Initialize command-line-max-length with sysconf(3)

* lisp/subr.el (command-line-max-length): Move from here ...
* src/callproc.c (syms_of_callproc): <Vcommand_line_max_length>:
... to here.  Initialize by calling sysconf(3) if possible.

2 files changed, 14 insertions, 14 deletions

diff --git a/lisp/subr.el b/lisp/subr.el
index b9fbd739a5a..4cae2845d96 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -5089,20 +5089,6 @@ newlines."
                        shell-file-name delete buffer nil
                        shell-command-switch command))
 
-(defvar command-line-max-length
-  ;; Currently we use the same value everywhere.  If we actually use
-  ;; larger values on some systems at some point, then we need to make
-  ;; sure we handle whether the command will be run remotely via TRAMP.
-  ;; FIXME: This value is very small, it might easily all be used up by
-  ;; `process-environment'.  We really want a larger value on POSIX.
-  4096
-  "Maximum length of a command and its arguments on this system.
-This is measured in characters.
-Used by `multiple-command-partition-arguments'.  Other code calls that
-function for cases in which it's known to be safe to run the command
-multiple times on subsequent partitions of the list of arguments.
-(In a shell script, you might use the `xargs' utility.)")
-
 (defun multiple-command-partition-arguments (command arguments &optional shellp)
   "Partition ARGUMENTS of COMMAND to avoid command line length limits.
 This function is for running commands on each element of ARGUMENTS where
diff --git a/src/callproc.c b/src/callproc.c
index 51b5a1c4074..abb944c3aad 100644
--- a/src/callproc.c
+++ b/src/callproc.c
@@ -2237,6 +2237,20 @@ the system.  */);
   Vrcs2log_program_name = build_string ("librcs2log.so");
 #endif /* !HAVE_ANDROID || ANDROID_STUBIFY */
 
+  DEFVAR_LISP ("command-line-max-length", Vcommand_line_max_length,
+    doc: /* Maximum length of a command and its arguments on this system.
+This is measured in characters.
+Used by `multiple-command-partition-arguments'.  Other code calls that
+function for cases in which it's known to be safe to run the command
+multiple times on subsequent partitions of the list of arguments.
+(In a shell script, you might use the `xargs' utility.)  */);
+#if defined _SC_ARG_MAX
+  /* Divide it by 4 as a crude way to go bytes->characters.  */
+  Vcommand_line_max_length = make_fixnum (sysconf (_SC_ARG_MAX) / 4);
+#else  /* defined _SC_ARG_MAX */
+  Vcommand_line_max_length = make_fixnum (4096);
+#endif  /* defined _SC_ARG_MAX */
+
   defsubr (&Scall_process);
   defsubr (&Sgetenv_internal);
   defsubr (&Scall_process_region);