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c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1744924260; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=7pqbBncs4V+SEDkICJlqa8chCxJKrfcfYWPXIcEE80A=; b=FhqOBM5CWwzykoTR+afGcH4bGRfyhs0I9AV77z/RELid7y+0CiXUzREzqehnHHbQqHflnt aCXuomwnFP0dHs1/dJbcPyFJfmv5+rovz9pCZ75tgXzjdW0IkP2s9+F2mMCxOwvNCkIoBl qurxREJd8SPKeNzt9WuNGcz4Bs7Y83M= X-MC-Unique: JzLR8leJO1GIfsAg5Gcygg-1 X-Mimecast-MFC-AGG-ID: JzLR8leJO1GIfsAg5Gcygg_1744924255 From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: qemu-block@nongnu.org, Hanna Reitz , Kevin Wolf , Stefan Hajnoczi , Paolo Bonzini , Christoph Hellwig Subject: [PATCH] block/file-posix: allow BLKZEROOUT with -t writeback Date: Thu, 17 Apr 2025 17:10:53 -0400 Message-ID: <20250417211053.98700-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; 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charset="utf-8" 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 Reviewed-by: Eric Blake --- block/file-posix.c | 11 ----------- 1 file changed, 11 deletions(-) diff --git a/block/file-posix.c b/block/file-posix.c index 56d1972d15..9ba0b68958 100644 --- a/block/file-posix.c +++ b/block/file-posix.c @@ -781,17 +781,6 @@ static int raw_open_common(BlockDriverState *bs, QDict= *options, } #endif =20 - 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_DIR= ECT. - * Same for BLKZEROOUT. - */ - if (!(bs->open_flags & BDRV_O_NOCACHE)) { - s->has_write_zeroes =3D false; - } -#endif - } #ifdef __FreeBSD__ if (S_ISCHR(st.st_mode)) { /* --=20 2.49.0