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| author | Stefan Hajnoczi <stefanha@redhat.com> | 2025-04-17 17:10:53 -0400 |
|---|---|---|
| committer | Kevin Wolf <kwolf@redhat.com> | 2025-05-22 16:54:10 +0200 |
| commit | 5634622bcb339f213469eceeff005640492fc902 (patch) | |
| tree | 7c98c57894653428c5fc72b649f41e64738f8331 | |
| parent | ff2ab634e4bb3bddcf5f5ee29e0b46f71e3f4b54 (diff) | |
| download | qemu-5634622bcb339f213469eceeff005640492fc902.zip qemu-5634622bcb339f213469eceeff005640492fc902.tar.gz qemu-5634622bcb339f213469eceeff005640492fc902.tar.bz2 | |
file-posix: allow BLKZEROOUT with -t writeback
The Linux BLKZEROOUT ioctl is only invoked when BDRV_O_NOCACHE is set
because old kernels did not invalidate the page cache. In that case
mixing BLKZEROOUT with buffered I/O could lead to corruption.
However, Linux 4.9 commit 22dd6d356628 ("block: invalidate the page
cache when issuing BLKZEROOUT") made BLKZEROOUT coherent with the page
cache.
I have checked that Linux 4.9+ kernels are shipped at least as far back
as Debian 10 (buster), openSUSE Leap 15.2, and RHEL/CentOS 8.
Use BLKZEROOUT with buffered I/O, mostly so `qemu-img ... -t
writeback` can offload write zeroes.
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20250417211053.98700-1-stefanha@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
| -rw-r--r-- | block/file-posix.c | 11 |
1 files changed, 0 insertions, 11 deletions
diff --git a/block/file-posix.c b/block/file-posix.c index ec95b74..5a3532e 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -785,17 +785,6 @@ static int raw_open_common(BlockDriverState *bs, QDict *options, } #endif - if (S_ISBLK(st.st_mode)) { -#ifdef __linux__ - /* On Linux 3.10, BLKDISCARD leaves stale data in the page cache. Do - * not rely on the contents of discarded blocks unless using O_DIRECT. - * Same for BLKZEROOUT. - */ - if (!(bs->open_flags & BDRV_O_NOCACHE)) { - s->has_write_zeroes = false; - } -#endif - } #ifdef __FreeBSD__ if (S_ISCHR(st.st_mode)) { /* |