linux-kernel - [PATCH] procfs: expose umask in /proc/<PID>/status (formerly umask2, formerly getumask)

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Date:	Thu, 14 Apr 2016 10:34:48 +0100
From:	"Richard W.M. Jones" <rjones@...hat.com>
To:	corbet@....net
Cc:	akpm@...ux-foundation.org, vbabka@...e.cz, mhocko@...e.com,
	hughd@...gle.com, koct9i@...il.com, chenhanxiao@...fujitsu.com,
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Subject: [PATCH] procfs: expose umask in /proc/<PID>/status (formerly umask2, formerly getumask)

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.