Re: [Qemu-block] [Qemu-devel] [PATCH for-2.10 2/5] block: Allow reopen rw without BDRV_O_ALLOW_RDWR

[Eric Blake]

On 08/03/2017 10:02 AM, Kevin Wolf wrote:
> BDRV_O_ALLOW_RDWR is a flag that tells whether qemu can internally
> reopen a node read-write temporarily because the user requested
> read-write for the top-level image, but qemu decided that read-only is
> enough for this node (a backing file).
> 
> bdrv_reopen() is different, it is also used for cases where the user
> changed their mind and wants to update the options. There is no reason
> to forbid making a node read-write in that case.

Hmm, I wonder.  https://bugzilla.redhat.com/show_bug.cgi?id=1465320
details a failure when starting qemu with a read-write NBD disk, then
taking several snapshots (nbd <- snap1 <- snap2 <- snap3), then where
intermediate commit (snap2 into nbd) works but live commit (snap3 into
nbd) fails with a message that nbd does not support reopening.  I'm
presuming that your series may help to address that; I'll give it a spin
and see what happens.  But first, the code review:

> 
> Signed-off-by: Kevin Wolf <address@hidden>
> ---
>  include/block/block.h |  3 ++-
>  block.c               | 11 +++++++----
>  2 files changed, 9 insertions(+), 5 deletions(-)
> 

Reviewed-by: Eric Blake <address@hidden>

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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