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, 6 insertions, 22 deletions

diff --git a/src/journal-remote/journal-remote.c b/src/journal-remote/journal-remote.c
index e44989e1ba..32416493fd 100644
--- a/src/journal-remote/journal-remote.c
+++ b/src/journal-remote/journal-remote.c
@@ -81,27 +81,20 @@ static bool arg_trust_all = false;
  **********************************************************************/
 
 static int spawn_child(const char* child, char** argv) {
-        int fd[2];
-        pid_t parent_pid, child_pid;
-        int r;
+        pid_t child_pid;
+        int fd[2], r;
 
         if (pipe(fd) < 0)
                 return log_error_errno(errno, "Failed to create pager pipe: %m");
 
-        parent_pid = getpid_cached();
-
-        child_pid = fork();
-        if (child_pid < 0) {
-                r = log_error_errno(errno, "Failed to fork: %m");
+        r = safe_fork("(remote)", FORK_RESET_SIGNALS|FORK_DEATHSIG, &child_pid);
+        if (r < 0) {
                 safe_close_pair(fd);
-                return r;
+                return log_error_errno(r, "Failed to fork: %m");
         }
 
         /* In the child */
-        if (child_pid == 0) {
-
-                (void) reset_all_signal_handlers();
-                (void) reset_signal_mask();
+        if (r == 0) {
 
                 r = dup2(fd[1], STDOUT_FILENO);
                 if (r < 0) {
@@ -111,15 +104,6 @@ static int spawn_child(const char* child, char** argv) {
 
                 safe_close_pair(fd);
 
-                /* Make sure the child goes away when the parent dies */
-                if (prctl(PR_SET_PDEATHSIG, SIGTERM) < 0)
-                        _exit(EXIT_FAILURE);
-
-                /* Check whether our parent died before we were able
-                 * to set the death signal */
-                if (getppid() != parent_pid)
-                        _exit(EXIT_SUCCESS);
-
                 execvp(child, argv);
                 log_error_errno(errno, "Failed to exec child %s: %m", child);
                 _exit(EXIT_FAILURE);