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Re: [Qemu-block] [PATCH v7 1/9] mirror: inherit supported write/zero fla

From: Eric Blake
Subject: Re: [Qemu-block] [PATCH v7 1/9] mirror: inherit supported write/zero flags
Date: Tue, 30 Jan 2018 10:00:08 -0600
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.5.2

On 01/30/2018 06:15 AM, Anton Nefedov wrote:

>>>> @@ -1064,6 +1064,11 @@ static void
>>>> bdrv_mirror_top_refresh_filename(BlockDriverState *bs, QDict *opts)
>>>>       bdrv_refresh_filename(bs->backing->bs);
>>>>       pstrcpy(bs->exact_filename, sizeof(bs->exact_filename),
>>>>               bs->backing->bs->filename);
>>>> +    bs->supported_write_flags = BDRV_REQ_FUA &
>>>> +        bs->backing->bs->supported_write_flags;

>>> Fundamentally OK, but why is this in *_refresh_filename()?
>> Indeed, I missed that (or maybe it got moved during a botched rebase?).
>> For comparison, blkdebug sets it during blkdebug_open(), and nbd sets it
>> during nbd_client_init() (called during nbd_open()).
> We need a backing bs here and I believe it's not generally set at the
> time of .bdrv_open()

Then is mirror_start_job() a better location, right after we call
bdrv_new_open_driver()?  (Maybe this just goes to show I haven't fully
traced the lifecycle of the mirror driver, and it may all be changing
anyways as we try to fix the BDS graph modifications related with mirrors).

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

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