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