[Android (2)] download the android source code tree

This article is mainly taken from: http://source.android.com/source/downloading.html, and added Annotation

Installing Repo

Repo is a tool that makes it easier to work with Git in the context of Android. For more information about Repo, seeVersion Control.

To install, initialize, and configure Repo, follow these steps:

• Make sure you have a bin/directory in your home directory, and that it is stored in your path:

  $ mkdir ~/bin$ PATH=~/bin:$PATH

• Download the Repo script and ensure it is executable:

  $ curl https://dl-ssl.google.com/dl/googlesource/git-repo/repo > ~/bin/repo$ chmod a+x ~/bin/repo

• The SHA-1 checksum for repo is 29ba4221d4fccdfa8d87931cd73466fdc24040b5

Initializing a Repo client

After installing Repo, set up your client to access the android source repository:

• Create an empty directory to hold your working files. If you're using MacOS, this has to be on a case-sensitive filesystem. Give it any name you like:

  $ mkdir WORKING_DIRECTORY$ cd WORKING_DIRECTORY

• Runrepo initTo bring down the latest version of Repo with all its most recent bug fixes. you must specify a URL for the manifest, which specifies where the varous repositories has been ded in the Android source will be placed within your working
  Directory.

  $ repo init -u https://android.googlesource.com/platform/manifest

  To check out a branch other than "master", specify it with-B:

  $ repo init -u https://android.googlesource.com/platform/manifest -b android-4.0.1_r1

• When prompted, Please configure repo with your real name and email address. To use the Gerrit code-review tool, you will need an email address that is connected with aregistered Google account. Make sure this
  Is a live address at which you can receive messages. The name that you provide here will show up in attributions for your code submissions.

A successful initialization will end with a message stating that Repo is initialized in your working directory. Your client directory shocould now contain.repoDirectory where files such as the manifest will be kept.

Note: For details about Repo and Git usage, see:

Repo: http://source.android.com/source/using-repo.html

Git: Git Magic. You can find the Chinese version of this book online.

Getting the files

To pull down files to your working directory from the repositories as specified in the default manifest, run

$ repo sync

The Android source files will be located in your working directoryunder their project names. The initial sync operation will takean hour or more to complete. For more aboutrepo syncAnd otherRepo commands, seeVersion
Control.

Using authentication

By default, access to the Android source code is anonymous. To protect thes ervers against excessive usage, each IP address is associated with a quota.

When sharing an IP address with other users (e.g. when accessing the source repositories from beyond a NAT firewall), the quotas can trigger even for regular usage patterns (e.g. if your users sync new clients from the same IP address within a short period ).

In that case, it is possible to use authenticated access, which then uses a separate quota for each user, regardless of the IP address.

The first step is to create a password from
The password generator and to save it in~/.netrcAccording to the instructions on that page.

The second step is to force authenticated access, by using the following manifest URI:https://android.googlesource.com/a/platform/manifest. Noticehow/a/Directory prefix triggers mandatory authentication. You can convert
Existing client to use mandatory authentication with the following command:

$ repo init -u https://android.googlesource.com/a/platform/manifest

Troubleshooting network issues

When downloading from behind a proxy (which is common in some unknown ate environments), it might be necessary to explicitly specify the proxy that is then used by repo:

$ export HTTP_PROXY=http://<proxy_user_id>:<proxy_password>@<proxy_server>:<proxy_port>$ export HTTPS_PROXY=http://<proxy_user_id>:<proxy_password>@<proxy_server>:<proxy_port>

More rarely, Linux clients experience connectivity issues, gettingstuck in the middle of downloads (typically during "sorting objects "). it has been reported that tweaking the settings of the TCP/IP stack andusing non-parallel commands can improve the situation.
You need rootaccess to modify the TCP setting:

$ sudo sysctl -w net.ipv4.tcp_window_scaling=0$ repo sync -j1

Using a local mirror

When using specified clients, especially in situations where bandwidth is scarce, it is better to create a local mirror of the entire server content, and to sync clients from that mirror (which requires no network access ).

These instructions assume that the mirror is created in/usr/local/aosp/mirror. The first step is to create and sync the mirror itself, which uses close to10gb of network bandwidth and a similar amount of disk space. Notice--mirror
Flag, which can only be specified when creating a new client:

$ mkdir -p /usr/local/aosp/mirror$ cd /usr/local/aosp/mirror$ repo init -u https://android.googlesource.com/mirror/manifest --mirror$ repo sync

Once the mirror is synced, new clients can be created from it. Note that it 'ortortant to specify an absolute path:

$ mkdir -p /usr/local/aosp/master$ cd /usr/local/aosp/master$ repo init -u /usr/local/aosp/mirror/platform/manifest.git$ repo sync

Finally, to sync a client against the server, the mirror needs to be syncedagainst the server, then the client against the mirror:

$ cd /usr/local/aosp/mirror$ repo sync$ cd /usr/local/aosp/master$ repo sync

It's possible to store the mirror on a LAN server and to access it overNFS, SSH or Git. it's also possible to store it on a removable drive andto pass that drive around between users or between machines.

Verifying Git Tags

Load the following public key into your GnuPG key database. The key is used to sign annotated tags that represent releases.

$ gpg --import

Copy and paste the key (s) below, then enter EOF (Ctrl-D) to end the input and process the keys.

-----BEGIN PGP PUBLIC KEY BLOCK-----Version: GnuPG v1.4.2.2 (GNU/Linux)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Wi5D-----END PGP PUBLIC KEY BLOCK-----

After importing the keys, you can verify any tag

$ git tag -v TAG_NAME

If you haven't
Set up ccache yet, now wocould be a good time to do it.

Next: Build the code

You now have a complete local copy of the Android codebase. Continue on
Building ....