Patchwork [22/23] block: Always enable discard on the protocol level

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Submitter Stefan Hajnoczi
Date June 24, 2013, 9:10 a.m.
Message ID <>
Download mbox | patch
Permalink /patch/253766/
State New
Headers show


Stefan Hajnoczi - June 24, 2013, 9:10 a.m.
From: Kevin Wolf <>

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

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 <>
Signed-off-by: Stefan Hajnoczi <>
 block.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)


diff --git a/block.c b/block.c
index b88ad2f..8e77d46 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;