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

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Date:	Wed, 13 Apr 2016 11:41:45 -0400
From:	Colin Walters <walters@...bum.org>
To:	"Richard W.M. Jones" <rjones@...hat.com>,
	linux-kernel@...r.kernel.org
Cc:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	akpm@...ux-foundation.org, luto@...nel.org,
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	zab@...hat.com, emunson@...mai.com, paulmck@...ux.vnet.ibm.com,
	aarcange@...hat.com, josh@...htriplett.org, xemul@...allels.com,
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	arnd@...db.de, ebiederm@...ssion.com, gorcunov@...nvz.org,
	iulia.manda21@...il.com, dave.hansen@...ux.intel.com,
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	linux-api@...r.kernel.org, gorcunov@...il.com, fw@...eb.enyo.de
Subject: Re: [PATCH v2 0/2] vfs: Define new syscall getumask.

On Wed, Apr 13, 2016, at 08:57 AM, Richard W.M. Jones wrote:

> 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.

I assume you just want to do this from a shared library so you can
determine whether or not you need to call fchown() after making files
and the like?  If that's the case it'd be good to note it in the commit
message.

BTW...it might be a good idea to add a flags argument:
https://lwn.net/Articles/585415/

Did you consider calling this `umask2`, having the initial version only support
retrieving it via a UMASK_GET flag, and lay the groundwork to support
setting a threadsafe umask with a UMASK_SET_THREAD flag?