[Qemu-devel] [PATCH 5/5] block: Always enable discard on the protocol level

[Kevin Wolf <kwolf@redhat.com>]

Turning on discard options in qcow2 doesn't help a lot when the discard
requests that it issues are thrown away by the raw-posix layer. This
patch always enables discard functionality on the protocol level so that
it's the image format's responsibility to send (or not) discard
requests. Requests sent by the guest will be allowed or ignored by the
top level BlockDriverState, which depends on the discard=... option like
before.

In particular, this means that even without specifying options, the
qcow2 default of discarding deleted snapshots actually takes effect now,
both for qemu and qemu-img.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 block.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/block.c b/block.c
index 79ad33d..0a7cf2f 100644
--- a/block.c
+++ b/block.c
@@ -1045,7 +1045,7 @@ int bdrv_open(BlockDriverState *bs, const char *filename, QDict *options,
     extract_subqdict(options, &file_options, "file.");
 
     ret = bdrv_file_open(&file, filename, file_options,
-                         bdrv_open_flags(bs, flags));
+                         bdrv_open_flags(bs, flags | BDRV_O_UNMAP));
     if (ret < 0) {
         goto fail;
     }
-- 
1.8.1.4