[PATCH] block: unmap (discard) blocks only if discard_zeros flag is true

[PATCH] block: unmap (discard) blocks only if discard_zeros flag is true

[luzhipeng]

From: lu zhipeng <luzhipeng@cestc.cn>

we can unmap(discard) blocks for block devices of supporting discard zeros
or regular file.

Signed-off-by: lu zhipeng <luzhipeng@cestc.cn>
---
 block/file-posix.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/block/file-posix.c b/block/file-posix.c
index 48cd096624..c35dbc0d88 100644
--- a/block/file-posix.c
+++ b/block/file-posix.c
@@ -799,7 +799,8 @@ static int raw_open_common(BlockDriverState *bs, QDict *options,
 #endif
     s->needs_alignment = raw_needs_alignment(bs);
 
-    bs->supported_zero_flags = BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK;
+    bs->supported_zero_flags = s->discard_zeroes ?
+                               BDRV_REQ_MAY_UNMAP | BDRV_REQ_NO_FALLBACK : 0;
     if (S_ISREG(st.st_mode)) {
         /* When extending regular files, we get zeros from the OS */
         bs->supported_truncate_flags = BDRV_REQ_ZERO_WRITE;
-- 
2.31.1

Re: [PATCH] block: unmap (discard) blocks only if discard_zeros flag is true

[Kevin Wolf]

Am 23.09.2022 um 12:02 hat luzhipeng geschrieben:
> From: lu zhipeng <luzhipeng@cestc.cn>
> 
> we can unmap(discard) blocks for block devices of supporting discard zeros
> or regular file.
> 
> Signed-off-by: lu zhipeng <luzhipeng@cestc.cn>

This more or less restores the state before commit 34fa110e. The commit
message there explains that s->discard_zeroes is unreliable (in
particular, it is false on block devices on recent kernels even though
they may support zeroing by discard just fine).

We should instead remove s->discard_zeroes because it is currently
unused. I'll send a patch.

Kevin

Re: [PATCH] block: unmap (discard) blocks only if discard_zeros flag is true

[luzhipeng]

在 2022/9/23 22:28, Kevin Wolf 写道:
> Am 23.09.2022 um 12:02 hat luzhipeng geschrieben:
>> From: lu zhipeng <luzhipeng@cestc.cn>
>>
>> we can unmap(discard) blocks for block devices of supporting discard zeros
>> or regular file.
>>
>> Signed-off-by: lu zhipeng <luzhipeng@cestc.cn>
> 
> This more or less restores the state before commit 34fa110e. The commit
> message there explains that s->discard_zeroes is unreliable (in
> particular, it is false on block devices on recent kernels even though
> they may support zeroing by discard just fine).
> 
> We should instead remove s->discard_zeroes because it is currently
> unused. I'll send a patch.
> 
> Kevin
> 
> 
> 
OK