAG_FUA;
+ }
+ if (!(*flags & BDRV_REQ_MAY_UNMAP)) {
+ request.flags |= NBD_CMD_FLAG_NO_HOLE;
+ }
+
+ request.from = sector_num * 512;
+ request.len = nb_sectors * 512;
+
+ nbd_coroutine_start(client, &request);
+ ret = nbd_co_send_request(bs, &request, NULL, 0);
+ if (ret < 0) {
+ reply.error = -ret;
+ } else {
+ nbd_co_receive_reply(client, &request, &reply, NULL, 0);
+ }
+ nbd_coroutine_end(client, &request);
+ return -reply.error;
+}
+
int nbd_client_co_writev(BlockDriverState *bs, int64_t sector_num,
int nb_sectors, QEMUIOVector *qiov, int *flags)
{
diff --git a/block/nbd.c b/block/nbd.c
index f7ea3b3..f5119c0 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -355,6 +355,26 @@ static int nbd_co_readv(BlockDriverState *bs, int64_t
sector_num,
return nbd_client_co_readv(bs, sector_num, nb_sectors, qiov);
}
+static int nbd_co_write_zeroes(BlockDriverState *bs, int64_t sector_num,
+ int nb_sectors, BdrvRequestFlags orig_flags)
+{
+ int flags = orig_flags;
+ int ret;
+
+ ret = nbd_client_co_write_zeroes(bs, sector_num, nb_sectors, &flags);
+ if (ret < 0) {
+ return ret;
+ }
+
+ /* The flag wasn't sent to the server, so we need to emulate it with an
+ * explicit flush */
+ if (flags & BDRV_REQ_FUA) {
+ ret = nbd_client_co_flush(bs);
+ }
+
+ return ret;
+}
+
static int nbd_co_writev_flags(BlockDriverState *bs, int64_t sector_num,
int nb_sectors, QEMUIOVector *qiov, int flags)
{
@@ -476,6 +496,7 @@ static BlockDriver bdrv_nbd = {
.bdrv_parse_filename = nbd_parse_filename,
.bdrv_file_open = nbd_open,
.bdrv_co_readv = nbd_co_readv,
+ .bdrv_co_write_zeroes = nbd_co_write_zeroes,
.bdrv_co_writev = nbd_co_writev,
.bdrv_co_writev_flags = nbd_co_writev_flags,
.supported_write_flags = BDRV_REQ_FUA,
@@ -496,6 +517,7 @@ static BlockDriver bdrv_nbd_tcp = {
.bdrv_parse_filename = nbd_parse_filename,
.bdrv_file_open = nbd_open,
.bdrv_co_readv = nbd_co_readv,
+ .bdrv_co_write_zeroes = nbd_co_write_zeroes,
.bdrv_co_writev = nbd_co_writev,
.bdrv_co_writev_flags = nbd_co_writev_flags,
.supported_write_flags = BDRV_REQ_FUA,
@@ -516,6 +538,7 @@ static BlockDriver bdrv_nbd_unix = {
.bdrv_parse_filename = nbd_parse_filename,
.bdrv_file_open = nbd_open,
.bdrv_co_readv = nbd_co_readv,
+ .bdrv_co_write_zeroes = nbd_co_write_zeroes,
.bdrv_co_writev = nbd_co_writev,
.bdrv_co_writev_flags = nbd_co_writev_flags,
.supported_write_flags = BDRV_REQ_FUA,
--
2.5.5
