Android 内核初识(1)下载源码需求与教程

　　官方文档:　http://source.android.com/source/requirements.html 　　

Requirements

　　The Android build is routinely tested in-house on recent versions of Ubuntu LTS (14.04), but most distributions should have the required build tools available.

Before you download and build the Android source, ensure your system meets the following requirements:

• A Linux or Mac OS system. It is also possible to build Android in a virtual machine on unsupported systems such as Windows. If you are running Linux in a virtual machine, you need at least 16GB of RAM/swap and 100GB or more of disk space in order to build the Android tree. See disk size requirements below.
• A 64-bit environment is required for Gingerbread (2.3.x) and newer versions, including the master branch. You can compile older versions on 32-bit systems.
• At least 100GB of free disk space for a checkout, 150GB for a single build, and 200GB or more for multiple builds. If you employ ccache, you will need even more space.
• Python 2.6 -- 2.7, which you can download from python.org.
• GNU Make 3.81 -- 3.82, which you can download from gnu.org,
• JDK 7 to build the master branch of Android in the Android Open Source Project (AOSP); JDK 6 to build Gingerbread through KitKat; JDK 5 for Cupcake through Froyo. See Initializing a Build Environment for installation instructions by operating system.
• Git 1.7 or newer. You can find it at git-scm.com.

Downloading the Source

IN THIS DOCUMENT

1. Installing Repo
2. Initializing a Repo client
3. Downloading the Android Source Tree
4. Using Authentication
5. Troubleshooting network issues
6. Using a local mirror
7. Verifying Git Tags

The Android source tree is located in a Git repository hosted by Google. This document describes how to download the source tree for a specific Android code-line.

Installing Repo

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

To install Repo:

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

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

2,Download the Repo tool and ensure that it is executable:

$ curl https://storage.googleapis.com/git-repo-downloads/repo > ~/bin/repo
$ chmod a+x ~/bin/repo

For version 1.17, the SHA-1 checksum for repo is ddd79b6d5a7807e911b524cb223bc3544b661c28

For version 1.19, the SHA-1 checksum for repo is 92cbad8c880f697b58ed83e348d06619f8098e6c

For version 1.20, the SHA-1 checksum for repo is e197cb48ff4ddda4d11f23940d316e323b29671c

For version 1.21, the SHA-1 checksum for repo is b8bd1804f432ecf1bab730949c82b93b0fc5fede

For version 1.22, the SHA-1 checksum for repo is da0514e484f74648a890c0467d61ca415379f791

Initializing a Repo client

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

1,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

2,Run repo init to 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 various repositories included in the Android source will be placed within your working directory.

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

3,To check out a branch other than "master", specify it with -b. For a list of branches, see Source Code Tags and Builds.

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

　　When prompted, 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 a registered 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 should now contain a .repo directory where files such as the manifest will be kept.

Downloading the Android Source Tree

To pull down the Android source tree 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 directory under their project names. The initial sync operation will take an hour or more to complete. For more about repo sync and other Repo commands, see theDeveloping section.

Using Authentication

By default, access to the Android source code is anonymous. To protect the servers 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 many 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 with the password generator and follow the instructions on the password generator page.

The second step is to force authenticated access, by using the following manifest URI:https://android.googlesource.com/a/platform/manifest. Notice how the /a/ directory prefix triggers mandatory authentication. You can convert an 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 corporate 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, getting stuck in the middle of downloads (typically during "Receiving objects"). It has been reported that tweaking the settings of the TCP/IP stack and using non-parallel commands can improve the situation. You need root access to modify the TCP setting:

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

Using a local mirror

When using several 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). The download for a full mirror is smaller than the download of two clients, while containing more information.

These instructions assume that the mirror is created in /usr/local/aosp/mirror. The first step is to create and sync the mirror itself. Notice the --mirror flag, which can be specified only 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's important 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 synced against 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 over NFS, SSH or Git. It's also possible to store it on a removable drive and to 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)

mQGiBEnnWD4RBACt9/h4v9xnnGDou13y3dvOx6/t43LPPIxeJ8eX9WB+8LLuROSV
lFhpHawsVAcFlmi7f7jdSRF+OvtZL9ShPKdLfwBJMNkU66/TZmPewS4m782ndtw7
8tR1cXb197Ob8kOfQB3A9yk2XZ4ei4ZC3i6wVdqHLRxABdncwu5hOF9KXwCgkxMD
u4PVgChaAJzTYJ1EG+UYBIUEAJmfearb0qRAN7dEoff0FeXsEaUA6U90sEoVks0Z
wNj96SA8BL+a1OoEUUfpMhiHyLuQSftxisJxTh+2QclzDviDyaTrkANjdYY7p2cq
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jU5SA/9WwIps4SC84ielIXiGWEqq6i6/sk4I9q1YemZF2XVVKnmI1F4iCMtNKsR4
MGSa1gA8s4iQbsKNWPgp7M3a51JCVCu6l/8zTpA+uUGapw4tWCp4o0dpIvDPBEa9
b/aF/ygcR8mh5hgUfpF9IpXdknOsbKCvM9lSSfRciETykZc4wrRCVGhlIEFuZHJv
aWQgT3BlbiBTb3VyY2UgUHJvamVjdCA8aW5pdGlhbC1jb250cmlidXRpb25AYW5k
cm9pZC5jb20+iGAEExECACAFAknnWD4CGwMGCwkIBwMCBBUCCAMEFgIDAQIeAQIX
gAAKCRDorT+BmrEOeNr+AJ42Xy6tEW7r3KzrJxnRX8mij9z8tgCdFfQYiHpYngkI
2t09Ed+9Bm4gmEO5Ag0ESedYRBAIAKVW1JcMBWvV/0Bo9WiByJ9WJ5swMN36/vAl
QN4mWRhfzDOk/Rosdb0csAO/l8Kz0gKQPOfObtyYjvI8JMC3rmi+LIvSUT9806Up
hisyEmmHv6U8gUb/xHLIanXGxwhYzjgeuAXVCsv+EvoPIHbY4L/KvP5x+oCJIDbk
C2b1TvVk9PryzmE4BPIQL/NtgR1oLWm/uWR9zRUFtBnE411aMAN3qnAHBBMZzKMX
LWBGWE0znfRrnczI5p49i2YZJAjyX1P2WzmScK49CV82dzLo71MnrF6fj+Udtb5+
OgTg7Cow+8PRaTkJEW5Y2JIZpnRUq0CYxAmHYX79EMKHDSThf/8AAwUIAJPWsB/M
pK+KMs/s3r6nJrnYLTfdZhtmQXimpoDMJg1zxmL8UfNUKiQZ6esoAWtDgpqt7Y7s
KZ8laHRARonte394hidZzM5nb6hQvpPjt2OlPRsyqVxw4c/KsjADtAuKW9/d8phb
N8bTyOJo856qg4oOEzKG9eeF7oaZTYBy33BTL0408sEBxiMior6b8LrZrAhkqDjA
vUXRwm/fFKgpsOysxC6xi553CxBUCH2omNV6Ka1LNMwzSp9ILz8jEGqmUtkBszwo
G1S8fXgE0Lq3cdDM/GJ4QXP/p6LiwNF99faDMTV3+2SAOGvytOX6KjKVzKOSsfJQ
hN0DlsIw8hqJc0WISQQYEQIACQUCSedYRAIbDAAKCRDorT+BmrEOeCUOAJ9qmR0l
EXzeoxcdoafxqf6gZlJZlACgkWF7wi2YLW3Oa+jv2QSTlrx4KLM=
=Wi5D
-----END PGP PUBLIC KEY BLOCK-----

After importing the keys, you can verify any tag with

$ git tag -v TAG_NAME

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