mbox series

[0/2] block: Fix qemu-img creating overlay when guest running

Message ID 20171215080446.10671-1-famz@redhat.com
Headers show
Series block: Fix qemu-img creating overlay when guest running | expand

Message

Fam Zheng Dec. 15, 2017, 8:04 a.m. UTC 
Shared write lock is not strictly necessary for creating the overlay image, if
all what we want is to probe the size.

Fam Zheng (2):
  block: Open backing image in force share mode for size probe
  iotests: Test creating overlay when guest running

 block.c                    | 3 ++-
 tests/qemu-iotests/153     | 4 ++++
 tests/qemu-iotests/153.out | 3 +++
 3 files changed, 9 insertions(+), 1 deletion(-)

Comments

Eric Blake Dec. 15, 2017, 7:51 p.m. UTC | #1 
On 12/15/2017 02:04 AM, Fam Zheng wrote:
> Shared write lock is not strictly necessary for creating the overlay image, if
> all what we want is to probe the size.

Theoretically, the size could be changing due to a resize operation.
But realistically, even if that happens, we will (hopefully) see either
the old size or the new size atomically (that is, I seriously doubt the
size information is split across multiple sectors of the in-use image to
the point that we could shard the read).

Series:
Reviewed-by: Eric Blake <eblake@redhat.com>