/*      $NetBSD: shm.c,v 1.3 2015/07/08 07:14:38 martin Exp $   */

/*-
* Copyright (c) 2013 The NetBSD Foundation, Inc.
* All rights reserved.
*
* This code is derived from software contributed to The NetBSD Foundation
* by Mindaugas Rasiukevicius.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
*    notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
*    notice, this list of conditions and the following disclaimer in the
*    documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
* ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
* TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
* BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*/

/*
* Interface for POSIX shared memory objects.
*/

#include <sys/cdefs.h>
__RCSID("$NetBSD: shm.c,v 1.3 2015/07/08 07:14:38 martin Exp $");

#include <sys/mman.h>
#include <sys/mount.h>
#include <sys/stat.h>

#include <stdio.h>
#include <stdbool.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <limits.h>

/*
* Shared memory objects are supported using tmpfs.
*/
#define SHMFS_DIR_PATH          "/var/shm"
#define SHMFS_DIR_MODE          (S_ISVTX | S_IRWXU | S_IRWXG | S_IRWXO)
#define SHMFS_OBJ_PREFIX        ".shmobj_"

#define MOUNT_SHMFS             MOUNT_TMPFS

static bool                     shm_ok = false;

static bool
_shm_check_fs(void)
{
       int fd;
       struct statvfs sv;
       struct stat st;

       fd = open(SHMFS_DIR_PATH, O_DIRECTORY|O_RDONLY);
       if (fd == -1)
               return false;

       if (fstatvfs1(fd, &sv, ST_NOWAIT) == -1)
               goto out;

       if (strncmp(sv.f_fstypename, MOUNT_SHMFS, sizeof(sv.f_fstypename)))
               goto out;

       if (fstat(fd, &st) == -1)
               goto out;

       if ((st.st_mode & SHMFS_DIR_MODE) != SHMFS_DIR_MODE)
               goto out;

       shm_ok = true;

out:
       close(fd);
       return shm_ok;
}

static bool
_shm_get_path(char *buf, size_t len, const char *name)
{
       int ret;

       if (__predict_false(!shm_ok) && !_shm_check_fs()) {
               errno = ENOTSUP;
               return false;
       }

       /*
        * As per POSIX: the name should begin with a slash character.
        * We may disallow other slashes (implementation-defined behaviour).
        */
       if (*name++ != '/' || strchr(name, '/') != NULL) {
               errno = EINVAL;
               return false;
       }

       ret = snprintf(buf, len, SHMFS_DIR_PATH "/" SHMFS_OBJ_PREFIX "%s",
           name);

       if ((size_t)ret >= len) {
               errno = ENAMETOOLONG;
               return false;
       }
       return ret != -1;
}

int
shm_open(const char *name, int oflag, mode_t mode)
{
       char path[PATH_MAX];

       if (!_shm_get_path(path, sizeof(path), name)) {
               return -1;
       }
       return open(path, oflag | O_CLOEXEC | O_NOFOLLOW, mode);
}

int
shm_unlink(const char *name)
{
       char path[PATH_MAX];

       if (!_shm_get_path(path, sizeof(path), name)) {
               return -1;
       }
       return unlink(path);
}