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, 5 deletions

diff --git a/src/shared/logs-show.c b/src/shared/logs-show.c
index af7f8f345e..ffb921e4a8 100644
--- a/src/shared/logs-show.c
+++ b/src/shared/logs-show.c
@@ -1278,11 +1278,10 @@ static int get_boot_id_for_machine(const char *machine, sd_id128_t *boot_id) {
         if (socketpair(AF_UNIX, SOCK_DGRAM, 0, pair) < 0)
                 return -errno;
 
-        child = fork();
-        if (child < 0)
-                return -errno;
-
-        if (child == 0) {
+        r = safe_fork("(sd-bootid)", FORK_RESET_SIGNALS|FORK_DEATHSIG, &child);
+        if (r < 0)
+                return r;
+        if (r == 0) {
                 int fd;
 
                 pair[0] = safe_close(pair[0]);