bisect.py is a wrapper around the general purpose binary_search_state.py. It
provides a user friendly interface for bisecting various compilation errors.
The 2 currently provided methods of bisecting are ChromeOS package and object
bisection. Each method defines a default set of options to pass to
binary_search_state.py and allow the user to override these defaults (see
the "Overriding" section).

** NOTE **
All commands, examples, scripts, etc. are to be run from your chroot unless
stated otherwise.

Bisection Methods:

1) ChromeOS Package:
  This method will bisect across all packages in a ChromeOS repository and find
  the offending packages (according to your test script). This method takes the
  following arguments:

    board: The board to bisect on. For example: daisy, falco, etc.
    remote: The IP address of the physical machine you're using to test with.

  By default the ChromeOS package method will do a simple interactive test that
  pings the machine and prompts the user if the machine is good.

  a) Setup:
    The ChromeOS package method requires that you have three build trees:

      /build/${board}.bad  - The build tree for your "bad" build
      /build/${board}.good - The build tree for your "good" build
      /build/${board}.work - A full copy of /build/${board}.bad

  b) Cleanup:
    bisect.py does most cleanup for you, the only thing required by the user is
    to cleanup all built images and the three build trees made in /build/

  c) Default Arguments:
    --get_initial_items='cros_pkg/get_initial_items.sh'
    --switch_to_good='cros_pkg/switch_to_good.sh'
    --switch_to_bad='cros_pkg/switch_to_bad.sh'
    --test_setup_script='cros_pkg/test_setup.sh'
    --test_script='cros_pkg/interactive_test.sh'
    --incremental
    --prune
    --file_args

  d) Additional Documentation:
    See ./cros_pkg/README.cros_pkg_triage for full documentation of ChromeOS
    package bisection.

  e) Examples:
    i)  Basic interactive test package bisection, on daisy board:
        ./bisect.py package daisy 172.17.211.184

    ii) Basic boot test package bisection, on daisy board:
        ./bisect.py package daisy 172.17.211.184 -t cros_pkg/boot_test.sh

2) ChromeOS Object:
  This method will bisect across all objects in a ChromeOS package and find
  the offending objects (according to your test script). This method takes the
  following arguments:

    board: The board to bisect on. For example: daisy, falco, etc.
    remote: The IP address of the physical machine you're using to test with.
    package: The package to bisect with. For example: chromeos-chrome
    dir: (Optional) the directory for your good/bad build trees. Defaults to
         $BISECT_DIR or /tmp/sysroot_bisect. This value will set $BISECT_DIR
         for all bisecting scripts.

  By default the ChromeOS object method will do a simple interactive test that
  pings the machine and prompts the user if the machine is good.

  a) Setup:
    The ChromeOS package method requires that you populate your good and bad set
    of objects. sysroot_wrapper will automatically detect the BISECT_STAGE
    variable and use this to populate emerged objects. Here is an example:

      # Defaults to /tmp/sysroot_bisect
      export BISECT_DIR="/path/to/where/you/want/to/store/builds/"

      export BISECT_STAGE="POPULATE_GOOD"
      ./switch_to_good_compiler.sh
      emerge-${board} -C ${package_to_bisect}
      emerge-${board} ${package_to_bisect}

      export BISECT_STAGE="POPULATE_BAD"
      ./switch_to_bad_compiler.sh
      emerge-${board} -C {package_to_bisect}
      emerge-${board} ${package_to_bisect}

  b) Cleanup:
    The user must clean up all built images and the populated object files.

  c) Default Arguments:
    --get_initial_items='sysroot_wrapper/get_initial_items.sh'
    --switch_to_good='sysroot_wrapper/switch_to_good.sh'
    --switch_to_bad='sysroot_wrapper/switch_to_bad.sh'
    --test_setup_script='sysroot_wrapper/test_setup.sh'
    --test_script='sysroot_wrapper/interactive_test.sh'
    --noincremental
    --prune
    --file_args

  d) Additional Documentation:
    See ./sysroot_wrapper/README for full documentation of ChromeOS object file
    bisecting.

  e) Examples:
    i)  Basic interactive test object bisection, on daisy board for
        cryptohome package:
        ./bisect.py object daisy 172.17.211.184 cryptohome

    ii) Basic boot test package bisection, on daisy board for cryptohome
        package:
        ./bisect.py object daisy 172.17.211.184 cryptohome \
        --test_script=sysroot_wrapper/boot_test.sh

3) Android object:
  NOTE: Because this isn't a ChromeOS bisection tool, the concept of a
        chroot doesn't exist. Just run this tool from a normal shell.

  This method will bisect across all objects in the Android source tree and
  find the offending objects (according to your test script). This method takes
  the following arguments:

    android_src: The location of your android source tree
    num_jobs: (Optional) The number of jobs to pass to make. This is dependent
              on how many cores your machine has. A good number is probably
	      somewhere around 5 to 10.
    device_id: (Optional) The serial code for the device you are testing on.
               This is used to determine which device should be used in case
	       multiple devices are plugged into your computer. You can get
	       serial code for your device by running "adb devices".
    dir: (Optional) the directory for your good/bad build trees. Defaults to
         $BISECT_DIR or ~/ANDROID_BISECT/. This value will set $BISECT_DIR
         for all bisecting scripts.

  By default the Android object method will do a simple interactive test that
  pings the machine and prompts the user if the machine is good.

  a) Setup:
    The Android object method requires that you populate your good and bad set
    of objects. The Android compiler wrapper will automatically detect the
    BISECT_STAGE variable and use this to populate emerged objects. Here is an
    example:

      # Defaults to ~/ANDROID_BISECT/
      export BISECT_DIR="/path/to/where/you/want/to/store/builds/"

      export BISECT_STAGE="POPULATE_GOOD"
      # Install the "good" compiler
      ./switch_to_good_compiler.sh
      make clean
      make -j <your_preferred_number_of_jobs>

      export BISECT_STAGE="POPULATE_BAD"
      # Install the "bad" compiler
      ./switch_to_bad_compiler.sh
      make clean
      make -j <your_preferred_number_of_jobs>

  b) Cleanup:
    The user must clean up all built images and the populated object files.

  c) Default Arguments:
    --get_initial_items='android/get_initial_items.sh'
    --switch_to_good='android/switch_to_good.sh'
    --switch_to_bad='android/switch_to_bad.sh'
    --test_setup_script='android/test_setup.sh'
    --test_script='android/interactive_test.sh'
    --incremental
    --prune
    --file_args

  d) Additional Documentation:
    See ./android/README.android for full documentation of Android object file
    bisecting.

  e) Examples:
    i)  Basic interactive test android bisection, where the android source is
        at ~/android_src:
        ./bisect.py android ~/android_src

    ii) Basic boot test android bisection, where the android source is at
        ~/android_src, and 10 jobs will be used to build android:
        ./bisect.py android ~/android_src --num_jobs=10 \
        --test_script=sysroot_wrapper/boot_test.sh

Resuming:
  bisect.py and binary_search_state.py offer the ability to resume a bisection
  in case it was interrupted by a SIGINT, power failure, etc. Every time the
  tool completes a bisection iteration its state is saved to disk (usually to
  the file "./bisect.py.state"). If passed the --resume option, the tool
  it will automatically detect the state file and resume from the last
  completed iteration.

Overriding:
  You can run ./bisect.py --help or ./binary_search_state.py --help for a full
  list of arguments that can be overriden. Here are a couple of examples:

  Example 1 (do boot test instead of interactive test):
  ./bisect.py package daisy 172.17.211.182 --test_script=cros_pkg/boot_test.sh

  Example 2 (do package bisector system test instead of interactive test, this
             is used to test the bisecting tool itself -- see comments in
             hash_test.sh for more details):
  ./bisect.py package daisy 172.17.211.182 \
    --test_script=common/hash_test.sh --test_setup_script=""

  Example 3 (enable verbose mode, disable pruning, and disable verification):
  ./bisect.py package daisy 172.17.211.182 \
  --verbose --prune=False --verify=False