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/machine/machined-dbus.c b/src/machine/machined-dbus.c
index 330d6b3d6e..c5e59c4716 100644
--- a/src/machine/machined-dbus.c
+++ b/src/machine/machined-dbus.c
@@ -1078,11 +1078,10 @@ static int method_clean_pool(sd_bus_message *message, void *userdata, sd_bus_err
                 return -errno;
 
         /* This might be a slow operation, run it asynchronously in a background process */
-        child = fork();
-        if (child < 0)
-                return sd_bus_error_set_errnof(error, errno, "Failed to fork(): %m");
-
-        if (child == 0) {
+        r = safe_fork("(sd-clean)", FORK_RESET_SIGNALS, &child);
+        if (r < 0)
+                return sd_bus_error_set_errnof(error, r, "Failed to fork(): %m");
+        if (r == 0) {
                 _cleanup_(image_hashmap_freep) Hashmap *images = NULL;
                 bool success = true;
                 Image *image;