linux-kernel - Re: [PATCH v2 2/3] shm: add memfd

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Date:	Wed, 21 May 2014 14:50:19 +0400
From:	Konstantin Khlebnikov <koct9i@...il.com>
To:	David Herrmann <dh.herrmann@...il.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Ryan Lortie <desrt@...rt.ca>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Tejun Heo <tj@...nel.org>, Greg Kroah-Hartman <greg@...ah.com>,
	John Stultz <john.stultz@...aro.org>,
	Kristian Høgsberg <krh@...planet.net>,
	Lennart Poettering <lennart@...ttering.net>,
	Daniel Mack <zonque@...il.com>, Kay Sievers <kay@...y.org>
Subject: Re: [PATCH v2 2/3] shm: add memfd_create() syscall

On Tue, Apr 15, 2014 at 10:38 PM, David Herrmann <dh.herrmann@...il.com> 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() 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. If you
> want sealing, you can specify MFD_ALLOW_SEALING. Otherwise, sealing is not
> support (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.
>
> Signed-off-by: David Herrmann <dh.herrmann@...il.com>
> ---

<cut>

> +++ b/include/linux/syscalls.h
> @@ -802,6 +802,7 @@ asmlinkage long sys_timerfd_settime(int ufd, int flags,
>  asmlinkage long sys_timerfd_gettime(int ufd, struct itimerspec __user *otmr);
>  asmlinkage long sys_eventfd(unsigned int count);
>  asmlinkage long sys_eventfd2(unsigned int count, int flags);
> +asmlinkage long sys_memfd_create(const char *uname_ptr, u64 size, u64 flags);

Is it right to use u64 here? I think arguments sould be 'loff_t' and 'int'.

>  asmlinkage long sys_fallocate(int fd, int mode, loff_t offset, loff_t len);
>  asmlinkage long sys_old_readdir(unsigned int, struct old_linux_dirent __user *, unsigned int);
>  asmlinkage long sys_pselect6(int, fd_set __user *, fd_set __user *,
--
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