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/*
* Copyright © 2010 Codethink Limited
* Copyright © 2012 Canonical Limited
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the licence, or (at your option) any later version.
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*
* Author: Ryan Lortie <desrt@desrt.ca>
*/
#include "config.h"
#include "dconf-shm.h"
#include <sys/mman.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
static gchar *
dconf_shm_get_shmdir (void)
{
static gchar *shmdir;
if (g_once_init_enter (&shmdir))
g_once_init_leave (&shmdir, g_build_filename (g_get_user_runtime_dir (), "dconf", NULL));
return shmdir;
}
void
dconf_shm_close (guint8 *shm)
{
if (shm)
munmap (shm, 1);
}
guint8 *
dconf_shm_open (const gchar *name)
{
const gchar *shmdir;
gchar *filename;
void *memory;
gint fd;
shmdir = dconf_shm_get_shmdir ();
filename = g_build_filename (shmdir, name, NULL);
memory = NULL;
fd = -1;
if (g_mkdir_with_parents (shmdir, 0700) != 0)
{
g_critical ("unable to create directory '%s': %s. dconf will not work properly.", shmdir, g_strerror (errno));
goto out;
}
fd = open (filename, O_RDWR | O_CREAT, 0600);
if (fd == -1)
{
g_critical ("unable to create file '%s': %s. dconf will not work properly.", filename, g_strerror (errno));
goto out;
}
/* ftruncate(fd, 1) is not sufficient because it does not actually
* ensure that the space is available (which could give a SIGBUS
* later).
*
* posix_fallocate() is also problematic because it is implemented in
* a racy way in the libc if unavailable for a particular filesystem
* (as is the case for tmpfs, which is where we probably are).
*
* By writing to the second byte in the file we ensure we don't
* overwrite the first byte (which is the one we care about).
*/
if (pwrite (fd, "", 1, 1) != 1)
{
g_critical ("failed to allocate file '%s': %s. dconf will not work properly.", filename, g_strerror (errno));
goto out;
}
memory = mmap (NULL, 1, PROT_READ, MAP_SHARED, fd, 0);
g_assert (memory != MAP_FAILED);
g_assert (memory != NULL);
out:
g_free (filename);
close (fd);
return memory;
}
void
dconf_shm_flag (const gchar *name)
{
const gchar *shmdir;
gchar *filename;
gint fd;
shmdir = dconf_shm_get_shmdir ();
filename = g_build_filename (shmdir, name, NULL);
/* We need O_RDWR for PROT_WRITE.
*
* This is probably due to the fact that some architectures can't make
* write-only mappings (so they end up being readable as well).
*/
fd = open (filename, O_RDWR);
if (fd >= 0)
{
/* In theory we could have opened the file after a client created
* it but before they called pwrite(). Do the pwrite() ourselves
* to make sure (so we don't get SIGBUS in a moment).
*
* If this fails then it will probably fail for the client too.
* If it doesn't then there's not really much we can do...
*/
if (pwrite (fd, "", 1, 1) == 1)
{
guint8 *shm;
/* It would have been easier for us to do write(fd, "\1", 1);
* but this causes problems on kernels (ie: OpenBSD) that
* don't sync up their filesystem cache with mmap()ed regions.
*
* Using mmap() works everywhere.
*
* See https://bugzilla.gnome.org/show_bug.cgi?id=687334 about
* why we need to have PROT_READ even though we only write.
*/
shm = mmap (NULL, 1, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
g_assert (shm != MAP_FAILED);
*shm = 1;
munmap (shm, 1);
}
close (fd);
unlink (filename);
}
g_free (filename);
}
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