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From: Eric Blake <eblake@redhat.com>
Message-ID: <c06a66f0-5883-613d-59c0-160b0fd27925@redhat.com>
Date: Tue, 19 Feb 2019 10:04:54 -0600
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Subject: Re: [Qemu-devel] [PATCH 11/12] block: Use normal drain for
 bdrv_set_aio_context()
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To: Kevin Wolf <kwolf@redhat.com>
Cc: qemu-block@nongnu.org, mreitz@redhat.com, stefanha@redhat.com, berrange@redhat.com, pbonzini@redhat.com, qemu-devel@nongnu.org

On 2/19/19 5:23 AM, Kevin Wolf wrote:
> Am 18.02.2019 um 21:57 hat Eric Blake geschrieben:
>> On 2/18/19 10:18 AM, Kevin Wolf wrote:
>>> Now that bdrv_set_aio_context() works inside drained sections, it can
>>> also use the real drain function instead of open coding something
>>> similar.
>>>
>>> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
>>> ---

>>> +/* The caller must own the AioContext lock for the old AioContext of bs, but it
>>> + * must not own the AioContext lock for new_context. */
>>
>> Is this comment still accurate, given
>>
>>>  void bdrv_set_aio_context(BlockDriverState *bs, AioContext *new_context)
>>>  {
>>> -    AioContext *ctx = bdrv_get_aio_context(bs);
>>> -
>>> -    if (ctx == new_context) {
>>> +    if (bdrv_get_aio_context(bs) == new_context) {
>>>          return;
>>>      }
>>
>> the short-circuiting when the old context is the new context?
> 
> Hm, yes, old == new is an exception where you quite obviously can't have
> old locked and new unlocked at the same time.
> 
> So is adding this enough?
> 
>     (unless new_context is the same as the current context of bs)

Works for me.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org