shutdown: complain if process excluded from killing spree runs of the same rootfs as PID1

src/basic/process-util.c

@@ -48,6 +48,7 @@
 #include "missing.h"
 #include "process-util.h"
 #include "signal-util.h"
+#include "stat-util.h"
 #include "string-table.h"
 #include "string-util.h"
 #include "user-util.h"
@@ -637,6 +638,17 @@ bool pid_is_alive(pid_t pid) {
         return true;
 }
 
+int pid_from_same_root_fs(pid_t pid) {
+        const char *root;
+
+        if (pid < 0)
+                return 0;
+
+        root = procfs_file_alloca(pid, "root");
+
+        return files_same(root, "/proc/1/root");
+}
+
 bool is_main_thread(void) {
         static thread_local int cached = 0;
 

src/basic/process-util.h

@@ -70,6 +70,7 @@ int getenv_for_pid(pid_t pid, const char *field, char **_value);
 
 bool pid_is_alive(pid_t pid);
 bool pid_is_unwaited(pid_t pid);
+int pid_from_same_root_fs(pid_t pid);
 
 bool is_main_thread(void);