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From ab2ef6c7b0c99840a5b530899076998a7bbdf5df Mon Sep 17 00:00:00 2001
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From: Kevin Wolf <kwolf@redhat.com>
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Date: Mon, 15 Jan 2018 11:23:35 +0100
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Subject: [PATCH 10/12] block: Don't use BLK_PERM_CONSISTENT_READ for format
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probing
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RH-Author: Kevin Wolf <kwolf@redhat.com>
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Message-id: <20180115112337.20885-2-kwolf@redhat.com>
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Patchwork-id: 78573
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O-Subject: [RHV-7.5 qemu-kvm-rhev PATCH 1/3] block: Don't use BLK_PERM_CONSISTENT_READ for format probing
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Bugzilla: 1515604
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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RH-Acked-by: Jeffrey Cody <jcody@redhat.com>
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RH-Acked-by: John Snow <jsnow@redhat.com>
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For format probing, we don't really care whether all of the image
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content is consistent. The only thing we're looking at is the image
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header, and specifically the magic numbers that are expected to never
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change, no matter how inconsistent the guest visible disk content is.
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Therefore, don't request BLK_PERM_CONSISTENT_READ. This allows to use
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format probing, e.g. in the context of 'qemu-img info', even while the
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guest visible data in the image is inconsistent during a running block
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job.
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Reviewed-by: Fam Zheng <famz@redhat.com>
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(cherry picked from commit dacaa16238cc5915a609ddaab4b7f81c4bceb9ae)
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Signed-off-by: Kevin Wolf <kwolf@redhat.com>
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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block.c | 5 ++++-
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1 file changed, 4 insertions(+), 1 deletion(-)
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diff --git a/block.c b/block.c
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index 17629ab..90a60bc 100644
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--- a/block.c
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+++ b/block.c
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@@ -2540,7 +2540,10 @@ static BlockDriverState *bdrv_open_inherit(const char *filename,
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goto fail;
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}
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if (file_bs != NULL) {
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- file = blk_new(BLK_PERM_CONSISTENT_READ, BLK_PERM_ALL);
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+ /* Not requesting BLK_PERM_CONSISTENT_READ because we're only
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+ * looking at the header to guess the image format. This works even
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+ * in cases where a guest would not see a consistent state. */
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+ file = blk_new(0, BLK_PERM_ALL);
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blk_insert_bs(file, file_bs, &local_err);
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bdrv_unref(file_bs);
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if (local_err) {
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--
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1.8.3.1
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