Re: [Qemu-devel] [for-2.9 4/8] block: Document -drive problematic code and bugs

[Max Reitz]

On 30.03.2017 16:42, Markus Armbruster wrote:
> Eric Blake <address@hidden> writes:
> 
>> On 03/30/2017 01:52 AM, Markus Armbruster wrote:
>>
>>>>> +++ b/block.c
>>>>> @@ -1157,6 +1157,12 @@ static int bdrv_open_common(BlockDriverState *bs, 
>>>>> BlockBackend *file,
>>>>>      if (file != NULL) {
>>>>>          filename = blk_bs(file)->filename;
>>>>>      } else {
>>>>> +       /*
>>>>> +        * Caution: direct use of non-string @options members is
>>>>> +        * problematic.  When they come from -blockdev or blockdev_add,
>>>>> +        * members are typed according to the QAPI schema, but when
>>>>> +        * they come from -drive, they're all QString.
>>>>> +        */
>>>>>          filename = qdict_get_try_str(options, "filename");
>>>>
>>>> For instance this one: Well, yes, for -drive, this will always be a
>>>> QString. Which is OK, because that's what we're trying to get.
>>>>
>>>> The comment makes this confusing, IMO. If you really want a comment here
>>>> it should at least contain a mention that it's totally fine in practice
>>>> here. Calling the code "problematic" sounds like this could blow up when
>>>> it reality it can't; and I would think it actually is the most sane
>>>> solution given the current state of the whole infrastructure (i.e. how
>>>> -drive and -blockdev work).
>>>
>>> Well, if it could blow up, I'd call it wrong, and start the comment with
>>> FIXME :)
>>>
>>> Even though qdict_get_try_str() is indeed fine, I propose to have a
>>> comment, because someone with less detailed understanding of how the
>>> configuration machine works (me, until yesterday, and probably again
>>> after next month) could conclude that qdict_get_try_bool() would be just
>>> as fine.
>>>
>>> What about:
>>>
>>>    /*
>>>     * Caution: while qdict_get_try_str() is fine, getting non-string
>>>     * types would require more care.  When @options come from -blockdev
>>>     * or blockdev_add, its members are typed according to the QAPI
>>>     * schema, but when they come from -drive, they're all QString.
>>>     */
>>
>> Yes, that's better - it makes it obvious that our current usage works,
>> but that the code must not be carelessly edited if we add another field
>> in the future.
> 
> If Max is also happy with it, I'll put it in v3.

Yes, more than happy, thanks! (Same for the other comment.)

Max

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