Re: [PATCH V2] xen/arm: dm: Drop XEN_DMOP_get_ioreq_server_info from supported

["Orzel, Michal" <michal.orzel@xxxxxxx>]

On 02/09/2025 13:54, Julien Grall wrote:
> Hi,
> 
> On 02/09/2025 11:18, Orzel, Michal wrote:
>>
>>
>> On 02/09/2025 11:49, Oleksandr Tyshchenko wrote:
>>> The said sub-op is not supported on Arm, since it:
>>>   - does not support the buffered emulation (so bufioreq_port/bufioreq_gfn
>>>     cannot be returned), please refer to ioreq_server_create()
>>>   - does not support "legacy" mechanism of mapping IOREQ Server
>>>     magic pages (so ioreq_gfn/bufioreq_gfn cannot be returned), please
>>>     refer to arch_ioreq_server_map_pages(). On Arm, only the Acquire
>>>     Resource infrastructure is used to query and map the IOREQ Server pages.
>>>
>>> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
>> Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
>>
>> Could we perhaps add a Fixes tag here pointing to the commit introducing 
>> these
>> DM ops and thus add this patch for this release? Not sure what others think.
> 
> Fixes usually implies a bug and I don't see what bug we are solving. In 
> fact, I don't understand why we are trying to remove the subop...
Hmm, the issue is that the subop that is not supported at the moment is listed
as supported in the public header. I think if we mistakenly mention sth as
supported in e.g. SUPPORT.md we would have no issues adding a Fixes tag. There
are many cases where Fixes was used just to change something in a comment, so
I'm having a hard time reasoning about when it's appropriate to use it. As for
the code, from safety perspective if this subop is listed explicilty in Arm's
dm.c, we would need to write a separate test case and test to cover it that at
the end, still returns -EOPNOTSUPP.

~Michal