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

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Message-ID: <35ipnq7dik6skpgrsywtje734iam65h2zjsv7fv5ayzfwnjlph@odu2szclos5y>
Date: Wed, 23 Oct 2024 10:18:28 -0700
From: Shakeel Butt <shakeel.butt@...ux.dev>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
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 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?