Re: [RESEND PATCH v4 09/15] fs/resctrl: Introduce kmode_cpus/kmode_cpus_list per rdtgroup

[Reinette Chatre]

Hi Babu,

On 8/13/26 10:57 AM, Babu Moger wrote:
> Hi Reinette,
> 
> On 8/10/26 22:20, Reinette Chatre wrote:
>> Hi Babu,
>>
>> On 7/7/26 2:50 PM, Babu Moger wrote:
>>> Kernel-mode resctrl policies allow kernel work to be associated with a
>>> specific rdtgroup, optionally restricted to a subset of online CPUs.
>>>
>>> While user space can query the active kernel-mode policy and its associated
>>> rdtgroup through info/kernel_mode, it currently lacks visibility into the
>>> CPU scope of that binding.
>>>
>>> Introduce read-only kmode_cpus and kmode_cpus_list files for each rdtgroup.
>>
>> I think it will be easier to follow if this is deferred to not create these
>> files in all resource groups by default. Instead, at the time they are
>> created it should be obvious that they will only be visible in resource group
>> associated with the active kernel mode.
> 
> I am not clear on this comment. Do you mean create these files when user associates the group to kernel mode? (during rdtgroup_config_kmode)

No. As this changelog states it creates these files in all resource groups. This
is a confusing thing to do at this point in the series since these files are not
expected to be present/visible in all resource groups, only in a resource group that
is assigned to the "global" kernel mode. This commit mentions nothing about this
usage and thus from reader perspective does not seem like the right thing to do here.

> 
> Also, you mentioned about rftype::create_hidden in
> https://lore.kernel.org/lkml/0126a5e5-48cf-416f-a21b-c231a703c18b@xxxxxxxxx/
> 
> Can you please clarify on this?

resctrl has centralized functions to create files. For example, rdtgroup_add_file()
that takes as parameter the properties of the file, struct rftype. With a new
property, for example rftype::create_hidden the file's default visibility can be
set _at the time it is created_. This simplifies the code by not needing to sprinkle
changes to these files' visibility after the fact at the various places files are created.

One patch can add capability to resctrl to have a file property indicating that the
file should essentially be created with KERNFS_HIDDEN set.

This patch can then follow by using the capability to create the kmode_cpus and
kmode_cpus_list files in all resource groups and it will be clear that the files
are not exposed to user space by default.

Reinette