rm: improve efficiency of rm -r (without -f) from O(N^2) to O(N)

where N is the depth of the deepest hierarchy rm is processing.
* src/remove.c (write_protected_non_symlink): Use faccessat to
avoid O(N)-per-entry cost of calling euidaccess.
* m4/jm-macros.m4 (coreutils_MACROS): Check for faccessat.

diff --git a/m4/jm-macros.m4 b/m4/jm-macros.m4
index f4d43f1dda5c6756d51f9c21c1b524d8a461a9c0..75ee75e2d3616b18451e309057574f492f14f1aa 100644 (file)
--- a/m4/jm-macros.m4
+++ b/m4/jm-macros.m4
@@ -92,6 +92,9 @@ AC_DEFUN([coreutils_MACROS],
   # for cp.c
   AC_CHECK_FUNCS_ONCE([utimensat])
 
+  # for remove.c
+  AC_CHECK_FUNCS_ONCE([faccessat])
+
   dnl This can't use AC_REQUIRE; I'm not quite sure why.
   cu_PREREQ_STAT_PROG
 

diff --git a/src/remove.c b/src/remove.c
index 32f67a1816e0dcaacb5a55aea6a10d2a0ed917a8..2db38590921c4b98586b7d7668d6355a1302d35a 100644 (file)
--- a/src/remove.c
+++ b/src/remove.c
@@ -172,6 +172,13 @@ write_protected_non_symlink (int fd_cwd,
         mess up with long file names). */
 
   {
+    /* Use faccessat if possible, so as to avoid the expense
+       of processing an N-component name.  */
+#if HAVE_FACCESSAT && AT_EACCESS
+    if (faccessat (fd_cwd, file, W_OK, AT_EACCESS) == 0)
+      return 0;
+#endif
+
     /* This implements #5: */
     size_t file_name_len = strlen (full_name);