On 8 Apr 2016, at 23:05, Eric Blake <ebl...@redhat.com> wrote: > 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 */
Surely you only need to do this is the flag wasn't sent to the server, i.e. if !(client->nbdflags & NBD_FLAG_SEND_FUA) If you've sent a FUA request, no need to flush the whole thing. nbd_co_writev_flags seems to have the same issue, which is where I guess you got that from. > + 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 > > -- Alex Bligh