[PATCH 3/6] shm: add memfd_create() syscall

[Andy Lutomirski]

On 04/02/2014 06:38 AM, Konstantin Khlebnikov wrote:
> On Wed, Mar 19, 2014 at 11:06 PM, David Herrmann <dh.herrmann at gmail.com> 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.
> 
> Instead of adding new syscall we can extend existing openat() a little
> bit more:
> 
> openat(AT_FDSHM, "name", O_TMPFILE | O_RDWR, 0666)

Please don't.  O_TMPFILE is a messy enough API, and the last thing we
need to do is to extend it.  If we want a fancy API for creating new
inodes with no corresponding dentry, let's create one.

Otherwise, let's just stick with a special-purpose API for these shm files.

--Andy