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When we write a commit, we include data that is specific to the hash algorithm, such as parents and the root tree. In order to write both a SHA-1 commit and a SHA-256 version, we need to convert between them. However, a straightforward conversion isn't necessarily what we want. When we sign a commit, we sign its data, so if we create a commit for SHA-256 and then write a SHA-1 version, we'll still have only signed the SHA-256 data. While this is valid, it would be better to sign both forms of data so people using SHA-1 can verify the signatures as well. Consequently, we don't want to use the standard mapping that occurs when we write an object. Instead, let's move most of the writing of the commit into a separate function which is agnostic of the hash algorithm and which simply writes into a buffer and specify both versions of the object ourselves. We can then call this function twice: once with the SHA-256 contents, and if SHA-1 is enabled, once with the SHA-1 contents. If we're signing the commit, we then sign both versions and append both signatures to both buffers. To produce a consistent hash, we always append the signatures in the order in which Git implemented them: first SHA-1, then SHA-256. In order to make this signing code work, we split the commit signing code into two functions, one which signs the buffer, and one which appends the signature. Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>
Git - fast, scalable, distributed revision control system
Git is a fast, scalable, distributed revision control system with an unusually rich command set that provides both high-level operations and full access to internals.
Git is an Open Source project covered by the GNU General Public License version 2 (some parts of it are under different licenses, compatible with the GPLv2). It was originally written by Linus Torvalds with help of a group of hackers around the net.
Please read the file INSTALL for installation instructions.
Many Git online resources are accessible from https://git-scm.com/ including full documentation and Git related tools.
See Documentation/gittutorial.txt to get started, then see
Documentation/giteveryday.txt for a useful minimum set of commands, and
Documentation/git-<commandname>.txt for documentation of each command.
If git has been correctly installed, then the tutorial can also be
read with man gittutorial or git help tutorial, and the
documentation of each command with man git-<commandname> or git help <commandname>.
CVS users may also want to read Documentation/gitcvs-migration.txt
(man gitcvs-migration or git help cvs-migration if git is
installed).
The user discussion and development of Git take place on the Git mailing list -- everyone is welcome to post bug reports, feature requests, comments and patches to git@vger.kernel.org (read Documentation/SubmittingPatches for instructions on patch submission and Documentation/CodingGuidelines).
Those wishing to help with error message, usage and informational message
string translations (localization l10) should see po/README.md
(a po file is a Portable Object file that holds the translations).
To subscribe to the list, send an email with just "subscribe git" in the body to majordomo@vger.kernel.org (not the Git list). The mailing list archives are available at https://lore.kernel.org/git/, http://marc.info/?l=git and other archival sites.
Issues which are security relevant should be disclosed privately to the Git Security mailing list git-security@googlegroups.com.
The maintainer frequently sends the "What's cooking" reports that list the current status of various development topics to the mailing list. The discussion following them give a good reference for project status, development direction and remaining tasks.
The name "git" was given by Linus Torvalds when he wrote the very first version. He described the tool as "the stupid content tracker" and the name as (depending on your mood):
- random three-letter combination that is pronounceable, and not actually used by any common UNIX command. The fact that it is a mispronunciation of "get" may or may not be relevant.
- stupid. contemptible and despicable. simple. Take your pick from the dictionary of slang.
- "global information tracker": you're in a good mood, and it actually works for you. Angels sing, and a light suddenly fills the room.
- "goddamn idiotic truckload of sh*t": when it breaks