git-dissect: DIStributed biSECT

git-dissect is an alternative to git bisect that allows running tests on multiple hosts in order to bisect faster.
It was inspired by Rob Hoelz's git-pisect.

Installation

$ git clone https://github.com/talshorer/git-dissect.git
$ cd git-dissect
$ # Install for the current user only
$ ./setup.py install --user
$ # Install for everyone using the system
$ sudo ./setup.py install

Usage

Start as you would start a normal bisect:

$ git bisect start --no-checkout
$ git bisect bad $BAD_COMMIT
$ git bisect good $GOOD_COMMIT

Note: It is recommended to start git bisect with the --no-checkout option when using git-dissect.

Configuration

git-dissect uses git's configuration to describe its hosts. Each host is described by a subsection called dissect.<host>, containing the following values:

Value	Description	Mandatory	Default
enabled	Whether to include this host when performnig operations	no	true
path	Path to the repository on the host. Can be absolute or relative to the user's home directory	yes	-
user	User to log in with	no	Current user
hostname	Alternative hostname/address to connect to (similar to ssh_config)	no	Subsection's name
port	SSH port used to connect to the host	no	22
stricthostkeychecking	Use SSH known_hosts mechanism. Disabling this can pose a security risk	no	true
proxycommand	Proxy command to use instead of TCP connection. The special value "none" is the same as not providing a proxy command (similar to ssh_config).	no	"none"

git-dissect will use all hosts with a path value.
It is possible to specify the same machine multiple types with different subsection names and paths.
Missing values will be taken from SSH's default configuration files before resorting to the default value for a given option. To disable reading SSH's configuration, set dissect.usesshconfig to false in gitconfig (see example).
It is recommended to set options other than path and enabled globally (see example) for easier management of multiple repositories using the same hosts.
Note: In order for git-dissect to work properly, the user must be able to log in to the hosts via SSH using a public key.

Examples

Add a new host

$ git config --global dissect.bravo.user tal
$ git config --global dissect.bravo.hostname 20.0.1.2
$ git config --global dissect.bravo.port 7401
$ git config dissect.bravo.path /home/tal/dissect-example

Remove a host

$ git config --unset dissect.bravo.path

Note: you might want to disable a host instead of removing it

Disable a host

$ git config --bool dissect.bravo.enabled false

Enable a host

$ git config --bool dissect.bravo.enabled true

Disable reading SSH's configuration

$ git config --bool dissect.usesshconfig false

Complete configuration

[dissect]
	usesshconfig = true
[dissect "20.0.0.2"]
	path = /tmp/dissect-example
	user = root
	port = 7400
	stricthostkeychecking = false
[dissect "alpha"]
	path = dissect-example
	stricthostkeychecking = true
[dissect "bravo"]
	enabled = true
	path = /home/tal/dissect-example
	user = tal
	hostname = 20.0.1.2
	port = 7401
[dissect "charlie1"]
	enabled = false
	path = repos/dissect-example1
	user = tals
	hostname = charlie
[dissect "charlie2"]
	path = repos/dissect-example2
	user = tals
	hostname = charlie
[dissect "delta"]
	path = /dissect-example
	port 6500
	proxycommand = nc localohst %p

git-dissect commands:

Command	Description
git dissect execute <cmd>	Run <cmd> on all hosts. The remote repository path is used as the working directory.
git dissect fetch	Run git fetch on all hosts.
git dissect checkout	Choose a commit for each host and run git checkout on all hosts.
git dissect collect <cmd>	Run <cmd> on all hosts and use the exit code to determine if a commit is good or bad.
git dissect step <cmd>	Equivalent to running git dissect checkout; git dissect collect <cmd>.
git dissect run <cmd>	Equivalent to running git dissect step <cmd> until the bad commit is found.
git dissect signal {wait|good|bad}	See "Manual mode" below.

Manual mode

When not supplying a command to git dissect {execute|collect|step|run}, git-dissect will run in "manual mode".
The actual command that's executed on the hosts is git dissect signal wait, which waits for the user to invoke git dissect signal {good|bad} on the host to indicate whether the checked out commit is good or bad. Execution of git-dissect then continues normally as if the remote command succeeded or failed as indicated by the user.
This is equivalent to calling git bisect {good|bad} after running tests manually.
Note: Since git dissect signal runs on the host, git-dissect must be installed on it in order to use manual mode.

Alternatively, if you don't want to install git-dissect on the hosts, you can run git bisect {good|bad} dissect/<host> to manually mark the commit checked out on <host> as good or bad.
Note that this does not remove the host from the list of hosts that git dissect collect runs on. To achieve that, run git update-ref -d refs/dissect/<host>.

Future

• Better handling of error conditions.
• Add subcommands for easier host management.
• If git dissect collect is interrupted after some information was collected, call git bisect with what we have instead of throwing everything away.
• Upload to PyPI and update installation accordingly.