On 03/20/2014 12:47 PM, Cyrill Gorcunov wrote:
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?
Thanks, Cyrill.
It is, but the map_files will work "in the opposite direction" :) In the memfd case one first gets an FD, then mmap()s it; in the /proc/pis/map_files case one should first mmap() a region, then open it via /proc/self/map_files.
But I don't know whether this matters.
Thanks, Pavel