anon_file.c 3.74 KB
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/*
 * Copyright © 2012 Collabora, Ltd.
 *
 * Permission is hereby granted, free of charge, to any person obtaining
 * a copy of this software and associated documentation files (the
 * "Software"), to deal in the Software without restriction, including
 * without limitation the rights to use, copy, modify, merge, publish,
 * distribute, sublicense, and/or sell copies of the Software, and to
 * permit persons to whom the Software is furnished to do so, subject to
 * the following conditions:
 *
 * The above copyright notice and this permission notice (including the
 * next paragraph) shall be included in all copies or substantial
 * portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
 * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
 * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
 * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

/*
 * Based on weston shared/os-compatibility.c
 */

#ifndef WIN32
#include "anon_file.h"

#include <unistd.h>
#include <fcntl.h>
#include <errno.h>

#ifdef __FreeBSD__
#include <sys/mman.h>
#elif defined(HAVE_MEMFD_CREATE)
#include <sys/syscall.h>
#include <linux/memfd.h>
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#else
#include <stdio.h>
#include <stdlib.h>
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#endif

#if !(defined(__FreeBSD__) || defined(HAVE_MEMFD_CREATE) || defined(HAVE_MKOSTEMP))
static int
set_cloexec_or_close(int fd)
{
   long flags;

   if (fd == -1)
      return -1;

   flags = fcntl(fd, F_GETFD);
   if (flags == -1)
      goto err;

   if (fcntl(fd, F_SETFD, flags | FD_CLOEXEC) == -1)
      goto err;

   return fd;

err:
   close(fd);
   return -1;
}
#endif

#if !(defined(__FreeBSD__) || defined(HAVE_MEMFD_CREATE))
static int
create_tmpfile_cloexec(char *tmpname)
{
   int fd;

#ifdef HAVE_MKOSTEMP
   fd = mkostemp(tmpname, O_CLOEXEC);
#else
   fd = mkstemp(tmpname);
#endif

   if (fd < 0) {
      return fd;
   }

#ifndef HAVE_MKOSTEMP
   fd = set_cloexec_or_close(fd);
#endif

   unlink(tmpname);
   return fd;
}
#endif

/*
 * Create a new, unique, anonymous file of the given size, and
 * return the file descriptor for it. The file descriptor is set
 * CLOEXEC. The file is immediately suitable for mmap()'ing
 * the given size at offset zero.
 *
 * An optional name for debugging can be provided as the second argument.
 *
 * The file should not have a permanent backing store like a disk,
 * but may have if XDG_RUNTIME_DIR is not properly implemented in OS.
 *
 * If memfd or SHM_ANON is supported, the filesystem is not touched at all.
 * Otherwise, the file name is deleted from the file system.
 *
 * The file is suitable for buffer sharing between processes by
 * transmitting the file descriptor over Unix sockets using the
 * SCM_RIGHTS methods.
 */
int
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os_create_anonymous_file(off_t size, const char *debug_name)
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{
   int fd, ret;
#ifdef __FreeBSD__
   (void*)debug_name;
   fd = shm_open(SHM_ANON, O_CREAT | O_RDWR | O_CLOEXEC, 0600);
#elif defined(HAVE_MEMFD_CREATE)
   if (!debug_name)
      debug_name = "mesa-shared";
   fd = syscall(SYS_memfd_create, debug_name, MFD_CLOEXEC);
#else
   const char *path;
   char *name;

   path = getenv("XDG_RUNTIME_DIR");
   if (!path) {
      errno = ENOENT;
      return -1;
   }

   if (debug_name)
      asprintf(&name, "%s/mesa-shared-%s-XXXXXX", path, debug_name);
   else
      asprintf(&name, "%s/mesa-shared-XXXXXX", path);
   if (!name)
      return -1;

   fd = create_tmpfile_cloexec(name);

   free(name);
#endif

   if (fd < 0)
      return -1;

   ret = ftruncate(fd, size);
   if (ret < 0) {
      close(fd);
      return -1;
   }

   return fd;
}
#endif