From: "Richard W.M. Jones" <rjones@redhat.com>
To: corbet@lwn.net
Cc: akpm@linux-foundation.org, vbabka@suse.cz, mhocko@suse.com,
        hughd@google.com, koct9i@gmail.com, chenhanxiao@cn.fujitsu.com,
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Subject: [PATCH] procfs: expose umask in /proc/<PID>/status (formerly umask2, formerly getumask)
Date: Thu, 14 Apr 2016 10:34:48 +0100
Message-Id: <1460626489-31932-1-git-send-email-rjones@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 542
Lines: 15

It's not possible to read the process umask without also modifying it,
which is what umask(2) does.  A library cannot read umask safely,
especially if the main program might be multithreaded.

Add a new status line ("Umask") in /proc/<PID>/status.  It contains
the file mode creation mask (umask) in octal.  It is only shown for
tasks which have task->fs.

For the library this allows me to read the umask from
/proc/self/status.

This patch is adapted from one originally written by Pierre Carrier:
https://lkml.org/lkml/2012/5/4/451

Rich.