From 5634622bcb339f213469eceeff005640492fc902 Mon Sep 17 00:00:00 2001 From: Stefan Hajnoczi Date: Thu, 17 Apr 2025 17:10:53 -0400 Subject: [PATCH] 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 Cc: Christoph Hellwig Signed-off-by: Stefan Hajnoczi Message-ID: <20250417211053.98700-1-stefanha@redhat.com> Reviewed-by: Eric Blake Reviewed-by: Kevin Wolf Signed-off-by: Kevin Wolf --- block/file-posix.c | 11 ----------- 1 file changed, 11 deletions(-) diff --git a/block/file-posix.c b/block/file-posix.c index ec95b74869..5a3532e40b 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)) { /* -- 2.39.5