From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f170.google.com (mail-ig0-f170.google.com [209.85.213.170]) by kanga.kvack.org (Postfix) with ESMTP id 792146B00BD for ; Fri, 13 Jun 2014 08:41:25 -0400 (EDT) Received: by mail-ig0-f170.google.com with SMTP id h3so1493878igd.3 for ; Fri, 13 Jun 2014 05:41:25 -0700 (PDT) Received: from mail-ie0-x230.google.com (mail-ie0-x230.google.com [2607:f8b0:4001:c03::230]) by mx.google.com with ESMTPS id ce6si6623476icc.61.2014.06.13.05.41.24 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Fri, 13 Jun 2014 05:41:24 -0700 (PDT) Received: by mail-ie0-f176.google.com with SMTP id rd18so2434695iec.35 for ; Fri, 13 Jun 2014 05:41:24 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <1402655819-14325-1-git-send-email-dh.herrmann@gmail.com> <1402655819-14325-4-git-send-email-dh.herrmann@gmail.com> Date: Fri, 13 Jun 2014 14:41:24 +0200 Message-ID: Subject: Re: [PATCH v3 3/7] shm: add memfd_create() syscall From: David Herrmann Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org List-ID: To: Michael Kerrisk-manpages Cc: lkml , Ryan Lortie , Linus Torvalds , Andrew Morton , "linux-mm@kvack.org" , "linux-fsdevel@vger.kernel.org" , Linux API , Greg Kroah-Hartman , John Stultz , Lennart Poettering , Daniel Mack , Kay Sievers , Hugh Dickins , Tony Battersby , Andy Lutomirski Hi On Fri, Jun 13, 2014 at 2:27 PM, Michael Kerrisk (man-pages) wrote: > Hi David, > > On Fri, Jun 13, 2014 at 12:36 PM, David Herrmann wrote: >> memfd_create() is similar to mmap(MAP_ANON), but returns a file-descriptor >> that you can pass to mmap(). It can support 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() returns the raw shmem file, so calls like ftruncate() can >> be used to modify the underlying inode. Also calls like fstat() >> will return proper information and mark the file as regular file. If you >> want sealing, you can specify MFD_ALLOW_SEALING. Otherwise, sealing is not >> supported (like on all other regular files). >> >> Compared to O_TMPFILE, it does not require a tmpfs mount-point and is not >> subject to quotas and alike. It is still properly accounted to memcg >> limits, though. > > Where do I find / is there detailed documentation (ideally, a man > page) for this new system call? I did write a man-page proposal for memfd_create() and a patch for fcntl() for v1, however, the API changed several times so I didn't keep them up to date (the man-page patches are on LKML). However, I wrote a short introduction to memfd+sealing v3, that I recommend reading first: http://dvdhrm.wordpress.com/2014/06/10/memfd_create2/ This explains the idea behind the new API and describes almost all aspects of it. It's up-to-date to v3 and I will use it to write the final man-pages once Hugh and Andrew ACKed the patches. Let me know if anything is unclear. Thanks for looking at it! David -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org