linux-kernel - Re: [PATCH v2 0/2] vfs: Define new syscall getumask.

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Message-ID: <20160414021348.GB16656@thunk.org>
Date:	Wed, 13 Apr 2016 22:13:48 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	"Richard W.M. Jones" <rjones@...hat.com>,
	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	mingo@...hat.com, "H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>, luto@...nel.org,
	viro@...iv.linux.org.uk, zab <zab@...hat.com>, emunson@...mai.com,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Andrea Arcangeli <aarcange@...hat.com>, josh@...htriplett.org,
	Pavel Emelyanov <xemul@...allels.com>, sfr@...b.auug.org.au,
	Milosz Tanski <milosz@...in.com>,
	rostedt <rostedt@...dmis.org>, arnd@...db.de,
	ebiederm@...ssion.com, gorcunov <gorcunov@...nvz.org>,
	iulia manda21 <iulia.manda21@...il.com>,
	dave hansen <dave.hansen@...ux.intel.com>,
	mguzik <mguzik@...hat.com>, adobriyan@...il.com,
	Davidlohr Bueso <dave@...olabs.net>,
	linux-api <linux-api@...r.kernel.org>, gorcunov@...il.com,
	fw@...eb.enyo.de, Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2 0/2] vfs: Define new syscall getumask.

On Wed, Apr 13, 2016 at 09:01:25PM +0000, Mathieu Desnoyers wrote:
> I'm actually discussing 3 separate things here: the umask, sigmask, and
> cpu affinity mask.

The last two are available in /proc/<pid>/status --- which brings up
the question why not just add umask to /proc/<pid>/status?

That way the shared library can read it via /proc/self/status, but
this way it would be possible to look at other process's umask values
this as well.

> >> Another approach to this has been attempted before, adding something
> >> to /proc, although it didn't go anywhere.  See:
> >> 
> >>  http://comments.gmane.org/gmane.linux.kernel/1292109

... and indeed that's what I suggested.  It looks like from the thread
that it petered out due to apathy instead of people not liking the
idea.

One other reason to suggest using a /proc file is that you're not at
the mercy of the glibc folks to wire up a new system call.  (Glibc has
been refusing to wire up getrandom(2), for example.   Grrrr.....)

     	      	      	 	       	   	      - Ted