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remount-fs: optionally remount / writable, if we are told through an env var

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This commit is contained in:
Lennart Poettering 2018-11-23 19:47:41 +01:00
parent 58b86fdf1d
commit 59f13dd6f8
2 changed files with 63 additions and 25 deletions
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8
docs/ENVIRONMENT.md
View File

@ -165,3 +165,11 @@ systemd itself:
* `$SYSTEMD_ACTIVATION_SCOPE` — closely related to `$SYSTEMD_ACTIVATION_UNIT`,
it is either set to `system` or `user` depending on whether the NSS/PAM
module is called by systemd in `--system` or `--user` mode.
systemd-remount-fs:
* `$SYSTEMD_REMOUNT_ROOT_RW=1` — if set and and no entry for the root directory
exists in /etc/fstab (this file always takes precedence), then the root
directory is remounted writable. This is primarily used by
systemd-gpt-auto-generator to ensure the root partition is mounted writable
in accordance to the GPT partition flags.

80
src/remount-fs/remount-fs.c
View File

@ -8,6 +8,7 @@
#include <sys/wait.h>
#include <unistd.h>
#include "env-util.h"
#include "exit-status.h"
#include "log.h"
#include "main-func.h"
@ -49,6 +50,7 @@ static int track_pid(Hashmap **h, const char *path, pid_t pid) {
static int run(int argc, char *argv[]) {
_cleanup_hashmap_free_free_ Hashmap *pids = NULL;
_cleanup_endmntent_ FILE *f = NULL;
bool has_root = false;
struct mntent* me;
int r;
@ -62,44 +64,72 @@ static int run(int argc, char *argv[]) {
f = setmntent("/etc/fstab", "re");
if (!f) {
if (errno == ENOENT)
return 0;
if (errno != ENOENT)
return log_error_errno(errno, "Failed to open /etc/fstab: %m");
} else {
while ((me = getmntent(f))) {
pid_t pid;
return log_error_errno(errno, "Failed to open /etc/fstab: %m");
/* Remount the root fs, /usr and all API VFS */
if (!mount_point_is_api(me->mnt_dir) &&
!PATH_IN_SET(me->mnt_dir, "/", "/usr"))
continue;
log_debug("Remounting %s...", me->mnt_dir);
if (path_equal(me->mnt_dir, "/"))
has_root = true;
r = safe_fork("(remount)", FORK_RESET_SIGNALS|FORK_DEATHSIG|FORK_RLIMIT_NOFILE_SAFE|FORK_LOG, &pid);
if (r < 0)
return r;
if (r == 0) {
/* Child */
execv(MOUNT_PATH, STRV_MAKE(MOUNT_PATH, me->mnt_dir, "-o", "remount"));
log_error_errno(errno, "Failed to execute " MOUNT_PATH ": %m");
_exit(EXIT_FAILURE);
}
/* Parent */
r = track_pid(&pids, me->mnt_dir, pid);
if (r < 0)
return r;
}
}
while ((me = getmntent(f))) {
pid_t pid;
if (!has_root) {
/* The $SYSTEMD_REMOUNT_ROOT_RW environment variable is set by systemd-gpt-auto-generator to tell us
* whether to remount things. We honour it only if there's no explicit line in /etc/fstab configured
* which takes precedence. */
/* Remount the root fs, /usr and all API VFS */
if (!mount_point_is_api(me->mnt_dir) &&
!PATH_IN_SET(me->mnt_dir, "/", "/usr"))
continue;
r = getenv_bool("SYSTEMD_REMOUNT_ROOT_RW");
if (r > 0) {
pid_t pid;
log_debug("Remounting %s", me->mnt_dir);
log_debug("Remounting / writable...");
r = safe_fork("(remount)", FORK_RESET_SIGNALS|FORK_DEATHSIG|FORK_RLIMIT_NOFILE_SAFE|FORK_LOG, &pid);
if (r < 0)
return r;
if (r == 0) {
/* Child */
r = safe_fork("(remount-rw)", FORK_RESET_SIGNALS|FORK_DEATHSIG|FORK_LOG, &pid);
if (r < 0)
return r;
if (r == 0) {
/* Child */
execv(MOUNT_PATH, STRV_MAKE(MOUNT_PATH, "/", "-o", "remount,rw"));
log_error_errno(errno, "Failed to execute " MOUNT_PATH ": %m");
_exit(EXIT_FAILURE);
}
execv(MOUNT_PATH, STRV_MAKE(MOUNT_PATH, me->mnt_dir, "-o", "remount"));
r = track_pid(&pids, "/", pid);
if (r < 0)
return r;
log_error_errno(errno, "Failed to execute " MOUNT_PATH ": %m");
_exit(EXIT_FAILURE);
}
/* Parent */
r = track_pid(&pids, me->mnt_dir, pid);
if (r < 0)
return r;
} else if (r < 0 && r != -ENXIO)
log_warning_errno(r, "Failed to parse $SYSTEMD_REMOUNT_ROOT_RW, ignoring: %m");
}
r = 0;
while (!hashmap_isempty(pids)) {
siginfo_t si = {};
_cleanup_free_ char *s = NULL;
siginfo_t si = {};
if (waitid(P_ALL, 0, &si, WEXITED) < 0) {
if (errno == EINTR)