linux-kernel - Re: [PATCH 3/6] shm: add memfd

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Message-ID: <20140320084748.GK1728@moon>
Date:	Thu, 20 Mar 2014 12:47:48 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	David Herrmann <dh.herrmann@...il.com>,
	Pavel Emelyanov <xemul@...allels.com>
Cc:	linux-kernel@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Matthew Wilcox <matthew@....cx>,
	Karol Lewandowski <k.lewandowsk@...sung.com>,
	Kay Sievers <kay@...y.org>, Daniel Mack <zonque@...il.com>,
	Lennart Poettering <lennart@...ttering.net>,
	Kristian Høgsberg <krh@...planet.net>,
	john.stultz@...aro.org, Greg Kroah-Hartman <greg@...ah.com>,
	Tejun Heo <tj@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	dri-devel@...ts.freedesktop.org, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ryan Lortie <desrt@...rt.ca>,
	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Subject: Re: [PATCH 3/6] shm: add memfd_create() syscall

On Wed, Mar 19, 2014 at 08:06:48PM +0100, David Herrmann wrote:
> memfd_create() is similar to mmap(MAP_ANON), but returns a file-descriptor
> that you can pass to mmap(). It explicitly allows sealing and
> avoids any connection to user-visible mount-points. Thus, it's not
> subject to quotas on mounted file-systems, but can be used like
> malloc()'ed memory, but with a file-descriptor to it.
> 
> memfd_create() does not create a front-FD, but instead returns the raw
> shmem file, so calls like ftruncate() can be used. Also calls like fstat()
> will return proper information and mark the file as regular file. Sealing
> is explicitly supported on memfds.
> 
> Compared to O_TMPFILE, it does not require a tmpfs mount-point and is not
> subject to quotas and alike.

If I'm not mistaken in something obvious, this looks similar to /proc/pid/map_files
feature, Pavel?
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