find: use sysconf(_SC_ARG_MAX) to determine the command-line size limit

The find utility uses a hardcoded value of 32 * 1024 as the limit of
the command-line length when calling 'find -exec ... {} +'. This results
in over 4 times more execve() calls than in coreutils' find.

This patch uses the limit defined in system headers.

Based on the patch by  Bartosz Golaszewski <bartekgola@gmail.com>.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2 files changed, 13 insertions, 17 deletions

diff --git a/findutils/find.c b/findutils/find.c
index 493f72e61..56a7ed3ab 100644
--- a/findutils/find.c
+++ b/findutils/find.c
@@ -419,6 +419,7 @@ struct globals {
         smallint need_print;
         smallint xdev_on;
         recurse_flags_t recurse_flags;
+        IF_FEATURE_FIND_EXEC_PLUS(unsigned max_argv_len;)
 } FIX_ALIASING;
 #define G (*(struct globals*)&bb_common_bufsiz1)
 #define INIT_G() do { \
@@ -428,6 +429,7 @@ struct globals {
         /* we have to zero it out because of NOEXEC */ \
         memset(&G, 0, sizeof(G)); \
         IF_FEATURE_FIND_MAXDEPTH(G.minmaxdepth[1] = INT_MAX;) \
+        IF_FEATURE_FIND_EXEC_PLUS(G.max_argv_len = bb_arg_max() - 2048;) \
         G.need_print = 1; \
         G.recurse_flags = ACTION_RECURSE; \
 } while (0)
@@ -677,7 +679,7 @@ ACTF(exec)
                 ap->file_len += strlen(fileName) + sizeof(char*) + 1;
                 /* If we have lots of files already, exec the command */
                 rc = 1;
-                if (ap->file_len >= 32*1024)
+                if (ap->file_len >= G.max_argv_len)
                         rc = do_exec(ap, NULL);
                 return rc;
         }
diff --git a/findutils/xargs.c b/findutils/xargs.c
index 0ba5b566d..76c4747fe 100644
--- a/findutils/xargs.c
+++ b/findutils/xargs.c
@@ -523,12 +523,7 @@ int xargs_main(int argc, char **argv)
                 argc++;
         }
 
-        /* -s NUM default. fileutils-4.4.2 uses 128k, but I heasitate
-         * to use such a big value - first need to change code to use
-         * growable buffer instead of fixed one.
-         */
-        n_max_chars = 32 * 1024;
-        /* Make smaller if system does not allow our default value.
+        /*
          * The Open Group Base Specifications Issue 6:
          * "The xargs utility shall limit the command line length such that
          * when the command line is invoked, the combined argument
@@ -536,16 +531,15 @@ int xargs_main(int argc, char **argv)
          * in the System Interfaces volume of IEEE Std 1003.1-2001)
          * shall not exceed {ARG_MAX}-2048 bytes".
          */
-        {
-                long arg_max = 0;
-#if defined _SC_ARG_MAX
-                arg_max = sysconf(_SC_ARG_MAX) - 2048;
-#elif defined ARG_MAX
-                arg_max = ARG_MAX - 2048;
-#endif
-                if (arg_max > 0 && n_max_chars > arg_max)
-                        n_max_chars = arg_max;
-        }
+        n_max_chars = bb_arg_max();
+        if (n_max_chars > 32 * 1024)
+                n_max_chars = 32 * 1024;
+        /*
+         * POSIX suggests substracting 2048 bytes from sysconf(_SC_ARG_MAX)
+         * so that the process may safely modify its environment.
+         */
+        n_max_chars -= 2048;
+
         if (opt & OPT_UPTO_SIZE) {
                 n_max_chars = xatou_range(max_chars, 1, INT_MAX);
         }