[Libguestfs] [PATCH 4/5] nbd: Implement server use of NBD FAST_ZERO

The server side is fairly straightforward: we can always advertise support for detection of fast zero, and implement it by mapping the request to the block layer BDRV_REQ_NO_FALLBACK. Signed-off-by: Eric Blake <eblake(a)redhat.com&gt; --- Again, this may be worth merging with the previous patch. --- nbd/server.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/nbd/server.c b/nbd/server.c index 981bc3cb1151..3c0799eda87f 100644 --- a/nbd/server.c +++ b/nbd/server.c @@ -1514,7 +1514,8 @@ NBDExport *nbd_export_new(BlockDriverState *bs, uint64_t dev_offset, exp->nbdflags |= NBD_FLAG_CAN_MULTI_CONN; } } else { - exp->nbdflags |= NBD_FLAG_SEND_TRIM | NBD_FLAG_SEND_WRITE_ZEROES; + exp->nbdflags |= (NBD_FLAG_SEND_TRIM | NBD_FLAG_SEND_WRITE_ZEROES | + NBD_FLAG_SEND_FAST_ZERO); } assert(size <= INT64_MAX - dev_offset); exp->size = QEMU_ALIGN_DOWN(size, BDRV_SECTOR_SIZE); @@ -2167,7 +2168,7 @@ static int nbd_co_receive_request(NBDRequestData *req, NBDRequest *request, if (request->type == NBD_CMD_READ && client->structured_reply) { valid_flags |= NBD_CMD_FLAG_DF; } else if (request->type == NBD_CMD_WRITE_ZEROES) { - valid_flags |= NBD_CMD_FLAG_NO_HOLE; + valid_flags |= NBD_CMD_FLAG_NO_HOLE | NBD_CMD_FLAG_FAST_ZERO; } else if (request->type == NBD_CMD_BLOCK_STATUS) { valid_flags |= NBD_CMD_FLAG_REQ_ONE; } @@ -2306,6 +2307,9 @@ static coroutine_fn int nbd_handle_request(NBDClient *client, if (!(request->flags & NBD_CMD_FLAG_NO_HOLE)) { flags |= BDRV_REQ_MAY_UNMAP; } + if (request->flags & NBD_CMD_FLAG_FAST_ZERO) { + flags |= BDRV_REQ_NO_FALLBACK; + } ret = blk_pwrite_zeroes(exp->blk, request->from + exp->dev_offset, request->len, flags); return nbd_send_generic_reply(client, request->handle, ret, -- 2.21.0