linux-kernel - Re: [PATCH v4 2/4] pidfd: add PIDFD_SELF_* sentinels to refer to own thread/process

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Message-ID: <4ce07818-1adf-42eb-9c0a-85f231a5648b@lucifer.local>
Date: Wed, 23 Oct 2024 18:24:00 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Christian Brauner <christian@...uner.io>, Shuah Khan <shuah@...nel.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>, pedro.falcato@...il.com,
        linux-kselftest@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
        linux-kernel@...r.kernel.org, Oliver Sang <oliver.sang@...el.com>,
        John Hubbard <jhubbard@...dia.com>
Subject: Re: [PATCH v4 2/4] pidfd: add PIDFD_SELF_* sentinels to refer to own
 thread/process

On Wed, Oct 23, 2024 at 10:18:28AM -0700, Shakeel Butt wrote:
> On Wed, Oct 23, 2024 at 08:18:35AM GMT, Lorenzo Stoakes wrote:
> > On Tue, Oct 22, 2024 at 05:53:00PM -0700, Shakeel Butt wrote:
> > > On Thu, Oct 17, 2024 at 10:05:50PM GMT, Lorenzo Stoakes wrote:
> > > > It is useful to be able to utilise the pidfd mechanism to reference the
> > > > current thread or process (from a userland point of view - thread group
> > > > leader from the kernel's point of view).
> > > >
> > > > Therefore introduce PIDFD_SELF_THREAD to refer to the current thread, and
> > > > PIDFD_SELF_THREAD_GROUP to refer to the current thread group leader.
> > > >
> > > > For convenience and to avoid confusion from userland's perspective we alias
> > > > these:
> > > >
> > > > * PIDFD_SELF is an alias for PIDFD_SELF_THREAD - This is nearly always what
> > > >   the user will want to use, as they would find it surprising if for
> > > >   instance fd's were unshared()'d and they wanted to invoke pidfd_getfd()
> > > >   and that failed.
> > > >
> > > > * PIDFD_SELF_PROCESS is an alias for PIDFD_SELF_THREAD_GROUP - Most users
> > > >   have no concept of thread groups or what a thread group leader is, and
> > > >   from userland's perspective and nomenclature this is what userland
> > > >   considers to be a process.
> > >
> > > Should users use PIDFD_SELF_PROCESS in process_madvise() for self
> > > madvise() (once the support is added)?
> >
> > You can use either it will make no difference as both will get you to
> > current->mm which has to be shared. So I'd go with PIDFD_SELF for brevity
> > :)
> >
> > This series and the prerequisites I already added to process_madvise()
> > already provide support so with this in you can just use this for that.
>
> Thanks a lot, this is awesome. Is the plan for this series to go through
> mm-tree or through Christian?
>

Thanks!

I am assuming this will go through Christian's tree as entirely within the
pidfd realm :)

Christian - I am assuming this is your expectation too right?

I cc'd linux-mm more for convenience as obviously am hoping to use this for
an mm thing myself.