Re: [RFC PATCH v2 bpf-next 0/3] bpf: cgroup: support writing and freezing cgroups from BPF

[Tejun Heo <tj@kernel.org>]

Hello,

On Fri, Aug 22, 2025 at 07:16:15PM +0100, Djalal Harouni wrote:
...
> I do realize taking the same usual path with write is the obvious thing,
> but we don't have the corresponding open context, and faking it seems
> more trouble than calling directly cgroup backends...
> 
> Allow me please to do it again directly on cgroup_base_file[] assuming
> it was Alexei suggestion and see how it looks.

I'm probably missing something but what prevents you from getting a dentry
from kernfs_node and then calling vfs_open() on it and then do vfs_write()
on the returned file?

If there are some fundamental reasons that we can't do something like that,
let's go back to the simple approach where we just have bpf helpers for
freezing and unfreezing cgroups outside of fs interface.

> Also Tejun, could you please point me to extra cgroup or kernfs tests
> you run? much appreciated!

I'm afraid there isn't much outside what's in the selftest directory.

Thanks.

-- 
tejun