Add "bootstat --output-dir" option.

bootstat.h

Index: bootstat.h
diff --git a/bootstat.h b/bootstat.h
index d6b13d225e61fd0bbcb5f25c4c662281991eaaff..532a6da80bf2a65788f24a34d287ba19ba93c6e1 100644
--- a/bootstat.h
+++ b/bootstat.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+// Copyright (c) 2011 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
@@ -26,6 +26,8 @@ extern "C" {
 //
 #define BOOTSTAT_MAX_EVENT_LEN  64
 
+// bootstat_log()
+//
 // Log an event.  Event names should be composed of characters drawn
 // from this subset of 7-bit ASCII:  Letters (upper- or lower-case),
 // digits, dot ('.'), dash ('-'), and underscore ('_').  Case is
@@ -36,6 +38,23 @@ extern "C" {
 // conventions to prevent name collisions.
 extern void bootstat_log(const char* event_name);
 
+// bootstat_set_output_directory()
+//
+// Change the default directory into which bootstat_log() writes
+// timestamp files.  The input parameter is the directory path.
+// If the input parameter is NULL, the output directory is set
+// back to the initial default directory.
+//
+// bootstat_set_output_directory() checks its input path for
+// appropriate permissions when called.  If permissions to the
+// selected output directory are subsequently lost, bootstat_log()
+// fails silently.  The caller is responsible for selecting a
+// directory that is not subject to change.
+//
+// Returns 0 on success.  On failure, returns -1, with errno set as
+// for the access(2) system call.
+extern int bootstat_set_output_directory(const char*);
+
 #if defined(__cplusplus)
 }
 #endif