# Re: \[PATCH v3 3/7\] shm: add memfd\_create() syscall - From: David Herrmann \ - Date: 2014-06-13 12:41:24 - List: linux-api - Page: https://ratatoskr.run/linux-api/2014/06/85596 - Thread: https://ratatoskr.run/linux-mm/2014/06/85586/t.md ```text Hi On Fri, Jun 13, 2014 at 2:27 PM, Michael Kerrisk (man-pages) [ref] wrote: > Hi David, > > On Fri, Jun 13, 2014 at 12:36 PM, David Herrmann [ref] 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 ```