Re: [Qemu-devel] [PATCH v3 3/5] block: qobject_is_equal() in bdrv_reopen_prepare()

[Max Reitz <mreitz@redhat.com>]

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On 2017-07-03 14:51, Eric Blake wrote:
> On 07/03/2017 07:25 AM, Max Reitz wrote:
>> Currently, bdrv_reopen_prepare() assumes that all BDS options are
>> strings. However, this is not the case if the BDS has been created
>> through the json: pseudo-protocol or blockdev-add.
>>
>> Note that the user-invokable reopen command is an HMP command, so you
> 
> s/invokable/invocable/

I was asking this myself when writing this commit message and actually
consulted Wiktionary: https://en.wiktionary.org/wiki/invokable

>> can only specify strings there. Therefore, specifying a non-string
>> option with the "same" value as it was when originally created will now
>> return an error because the values are supposedly similar (and there is
>> no way for the user to circumvent this but to just not specify the
>> option again -- however, this is still strictly better than just
>> crashing).
>>
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>> ---
>>  block.c | 31 ++++++++++++++++++-------------
>>  1 file changed, 18 insertions(+), 13 deletions(-)
>>
> 
>> +            /* TODO: When using -drive to specify blockdev options, all values
>> +             * will be strings; however, when using -blockdev, blockdev-add or
>> +             * filenames using the json:{} pseudo-protocol, they will be
>> +             * correctly typed.
>> +             * In contrast, reopening options are (currently) always strings
>> +             * (because you can only specify them through qemu-io; all other
>> +             * callers do not specify any options).
>> +             * Therefore, when using anything other than -drive to create a BDS,
>> +             * this cannot detect non-string options as unchanged, because
>> +             * qobject_is_equal() always returns false for objects of different
>> +             * type.  In the future, this should be remedied by correctly typing
>> +             * all options.  For now, this is not too big of an issue because
>> +             * the user simply can not specify options which cannot be changed
> 
> Seeing "can not" usually looks wrong for "cannot"; but here, it is
> grammatically correct.  But better would be "the user can simply not
> specify" or "the user can simply avoid specifying options".

Awww, I deliberately designed the sentence so I could use "can not". :-)

(and even contrast it with the following "cannot"!)

>> +             * anyway, so they will stay unchanged. */
> 
> The grammar tweak is minor, so:
> Reviewed-by: Eric Blake <eblake@redhat.com>
Please let me keep it :-)

Max


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