Re: [RFC PATCH 3/7] resctrl: Add a devices file for external requester assignment

Hi Drew,

On 8/12/26 10:19 AM, Drew Fustini wrote:
> On Tue, Jul 14, 2026 at 09:06:53PM +0800, Zhanpeng Zhang wrote:
>> Do not overload the resctrl tasks file with architecture-specific
>> non-PID tokens. The tasks ABI remains a list of task IDs, while the new
>> devices file carries external requesters assigned to a resctrl group.
>>
>> Add architecture hooks for assigning and showing those external
>> objects, and reject group removal, reparenting, or pseudo-lock setup
>> while devices are still assigned. The teardown path performs a
>> best-effort reset to the default group.
>>
>> The devices file is an assignment interface only. It does not describe
>> a new resource schema or domain; resource allocation and monitoring
>> policy remain described by the existing schemata and info files.
>>
>> Signed-off-by: Zhanpeng Zhang <[email protected]>
>> ---
>>   Documentation/filesystems/resctrl.rst |  26 ++++
>>   arch/Kconfig                          |   6 +
>>   fs/resctrl/rdtgroup.c                 | 206 +++++++++++++++++++++++++-
>>   include/linux/resctrl.h               |  45 ++++++
>>   4 files changed, 280 insertions(+), 3 deletions(-)
> [..]
>> diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
>> index af2cbab14497..2e424c911049 100644
>> --- a/fs/resctrl/rdtgroup.c
>> +++ b/fs/resctrl/rdtgroup.c
> [..]
>> @@ -2067,6 +2236,16 @@ static struct rftype res_common_files[] = {
>>   		.seq_show	= rdtgroup_tasks_show,
>>   		.fflags		= RFTYPE_BASE,
>>   	},
>> +#ifdef CONFIG_ARCH_HAS_RESCTRL_DEVICES
>> +	{
>> +		.name		= "devices",
>> +		.mode		= 0644,
>> +		.kf_ops		= &rdtgroup_kf_single_ops,
>> +		.write		= rdtgroup_devices_write,
>> +		.seq_show	= rdtgroup_devices_show,
>> +		.fflags		= RFTYPE_BASE,
>
> Once CONFIG_ARCH_HAS_RESCTRL_DEVICES is built in, the file shows up in
> every resctrl group directory, even on hardware whose IOMMU does not
> implement QOSID. I think it would be better to make fflags zero so
> rdtgroup_add_files() skips it, and enable it at runtime from
> resctrl_init().
>
> Thanks,
> Drew

Good point. The build-time architecture capability is not sufficient to
expose the file. I will look for an appropriate runtime mechanism to
control whether the file is exposed.

Thank you for the careful review. I really appreciate it.

Thanks,
Zhanpeng