linux-kernel - Re: [RFC PATCH 0/3] introduce PIDFD

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Message-ID: <87ttdxl9ch.fsf@oldenburg.str.redhat.com>
Date: Mon, 30 Sep 2024 12:33:18 +0200
From: Florian Weimer <fweimer@...hat.com>
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
Subject: Re: [RFC PATCH 0/3] introduce PIDFD_SELF

* Lorenzo Stoakes:

> If you wish to utilise a pidfd interface to refer to the current process
> (from the point of view of userland - from the kernel point of view - the
> thread group leader), it is rather cumbersome, requiring something like:
>
> 	int pidfd = pidfd_open(getpid(), 0);
>
> 	...
>
> 	close(pidfd);
>
> Or the equivalent call opening /proc/self. It is more convenient to use a
> sentinel value to indicate to an interface that accepts a pidfd that we
> simply wish to refer to the current process.

The descriptor will refer to the current thread, not process, right?

The distinction matters for pidfd_getfd if a process contains multiple
threads with different file descriptor tables, and probably for
pidfd_send_signal as well.

Thanks,
Florian