Re: [Qemu-block] [PATCH v20 13/30] block: new bdrv_reopen_bitmaps_rw interface

[Max Reitz]

On 2017-06-14 11:03, Vladimir Sementsov-Ogievskiy wrote:
> 13.06.2017 18:28, Max Reitz wrote:
>> On 2017-06-13 12:25, Vladimir Sementsov-Ogievskiy wrote:
>>> 09.06.2017 16:27, Max Reitz wrote:
>>>> On 2017-06-02 13:21, Vladimir Sementsov-Ogievskiy wrote:
>>>>> Add format driver handler, which should mark loaded read-only
>>>>> bitmaps as 'IN_USE' in the image and unset read_only field in
>>>>> corresponding BdrvDirtyBitmap's.
>>>>>
>>>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <address@hidden>
>>>>> ---
>>>>>    block.c                   | 17 +++++++++++++++++
>>>>>    include/block/block_int.h |  7 +++++++
>>>>>    2 files changed, 24 insertions(+)
>>>>>
>>>>> diff --git a/block.c b/block.c
>>>>> index 04af7697dc..161db9e32a 100644
>>>>> --- a/block.c
>>>>> +++ b/block.c
>>>>> @@ -2946,12 +2946,16 @@ void bdrv_reopen_commit(BDRVReopenState
>>>>> *reopen_state)
>>>>>    {
>>>>>        BlockDriver *drv;
>>>>>        BlockDriverState *bs;
>>>>> +    bool old_can_write, new_can_write;
>>>>>          assert(reopen_state != NULL);
>>>>>        bs = reopen_state->bs;
>>>>>        drv = bs->drv;
>>>>>        assert(drv != NULL);
>>>>>    +    old_can_write =
>>>>> +        !bdrv_is_read_only(bs) && !(bdrv_get_flags(bs) &
>>>>> BDRV_O_INACTIVE);
>>>>> +
>>>>>        /* If there are any driver level actions to take */
>>>>>        if (drv->bdrv_reopen_commit) {
>>>>>            drv->bdrv_reopen_commit(reopen_state);
>>>>> @@ -2965,6 +2969,19 @@ void bdrv_reopen_commit(BDRVReopenState
>>>>> *reopen_state)
>>>>>        bs->read_only = !(reopen_state->flags & BDRV_O_RDWR);
>>>>>          bdrv_refresh_limits(bs, NULL);
>>>>> +
>>>>> +    new_can_write =
>>>>> +        !bdrv_is_read_only(bs) && !(bdrv_get_flags(bs) &
>>>>> BDRV_O_INACTIVE);
>>>>> +    if (!old_can_write && new_can_write &&
>>>>> drv->bdrv_reopen_bitmaps_rw) {
>>>>> +        Error *local_err = NULL;
>>>>> +        if (drv->bdrv_reopen_bitmaps_rw(bs, &local_err) < 0) {
>>>>> +            /* This is not fatal, bitmaps just left read-only, so
>>>>> all following
>>>>> +             * writes will fail. User can remove read-only bitmaps
>>>>> to unblock
>>>>> +             * writes.
>>>>> +             */
>>>> In a sense, it pretty much is fatal. We were asked to make the image
>>>> non-read-only but we failed because it effectively still is read-only.
>>>>
>>>> But I can't think of anything better, and you're right, removing the
>>>> bitmaps would resolve the situation. This would require the user to
>>>> know
>>>> that updating the bitmaps was the issue, and local_err may not actually
>>>> reflect that.
>>>>
>>>>> +            error_report_err(local_err);
>>>> So I'd prepend this with something like "$node_name: Failed to make
>>>> dirty bitmaps writable", and maybe append a hint like "Removing all
>>>> persistent dirty bitmaps from this node will allow writing to it".
>>> Ok for prepending, but I don't want to add last note, as for the user it
>>> may better to retry an operation, leading reopening image rw..
>> Which operation do you mean? The reopening? Because that operation
>> already "succeeded" at this point, so you can't retry it...
> 
> So, firstly, reopen r-o again and then reopen r-w? Is it possible?

That should work, yes -- if it works then. :-)

Max

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