Re: [PATCH v6 25/33] block_int-common.h: split function pointers in BdrvChildClass

[Emanuele Giuseppe Esposito]

On 26/01/2022 13:42, Hanna Reitz wrote:
> On 21.01.22 18:05, Emanuele Giuseppe Esposito wrote:
>> Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
>> ---
>>   include/block/block_int-common.h | 67 +++++++++++++++++++-------------
>>   1 file changed, 40 insertions(+), 27 deletions(-)
>>
>> diff --git a/include/block/block_int-common.h
>> b/include/block/block_int-common.h
>> index e007dbf768..cc8c8835ba 100644
>> --- a/include/block/block_int-common.h
>> +++ b/include/block/block_int-common.h
>> @@ -815,12 +815,16 @@ struct BdrvChildClass {
>>        */
>>       bool parent_is_bds;
>>   +    /*
>> +     * Global state (GS) API. These functions run under the BQL lock.
>> +     *
>> +     * See include/block/block-global-state.h for more information about
>> +     * the GS API.
>> +     */
>>       void (*inherit_options)(BdrvChildRole role, bool parent_is_format,
>>                               int *child_flags, QDict *child_options,
>>                               int parent_flags, QDict *parent_options);
>> -
>>       void (*change_media)(BdrvChild *child, bool load);
>> -    void (*resize)(BdrvChild *child);
>>         /*
>>        * Returns a name that is supposedly more useful for human users
>> than the
> 
> The method this comment belongs to is `.get_name()`.  It’s exposed
> through `bdrv_get_parent_name()`, which is called by
> `bdrv_get_device_name()` and `bdrv_get_device_or_node_name()` – so I
> think it should be classified as I/O.

Agree on this, and also on comment on patch 23 about bdrv_probe.
> 
>> @@ -837,6 +841,40 @@ struct BdrvChildClass {
>>        */
>>       char *(*get_parent_desc)(BdrvChild *child);
> 
> This function is very similar, so we might also want to reconsider
> classifying it as I/O.  There’s no need, because all of its callers do
> run in the main thread, but at the same time I don’t believe there’s
> anything stopping us (and it starts to sound to me like all functions of
> the “get name” kind perhaps should ideally be I/O, in that they
> shouldn’t require the GS context).
> 
> Up to you. O:)

I understand what you mean, but I would like to leave it in global
state. Seeing the assertion/definition as GS tells me that it is already
under BQL, and I should not worry about I/O in that function. If no such
assert was present, it would lead me to think that there might be I/O
concurrently using it, and complicate the logic of whatever I want to do
there.

Thank you,
Emanuele

> 
> (Rest of this patch looks good!)
> 
> Hanna
>