Merge pull request #7915 from poettering/pids-max-tweak

src/basic/process-util.h

@@ -184,3 +184,22 @@ static inline int safe_fork(const char *name, ForkFlags flags, pid_t *ret_pid) {
 }
 
 int fork_agent(const char *name, const int except[], unsigned n_except, pid_t *pid, const char *path, ...);
+
+#if SIZEOF_PID_T == 4
+/* The highest possibly (theoretic) pid_t value on this architecture. */
+#define PID_T_MAX ((pid_t) INT32_MAX)
+/* The maximum number of concurrent processes Linux allows on this architecture, as well as the highest valid PID value
+ * the kernel will potentially assign. This reflects a value compiled into the kernel (PID_MAX_LIMIT), and sets the
+ * upper boundary on what may be written to the /proc/sys/kernel/pid_max sysctl (but do note that the sysctl is off by
+ * 1, since PID 0 can never exist and there can hence only be one process less than the limit would suggest). Since
+ * these values are documented in proc(5) we feel quite confident that they are stable enough for the near future at
+ * least to define them here too. */
+#define TASKS_MAX 4194303U
+#elif SIZEOF_PID_T == 2
+#define PID_T_MAX ((pid_t) INT16_MAX)
+#define TASKS_MAX 32767U
+#else
+#error "Unknown pid_t size"
+#endif
+
+assert_cc(TASKS_MAX <= (unsigned long) PID_T_MAX)