From db9ae076266b4825ad12a67029faa3e7ed125746 Mon Sep 17 00:00:00 2001 From: David Herrmann Date: Wed, 19 Mar 2014 19:03:01 +0100 Subject: memfd_create.2: add memfd_create() man-page The memfd_create() syscall creates anonymous files similar to O_TMPFILE but does not require an active mount-point. Signed-off-by: David Herrmann --- man2/memfd_create.2 | 127 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 127 insertions(+) create mode 100644 man2/memfd_create.2 diff --git a/man2/memfd_create.2 b/man2/memfd_create.2 new file mode 100644 index 000000000..b09042c56 --- /dev/null +++ b/man2/memfd_create.2 @@ -0,0 +1,127 @@ +.\" Copyright (C) 2014 David Herrmann +.\" starting from a version by Michael Kerrisk +.\" +.\" %%%LICENSE_START(GPLv2+_SW_3_PARA) +.\" This program is free software; you can redistribute it and/or modify +.\" it under the terms of the GNU General Public License as published by +.\" the Free Software Foundation; either version 2 of the License, or +.\" (at your option) any later version. +.\" +.\" This program is distributed in the hope that it will be useful, +.\" but WITHOUT ANY WARRANTY; without even the implied warranty of +.\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +.\" GNU General Public License for more details. +.\" +.\" You should have received a copy of the GNU General Public +.\" License along with this manual; if not, see +.\" . +.\" %%%LICENSE_END +.\" +.TH MEMFD_CREATE 2 2014-07-08 Linux "Linux Programmer's Manual" +.SH NAME +memfd_create \- create an anonymous file +.SH SYNOPSIS +.B #include +.sp +.BI "int memfd_create(const char *" name ", unsigned int " flags ");" +.SH DESCRIPTION +.BR memfd_create () +creates an anonymous file and returns a file-descriptor to it. The file behaves +like regular files, thus can be modified, truncated, memory-mapped and more. +However, unlike regular files it lives in main memory and has a volatile +backing storage. Once all references to the file are dropped, it is +automatically released. Anonymous memory is used for all backing pages of the +file. Therefore, they are subject to the same restrictions as other anonymous +memory allocations like +.BR mmap (2) +with +.BR MAP_ANON . + +The initial size of the file is set to 0. +.I name +is used as internal file-name and will occur as such in +.IR /proc/self/fd/ . +The name is always prefixed with +.BR memfd: +and serves only debugging purposes. Names do not affect the behavior of the +memfd, and as such multiple files can have the same name without any side +effects. + +The following values may be bitwise ORed in +.IR flags +to change the behaviour of +.BR memfd_create (): +.TP +.BR MFD_CLOEXEC +Set the close-on-exec +.RB ( FD_CLOEXEC ) +flag on the new file descriptor. +See the description of the +.B O_CLOEXEC +flag in +.BR open (2) +for reasons why this may be useful. Furthermore, +.B O_LARGEFILE +is always set for memfds. +.TP +.BR MFD_ALLOW_SEALING +Allow sealing operations (see +.BR fcntl (2) +with +.B F_ADD_SEALS +and +.BR F_GET_SEALS ) +on this file. The initial set of seals is empty. If this flag is not set, the +initial set of seals will be +.B F_SEAL_SEAL +and as such no other seals can be set on the file. +.PP +Unused bits must be cleared to 0. + +As its return value, +.BR memfd_create () +returns a new file descriptor that can be used to refer to the file. +A copy of the file descriptor created by +.BR memfd_create () +is inherited by the child produced by +.BR fork (2). +The duplicate file descriptor is associated with the same file. +File descriptors created by +.BR memfd_create () +are preserved across +.BR execve (2), +unless the close-on-exec flag has been set. +.SH RETURN VALUE +On success, +.BR memfd_create () +returns a new file descriptor. +On error, \-1 is returned and +.I errno +is set to indicate the error. +.SH ERRORS +.TP +.B EINVAL +An unsupported value was specified in one of the arguments. +.TP +.B EMFILE +The per-process limit on open file descriptors has been reached. +.TP +.B ENFILE +The system-wide limit on the total number of open files has been +reached. +.TP +.B EFAULT +The name given in +.IR name +points to invalid memory. +.TP +.B ENOMEM +There was insufficient memory to create a new anonymous file. +.SH VERSIONS +to-be-defined +.SH CONFORMING TO +.BR memfd_create () +is Linux-specific. +.SH SEE ALSO +.BR shmget (2), +.BR fcntl (2), -- cgit v1.2.3