Add new bootstat_get_last command

README

 Copyright (c) 2010 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.
 
 This is the Chromium OS 'bootstat' utility.  The utility is used
 to generate timestamps and other performance statistics during
 system boot.
 
-==== Functional specification
-Usage:
+==== Command specifications
+'bootstat' command usage:
     bootstat <event-name>
 
 Summary:  The command gathers and records the contents of
 /proc/uptime and disk statistics for the boot disk (the full disk,
 not the boot partition), and associates the data with the passed
 in <event-name>.
 
+----
+'bootstat_last' command usage:

[petkov, 2010/12/04 00:00:55]

I'd suggest a better name but I don't have any better suggestions :/ Maybe
bootstat_dump?

+    bootstat_last <event-name> [ <stat> ... ]
+
+Summary:  Print on standard output the value of selected statistics
+recorded when a specified event occurred.  These are the available
+statistics:
+    time:  Total time since kernel startup at the time of the event.
+    read-sectors:  Total sectors read from any partition of the boot
+        device since kernel startup.
+    write-sectors:  Total sectors written to any partition of the
+        boot device since kernel startup.
+
+If multiple statistics requested, they are reported in order, one
+per line.  If no statistics are listed on the command line, the
+default is to report 'time'.
+
+If an event has occurred more than once since kernel startup, only
+the statistics from the last occurrence are reported.
+
 ==== API specification
 The C and C++ API is defined in "bootstat.h".  See that header for
 specification details.
 
 ==== Design and implementation details
 Uptime data are stored in a file named /tmp/uptime-<event-name>;
 disk statistics are stored in a file named /tmp/disk-<event-name>.
 This convention is a concession to pre-existing code that depends on
 these files existing with these specific names, including the
 platform_BootPerf test in autotest, the boot-complete upstart job,
 and the Chrome code to report boot time on the login screen.
 
 New code should treat the file names as an implementation detail,
 not as the interface.  You should not add new code that depends on
 the file names; instead, you should enhance the bootstat command
 and/or library to provide access to the data you need.
 
 ==== Code conventions
 This is currently C code, because a) the code is required for use
 as a library accessible to both C and C++ code, and b) it's too
 small to justify the boilerplate required to have separate C and
 C++ bindings.  However, if the program grows, it may be appropriate
 to convert all or part to C++.
 
 To the extent that the code can be acceptable both to C and C++
 compilers, it should also adhere to Google's C++ coding conventions.
 In areas where the code is C specific, use your best judgement (note
 that Google also has Objective-C coding conventions that may be
 useful).