shm: add memfd_create() syscall (9183df25) · Commits · 戴 / test

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 a filesystem size limit. It is still properly accounted to memcg limits, though, and to the same overcommit or no-overcommit accounting as all user memory. Signed-off-by:

David Herrmann <dh.herrmann@gmail.com> Acked-by:

Hugh Dickins <hughd@google.com> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Ryan Lortie <desrt@desrt.ca> Cc: Lennart Poettering <lennart@poettering.net> Cc: Daniel Mack <zonque@gmail.com> Cc: Andy Lutomirski <luto@amacapital.net> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

arch/x86/syscalls/syscall_32.tbl

+1 −0

Original line number	Diff line number	Diff line
		@@ -362,3 +362,4 @@
		353 i386 renameat2 sys_renameat2
		354 i386 seccomp sys_seccomp
		355 i386 getrandom sys_getrandom
		356 i386 memfd_create sys_memfd_create

arch/x86/syscalls/syscall_64.tbl

+1 −0

Original line number	Diff line number	Diff line
		@@ -325,6 +325,7 @@
		316 common renameat2 sys_renameat2
		317 common seccomp sys_seccomp
		318 common getrandom sys_getrandom
		319 common memfd_create sys_memfd_create

		#
		# x32-specific system call numbers start at 512 to avoid cache impact

include/linux/syscalls.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -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 __user *uname_ptr, unsigned int flags);
		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 ,

include/uapi/linux/memfd.h

0 → 100644

+8 −0

Original line number	Diff line number	Diff line
		#ifndef _UAPI_LINUX_MEMFD_H
		#define _UAPI_LINUX_MEMFD_H

		/* flags for memfd_create(2) (unsigned int) */
		#define MFD_CLOEXEC 0x0001U
		#define MFD_ALLOW_SEALING 0x0002U

		#endif /* _UAPI_LINUX_MEMFD_H */

kernel/sys_ni.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -197,6 +197,7 @@ cond_syscall(compat_sys_timerfd_settime);
		cond_syscall(compat_sys_timerfd_gettime);
		cond_syscall(sys_eventfd);
		cond_syscall(sys_eventfd2);
		cond_syscall(sys_memfd_create);

		/* performance counters: */
		cond_syscall(sys_perf_event_open);

Admin message