[Qemu-block] [PULL v2 9/9] nbd: Implement server use of NBD FAST_ZERO

[Eric Blake]

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 <ebl...@redhat.com>
Message-Id: <20190823143726.27062-5-ebl...@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com>
[eblake: update iotests 223, 233]
---
 nbd/server.c               | 8 ++++++--
 tests/qemu-iotests/223.out | 2 +-
 tests/qemu-iotests/233.out | 2 +-
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/nbd/server.c b/nbd/server.c
index 4992148de1c4..28c3c8be854c 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -1513,7 +1513,8 @@ 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);
@@ -2166,7 +2167,7 @@ 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;
     }
@@ -2305,6 +2306,9 @@ 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,
diff --git a/tests/qemu-iotests/223.out b/tests/qemu-iotests/223.out
index 2db0dc991a27..5d00398c11cb 100644
--- a/tests/qemu-iotests/223.out
+++ b/tests/qemu-iotests/223.out
@@ -49,7 +49,7 @@ exports available: 2
    qemu:dirty-bitmap:b
  export: 'n2'
   size:  4194304
-  flags: 0x4ed ( flush fua trim zeroes df cache )
+  flags: 0xced ( flush fua trim zeroes df cache fast-zero )
   min block: 1
   opt block: 4096
   max block: 33554432
diff --git a/tests/qemu-iotests/233.out b/tests/qemu-iotests/233.out
index a3ecc4eb5ccf..24321efa113b 100644
--- a/tests/qemu-iotests/233.out
+++ b/tests/qemu-iotests/233.out
@@ -37,7 +37,7 @@ disk size: unavailable
 exports available: 1
  export: ''
   size:  67108864
-  flags: 0x4ed ( flush fua trim zeroes df cache )
+  flags: 0xced ( flush fua trim zeroes df cache fast-zero )
   min block: 1
   opt block: 4096
   max block: 33554432
-- 
2.21.0