On 2015-03-11 at 07:31, Paolo Bonzini wrote:
On 25/02/2015 19:08, Max Reitz wrote: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 <mre...@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;Should this return -EOPNOTSUPP instead?
That's what this patch is for. I asked myself the same thing, and it turns out, the functions deliberately return 0 because bdrv_co_flush() and bdrv_co_discard() do the same if the block driver does not support these functions at all, so that's why I'm adding these comments.
Max
Paolo} request.from = sector_num * 512;
