Introduce sc_arg_max() helper

Just a cast and an assert.

src/basic/env-util.c

@@ -72,7 +72,7 @@ bool env_value_is_valid(const char *e) {
          * either. Discounting the shortest possible variable name of
          * length 1, the equal sign and trailing NUL this hence leaves
          * ARG_MAX-3 as longest possible variable value. */
-        if (strlen(e) > (size_t) sysconf(_SC_ARG_MAX) - 3)
+        if (strlen(e) > sc_arg_max() - 3)
                 return false;
 
         return true;
@@ -95,7 +95,7 @@ bool env_assignment_is_valid(const char *e) {
          * be > ARG_MAX, hence the individual variable assignments
          * cannot be either, but let's leave room for one trailing NUL
          * byte. */
-        if (strlen(e) > (size_t) sysconf(_SC_ARG_MAX) - 1)
+        if (strlen(e) > sc_arg_max() - 1)
                 return false;
 
         return true;

src/basic/env-util.h

@@ -4,10 +4,17 @@
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdio.h>
+#include <unistd.h>
 
 #include "macro.h"
 #include "string.h"
 
+static inline size_t sc_arg_max(void) {
+        long l = sysconf(_SC_ARG_MAX);
+        assert(l > 0);
+        return (size_t) l;
+}
+
 bool env_name_is_valid(const char *e);
 bool env_value_is_valid(const char *e);
 bool env_assignment_is_valid(const char *e);

src/basic/process-util.c

@@ -25,6 +25,7 @@
 #include "alloc-util.h"
 #include "architecture.h"
 #include "escape.h"
+#include "env-util.h"
 #include "fd-util.h"
 #include "fileio.h"
 #include "fs-util.h"
@@ -126,12 +127,9 @@ int get_process_cmdline(pid_t pid, size_t max_length, bool comm_fallback, char *
         if (r < 0)
                 return r;
 
-        if (max_length == 0) {
+        if (max_length == 0)
                 /* This is supposed to be a safety guard against runaway command lines. */
-                long l = sysconf(_SC_ARG_MAX);
-                assert(l > 0);
-                max_length = l;
-        }
+                max_length = sc_arg_max();
 
         if (max_length == 1) {