qemu /
qemu /
5634622bcb339f213469eceeff005640492fc902 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>
1 file changed
