[Qemu-devel] [PATCH 20/25] block/nbd: Comment on discard/flush silently failing

[Max Reitz <mreitz@redhat.com>]

If some operation cannot be performed by a block driver, it is normally
supposed to return an error. In these cases, however, it is fine to
pretend the operations were carried out successfully because if the NBD
block driver would not implement discard or flush in the first place,
this is exactly what the block layer would do.

Because this may not be obvious, add a comment for it.

Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/nbd-client.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/block/nbd-client.c b/block/nbd-client.c
index be6803d..ab13607 100644
--- a/block/nbd-client.c
+++ b/block/nbd-client.c
@@ -315,6 +315,7 @@ int nbd_client_co_flush(BlockDriverState *bs)
     ssize_t ret;
 
     if (!(client->nbdflags & NBD_FLAG_SEND_FLUSH)) {
+        /* This mirrors the behavior of bdrv_co_flush() in block.c */
         return 0;
     }
 
@@ -350,6 +351,7 @@ int nbd_client_co_discard(BlockDriverState *bs, int64_t sector_num,
     ssize_t ret;
 
     if (!(client->nbdflags & NBD_FLAG_SEND_TRIM)) {
+        /* This mirrors the behavior of bdrv_co_discard() in block.c */
         return 0;
     }
     request.from = sector_num * 512;
-- 
2.1.0