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c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1759846648; 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: in-reply-to:in-reply-to:references:references; bh=ENlFcRQgNbls4QxNgPIhoAoPPfSEdRpUnvkCRsps668=; b=Ba+JCI3esRw3FJhwpBgt/RBshXYsfPE2oFIlIUavtW+5daZ0urYIgvjKJSQ6h3GPmx+ShE YVvX9sLk85F+rnbRWe8ul8wrYW+QsZA+01tbre0hS3yJ4W+kCyXcFf5Q2i9hfGqNj+zM3Z mun9Tom7BoEqEXGQnf6tFcPQ5TaLzhE= X-MC-Unique: CtRjM73NM02AIF3eIcpRtw-1 X-Mimecast-MFC-AGG-ID: CtRjM73NM02AIF3eIcpRtw_1759846637 From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: qemu-block@nongnu.org, Kevin Wolf , Jean-Louis Dupond , Vladimir Sementsov-Ogievskiy , Hanna Reitz , Stefan Hajnoczi Subject: [PATCH v2 2/3] block: use pwrite_zeroes_alignment when writing first sector Date: Tue, 7 Oct 2025 10:16:59 -0400 Message-ID: <20251007141700.71891-3-stefanha@redhat.com> In-Reply-To: <20251007141700.71891-1-stefanha@redhat.com> References: <20251007141700.71891-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 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" Since commit 5634622bcb33 ("file-posix: allow BLKZEROOUT with -t writeback"), qemu-img create errors out on a Linux loop block device with a 4 KB sector size: # dd if=3D/dev/zero of=3Dblockfile bs=3D1M count=3D1024 # losetup --sector-size 4096 /dev/loop0 blockfile # qemu-img create -f raw /dev/loop0 1G Formatting '/dev/loop0', fmt=3Draw size=3D1073741824 qemu-img: /dev/loop0: Failed to clear the new image's first sector: Inval= id argument Use the pwrite_zeroes_alignment block limit to avoid misaligned fallocate(2) or ioctl(BLKZEROOUT) in the block/file-posix.c block driver. Fixes: 5634622bcb33 ("file-posix: allow BLKZEROOUT with -t writeback") Reported-by: Jean-Louis Dupond Buglink: https://gitlab.com/qemu-project/qemu/-/issues/3127 Reviewed-by: Vladimir Sementsov-Ogievskiy Signed-off-by: Stefan Hajnoczi --- include/system/block-backend-io.h | 1 + block.c | 3 ++- block/block-backend.c | 11 +++++++++++ 3 files changed, 14 insertions(+), 1 deletion(-) diff --git a/include/system/block-backend-io.h b/include/system/block-backe= nd-io.h index ba8dfcc7d0..6d5ac476fc 100644 --- a/include/system/block-backend-io.h +++ b/include/system/block-backend-io.h @@ -116,6 +116,7 @@ BlockAIOCB *blk_abort_aio_request(BlockBackend *blk, void *opaque, int ret); =20 uint32_t blk_get_request_alignment(BlockBackend *blk); +uint32_t blk_get_pwrite_zeroes_alignment(BlockBackend *blk); uint32_t blk_get_max_transfer(BlockBackend *blk); uint64_t blk_get_max_hw_transfer(BlockBackend *blk); =20 diff --git a/block.c b/block.c index 8848e9a7ed..be77e03904 100644 --- a/block.c +++ b/block.c @@ -606,12 +606,13 @@ create_file_fallback_zero_first_sector(BlockBackend *= blk, int64_t current_size, Error **errp) { + uint32_t alignment =3D blk_get_pwrite_zeroes_alignment(blk); int64_t bytes_to_clear; int ret; =20 GLOBAL_STATE_CODE(); =20 - bytes_to_clear =3D MIN(current_size, BDRV_SECTOR_SIZE); + bytes_to_clear =3D MIN(current_size, MAX(BDRV_SECTOR_SIZE, alignment)); if (bytes_to_clear) { ret =3D blk_co_pwrite_zeroes(blk, 0, bytes_to_clear, BDRV_REQ_MAY_= UNMAP); if (ret < 0) { diff --git a/block/block-backend.c b/block/block-backend.c index f8d6ba65c1..239d6eca37 100644 --- a/block/block-backend.c +++ b/block/block-backend.c @@ -2305,6 +2305,17 @@ uint32_t blk_get_request_alignment(BlockBackend *blk) return bs ? bs->bl.request_alignment : BDRV_SECTOR_SIZE; } =20 +/* Returns the optimal write zeroes alignment, in bytes; guaranteed nonzer= o */ +uint32_t blk_get_pwrite_zeroes_alignment(BlockBackend *blk) +{ + BlockDriverState *bs =3D blk_bs(blk); + IO_CODE(); + if (!bs) { + return BDRV_SECTOR_SIZE; + } + return bs->bl.pwrite_zeroes_alignment ?: bs->bl.request_alignment; +} + /* Returns the maximum hardware transfer length, in bytes; guaranteed nonz= ero */ uint64_t blk_get_max_hw_transfer(BlockBackend *blk) { --=20 2.51.0