tree-wide: introduce new safe_fork() helper and port everything over

This adds a new safe_fork() wrapper around fork() and makes use of it
everywhere. The new wrapper does a couple of things we previously did
manually and separately in a safer, more correct and automatic way:

1. Optionally resets signal handlers/mask in the child

2. Sets a name on all processes we fork off right after forking off (and
   the patch assigns useful names for all processes we fork off now,
   following a systematic naming scheme: always enclosed in () – in order
   to indicate that these are not proper, exec()ed processes, but only
   forked off children, and if the process is long-running with only our
   own code, without execve()'ing something else, it gets am "sd-" prefix.)

3. Optionally closes all file descriptors in the child

4. Optionally sets a PR_SET_DEATHSIG to SIGTERM in the child, in a safe
   way so that the parent dying before this happens being handled
   safely.

5. Optionally reopens the logs

6. Optionally connects stdin/stdout/stderr to /dev/null

7. Debug logs about the forked off processes.

1 files changed, 4 insertions, 9 deletions

diff --git a/src/remount-fs/remount-fs.c b/src/remount-fs/remount-fs.c
index 2d7cf723f4..1f0397cf6f 100644
--- a/src/remount-fs/remount-fs.c
+++ b/src/remount-fs/remount-fs.c
@@ -87,19 +87,14 @@ int main(int argc, char *argv[]) {
 
                 log_debug("Remounting %s", me->mnt_dir);
 
-                pid = fork();
-                if (pid < 0) {
-                        r = log_error_errno(errno, "Failed to fork: %m");
+                r = safe_fork("(remount)", FORK_RESET_SIGNALS|FORK_DEATHSIG, &pid);
+                if (r < 0) {
+                        log_error_errno(r, "Failed to fork: %m");
                         goto finish;
                 }
-
-                if (pid == 0) {
+                if (r == 0) {
                         /* Child */
 
-                        (void) reset_all_signal_handlers();
-                        (void) reset_signal_mask();
-                        (void) prctl(PR_SET_PDEATHSIG, SIGTERM);
-
                         execv(MOUNT_PATH, STRV_MAKE(MOUNT_PATH, me->mnt_dir, "-o", "remount"));
 
                         log_error_errno(errno, "Failed to execute " MOUNT_PATH ": %m");