[PATCH 1/2] find: use sysconf(_SC_ARG_MAX) to determine the command-line size limit
Bartosz Golaszewski
bartekgola at gmail.com
Wed Jun 18 20:11:16 UTC 2014
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 proposes to use the limit defined in system headers.
function old new delta
bb_sc_arg_max - 16 +16
find_main 480 492 +12
func_exec 152 156 +4
xargs_main 923 909 -14
------------------------------------------------------------------------------
(add/remove: 2/0 grow/shrink: 2/1 up/down: 32/-14) Total: 18 bytes
text data bss dec hex filename
815849 4123 9504 829476 ca824 busybox_old
815867 4123 9504 829494 ca836 busybox_unstripped
Signed-off-by: Bartosz Golaszewski <bartekgola at gmail.com>
---
findutils/find.c | 4 +++-
findutils/xargs.c | 23 ++++++++---------------
include/libbb.h | 3 +++
libbb/Kbuild.src | 1 +
libbb/sysconf.c | 30 ++++++++++++++++++++++++++++++
5 files changed, 45 insertions(+), 16 deletions(-)
create mode 100644 libbb/sysconf.c
diff --git a/findutils/find.c b/findutils/find.c
index 8ac3da7..6ffcbab 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(long 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_sc_arg_max();) \
G.need_print = 1; \
G.recurse_flags = ACTION_RECURSE; \
} while (0)
@@ -672,7 +674,7 @@ ACTF(exec)
int rc = 0;
/* If we have lots of files already, exec the command */
- if (ap->file_len >= 32*1024)
+ if (ap->file_len >= G.max_argv_len)
rc = do_exec(ap, NULL);
ap->file_len += strlen(fileName) + sizeof(char*) + 1;
diff --git a/findutils/xargs.c b/findutils/xargs.c
index 0ba5b56..67e7a66 100644
--- a/findutils/xargs.c
+++ b/findutils/xargs.c
@@ -523,11 +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;
+ n_max_chars = bb_sc_arg_max(); /* previously hardcoded to 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
@@ -536,16 +532,13 @@ 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;
- }
+
+ /* TODO Introduce a growable buffer and use bb_sc_arg_max() to
+ * determine a safe value for n_max_chars. Remove this check afterwards.
+ */
+ if (n_max_chars > (32 * 1024))
+ n_max_chars = 32 * 1024;
+
if (opt & OPT_UPTO_SIZE) {
n_max_chars = xatou_range(max_chars, 1, INT_MAX);
}
diff --git a/include/libbb.h b/include/libbb.h
index a1a0dc1..3e645d6 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -731,6 +731,9 @@ extern void *xmalloc_open_read_close(const char *filename, size_t *maxsz_p) FAST
/* Never returns NULL */
extern void *xmalloc_xopen_read_close(const char *filename, size_t *maxsz_p) FAST_FUNC RETURNS_MALLOC;
+/* sysconf() wrappers */
+long bb_sc_arg_max(void) FAST_FUNC;
+
#define SEAMLESS_COMPRESSION (0 \
|| ENABLE_FEATURE_SEAMLESS_XZ \
|| ENABLE_FEATURE_SEAMLESS_LZMA \
diff --git a/libbb/Kbuild.src b/libbb/Kbuild.src
index 6578d11..62680bd 100644
--- a/libbb/Kbuild.src
+++ b/libbb/Kbuild.src
@@ -92,6 +92,7 @@ lib-y += skip_whitespace.o
lib-y += speed_table.o
lib-y += str_tolower.o
lib-y += strrstr.o
+lib-y += sysconf.o
lib-y += time.o
lib-y += trim.o
lib-y += u_signal_names.o
diff --git a/libbb/sysconf.c b/libbb/sysconf.c
new file mode 100644
index 0000000..3635c43
--- /dev/null
+++ b/libbb/sysconf.c
@@ -0,0 +1,30 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * Various system configuration helpers.
+ *
+ * Copyright (C) 2014 Bartosz Golaszewski <bartekgola at gmail.com>
+ *
+ * Licensed under GPLv2 or later, see file LICENSE in this source tree.
+ */
+
+#include "libbb.h"
+
+/*
+ * Return the maximum command line length.
+ *
+ * In case neither _SC_ARG_MAX nor ARG_MAX macros are defined
+ * we resort to using a small (ie. safe) default of 32 * 1024.
+ *
+ * POSIX suggests to substract 2048 bytes from sysconf(_SC_ARG_MAX)
+ * so that the process may safely modify its environment.
+ */
+long FAST_FUNC bb_sc_arg_max(void)
+{
+#if defined _SC_ARG_MAX
+ return sysconf(_SC_ARG_MAX) - 2048;
+#elif defined ARG_MAX
+ return ARG_MAX - 2048;
+#else
+ return 32 * 1024;
+#endif
+}
--
1.9.1
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