Add "bootstat --output-dir" option.

bootstat.h

-// 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.
 
 // Public API for the C and C++ bindings to the Chromium OS
 // 'bootstat' facility.  The facility is a simple timestamp
 // mechanism to associate a named event with the time that it
 // occurred and with other relevant statistics.
 
 #ifndef BOOTSTAT_H_
 #define BOOTSTAT_H_
 
 #if defined(__cplusplus)
 extern "C" {
 #endif
 
 //
 // Length of the longest valid string naming an event, including the
 // terminating NUL character.  Clients of bootstat_log() can use
 // this value for the size of buffers to hold event names; names
 // that exceed this buffer size will be truncated.
 //
 // This value is arbitrarily chosen, but see comments in
 // bootstat_log.c regarding implementation assumptions for this
 // value.
 //
 #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
 // significant.  Behavior in the presence of other characters is
 // unspecified - Caveat Emptor!
 //
 // Applications are responsible for establishing higher-level naming
 // 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
 #endif  // BOOTSTAT_H_