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/*
* Copyright (C) 2005-2009 Junjiro Okajima
*
* This program, aufs 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 program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
/* cf. fstab.c or the locking for /etc/mtab in util-linux */
/*
* we need to extract a part of util-linux and create a simple and generic
* library for locking /etc/mtab.
*/
/* #include <linux/proc_fs.h> */
#define PROC_SUPER_MAGIC 0x9fa0
#include <sys/stat.h>
#include <sys/statfs.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <mntent.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include "au_util.h"
void au_print_ent(struct mntent *ent)
{
printf("%s on %s type %s (%s)\n",
ent->mnt_fsname, ent->mnt_dir, ent->mnt_type, ent->mnt_opts);
}
/* ---------------------------------------------------------------------- */
static void lock_mtab(char *pid_file)
{
int err, i;
for (i = 0; i < 5; i++) {
err = link(pid_file, MTab "~");
if (!err)
break;
sleep(1);
}
if (err)
AuFin(MTab "~");
}
static void unlock_mtab(void)
{
int err;
err = rename(MTab "~", MTab);
if (err)
AuFin(MTab);
}
static void append_mtab(FILE *fp, FILE *ofp, struct mntent *ent)
{
int err;
struct mntent *p;
while ((p = getmntent(ofp))) {
err = addmntent(fp, p);
if (err)
AuFin("addmntent");
}
err = addmntent(fp, ent);
if (err)
AuFin("addmntent");
}
/* todo: there are some cases which options are not changed */
static void update_mtab(FILE *fp, char *mntpnt, int do_remount, int do_verbose)
{
int err;
long pos;
FILE *ofp;
struct mntent ent, *p;
/* prohibit updating mount options for this mntpnt */
au_plink_maint(mntpnt);
err = au_proc_getmntent(mntpnt, &ent);
if (err)
AuFin("no such mount point");
ofp = setmntent(MTab, "r");
if (!ofp)
AuFin(MTab);
if (do_remount) {
/* find the last one */
pos = -1;
while ((p = getmntent(ofp))) {
if (!strcmp(p->mnt_dir, mntpnt))
pos = ftell(ofp);
}
rewind(ofp);
if (pos > 0) {
while ((p = getmntent(ofp))) {
if (ftell(ofp) == pos) {
/* replace the line */
p = &ent;
pos = -1;
}
err = addmntent(fp, p);
if (err)
AuFin("addmntent");
}
if (pos > 0)
AuFin("internal error");
} else
append_mtab(fp, ofp, &ent);
} else
append_mtab(fp, ofp, &ent);
endmntent(ofp); /* ignore */
au_plink_maint(NULL);
if (do_verbose)
au_print_ent(&ent);
}
/* ---------------------------------------------------------------------- */
int au_update_mtab(char *mntpnt, int do_remount, int do_verbose)
{
int err, fd, status, e2;
pid_t pid;
ino_t ino;
struct stat st;
struct statfs stfs;
struct flock flock = {
.l_type = F_WRLCK,
.l_whence = SEEK_SET,
.l_start = 0,
.l_len = 0
};
char pid_file[sizeof(MTab "~.") + 20];
FILE *fp;
err = statfs(MTab, &stfs);
if (stfs.f_type == PROC_SUPER_MAGIC)
return 0;
snprintf(pid_file, sizeof(pid_file), MTab "~.%d", getpid());
fd = open(pid_file, O_RDWR | O_CREAT | O_EXCL,
S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
if (fd < 0)
AuFin("%s", pid_file);
err = fcntl(fd, F_SETLK, &flock);
if (err)
AuFin("%s", pid_file);
fp = fdopen(fd, "r+");
if (!fp)
AuFin("%s", pid_file);
pid = fork();
if (!pid) {
lock_mtab(pid_file);
update_mtab(fp, mntpnt, do_remount, do_verbose);
unlock_mtab();
return 0;
} else if (pid < 0)
AuFin("fork");
err = fstat(fd, &st);
if (err)
perror(pid_file);
ino = st.st_ino;
err = waitpid(pid, &status, 0);
if (err < 0) {
perror(pid_file);
goto out;
}
err = !WIFEXITED(status);
if (!err)
err = WEXITSTATUS(status);
e2 = unlink(pid_file);
if (e2 && errno != ENOENT)
perror(pid_file);
e2 = stat(MTab "~", &st);
if (!e2) {
if (st.st_ino == ino) {
/*
* The inode number is same,
* it means it is we who made the file.
* If someone else removed our file between stat(2) and
* unlink(2), it is a breakage of the rule.
*/
e2 = unlink(MTab "~");
if (e2)
perror(MTab);
}
} else if (errno != ENOENT)
perror(MTab "~");
fclose(fp);
out:
return err;
}
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