Search the userland buffer of dirent structures before falling back to

getdents(2).  No functional change, but considerable speedup in many
cases, see http://marc.info/?l=openbsd-tech&m=138369623117934 for some
approximate numbers.
ok guenther@,  "good diagnosis" deraadt@

2 files changed, 46 insertions, 26 deletions

diff --git a/lib/libc/gen/opendir.c b/lib/libc/gen/opendir.c
index 86038754999..6b9adad9c79 100644
--- a/lib/libc/gen/opendir.c
+++ b/lib/libc/gen/opendir.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: opendir.c,v 1.25 2013/10/06 17:57:11 guenther Exp $ */
+/*	$OpenBSD: opendir.c,v 1.26 2013/11/06 20:35:25 schwarze Exp $ */
 /*
  * Copyright (c) 1983, 1993
  *	The Regents of the University of California.  All rights reserved.
@@ -111,6 +111,7 @@ __fdopendir(int fd)
 		return (NULL);
 	}
 
+	dirp->dd_size = 0;
 	dirp->dd_loc = 0;
 	dirp->dd_fd = fd;
 	dirp->dd_lock = NULL;
diff --git a/lib/libc/gen/seekdir.c b/lib/libc/gen/seekdir.c
index 66c9bbca209..f0523af677c 100644
--- a/lib/libc/gen/seekdir.c
+++ b/lib/libc/gen/seekdir.c
@@ -1,31 +1,18 @@
-/*	$OpenBSD: seekdir.c,v 1.10 2013/11/05 20:36:51 schwarze Exp $ */
+/*	$OpenBSD: seekdir.c,v 1.11 2013/11/06 20:35:25 schwarze Exp $ */
 /*
- * Copyright (c) 1983, 1993
- *	The Regents of the University of California.  All rights reserved.
+ * Copyright (c) 2013 Ingo Schwarze <schwarze@openbsd.org>
  *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the above copyright
- *    notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- *    notice, this list of conditions and the following disclaimer in the
- *    documentation and/or other materials provided with the distribution.
- * 3. Neither the name of the University nor the names of its contributors
- *    may be used to endorse or promote products derived from this software
- *    without specific prior written permission.
+ * Permission to use, copy, modify, and distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
  *
- * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
- * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
- * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
- * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
- * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
- * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
- * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
- * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  */
 
 #include <dirent.h>
@@ -41,7 +28,39 @@
 void
 seekdir(DIR *dirp, long loc)
 {
+	struct dirent *dp;
+
+	/*
+	 * First check whether the directory entry to seek for
+	 * is still buffered in the directory structure in memory.
+	 */
+
 	_MUTEX_LOCK(&dirp->dd_lock);
+	for (dirp->dd_loc = 0;
+	     dirp->dd_loc < dirp->dd_size;
+	     dirp->dd_loc += dp->d_reclen) {
+		dp = (struct dirent *)(dirp->dd_buf + dirp->dd_loc);
+		if (dp->d_off != loc)
+			continue;
+
+		/*
+		 * Entry found in the buffer, use it.  If readdir(3)
+		 * follows, this will save us a getdents(2) syscall.
+		 * Note that d_off is the offset of the _next_ entry,
+		 * so advance dd_loc.
+		 */
+
+		dirp->dd_loc += dp->d_reclen;
+		dirp->dd_curpos = loc;
+		_MUTEX_UNLOCK(&dirp->dd_lock);
+		return;
+	}
+
+	/*
+	 * The entry is not in the buffer, prepare a call to getdents(2).
+	 * In particular, invalidate dd_loc.
+	 */
+
 	dirp->dd_loc = 0;
 	dirp->dd_curpos = lseek(dirp->dd_fd, loc, SEEK_SET);
 	_MUTEX_UNLOCK(&dirp->dd_lock);