From: Junio C Hamano <gitster@pobox•com>
To: "Nguyễn Thái Ngọc Duy" <pclouds@gmail•com>
Cc: git@vger•kernel.org, Nicolas Pitre <nico@fluxnic•net>
Subject: Re: [PATCH] Document pack v4 format
Date: Tue, 27 Aug 2013 11:25:02 -0700 [thread overview]
Message-ID: <xmqqzjs3c7pd.fsf@gitster.dls.corp.google.com> (raw)
In-Reply-To: <1377602225-30439-1-git-send-email-pclouds@gmail.com> ("Nguyễn Thái Ngọc Duy"'s message of "Tue, 27 Aug 2013 18:17:05 +0700")
Nguyễn Thái Ngọc Duy <pclouds@gmail•com> writes:
> Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail•com>
> ---
> For my education but may help people who are interested in the
> format. Most is gathered from commit messages, except the delta tree
> entries.
Thanks.
> diff --git a/Documentation/technical/pack-format-v4.txt b/Documentation/technical/pack-format-v4.txt
In the final version it may be a good idea to either have this
together with the documentation for the existing pack-formats, or
add a reference from the documentation for the existing formats to
point at this new file saying "for v4 see ...".
> new file mode 100644
> index 0000000..9123a53
> --- /dev/null
> +++ b/Documentation/technical/pack-format-v4.txt
> @@ -0,0 +1,110 @@
> +Git pack v4 format
> +==================
> +
> +== pack-*.pack files have the following format:
> +
> + - A header appears at the beginning and consists of the following:
> +
> + 4-byte signature:
> + The signature is: {'P', 'A', 'C', 'K'}
> +
> + 4-byte version number (network byte order): must be version
> + number 4
> +
> + 4-byte number of objects contained in the pack (network byte
> + order)
> +
> + - (20 * nr_objects)-byte SHA-1 table: sorted in memcmp() order.
> +
> + - Commit name dictionary: the uncompressed length in variable
> + encoding, followed by zlib-compressed dictionary. Each entry
> + consists of two prefix bytes storing timezone followed by a
> + NUL-terminated string.
The log and code use different names to call this thing. "commit
name" is misleading (e.g. it is not "commit object name", but "names
recorded in commit objects"; it is not only for "committer" names,
but also applies to authors; it is not just names but also emails
and TZ used). Perhaps a better name would be "ident" table, as we
use the word "ident" only to refer to data to refer to people who
are recorded on either author/committer/tagger lines of the objects?
> + (undeltified representation)
> + n-byte type and length (4-bit type, (n-1)*7+4-bit length)
> + [uncompressed data]
> + [compressed data]
These two lines are not useful; it is better spelled as [data
specific to object type] as you have to enumerate what are stored
and how for each type separately anyway.
> +=== Tree representation
> +
> + - n-byte type and length (4-bit type, (n-1)*7+4-bit length)
> +
> + - Number of trees in variable length encoding
> +
> + - A number of trees, each consists of
The above "number of trees" sounds both wrong; aren't they the
number of "tree entries" (that can be blobs or subtrees) this tree
object records?
> + Path component reference: an index, in variable length encoding,
> + into tree path dictionary, which also covers entry mode.
> +
> + SHA-1 in SHA-1 reference encoding.
> +
> +Path component reference zero is an indicator of deltified portion and
> +has the following format:
> +
> + - path component reference: zero
> +
> + - index of the entry to copy from, in variable length encoding
> +
> + - number of entries in variable length encoding
> +
> + - base tree in SHA-1 reference encoding
> +
> +=== SHA-1 reference encoding
> +
> +This encoding is used to encode SHA-1 efficiently if it's already in
> +the SHA-1 table. It starts with an index number in variable length
> +encoding. If it's not zero, its value minus one is the index in the
> +SHA-1 table. If it's zero, 20 bytes of SHA-1 is followed.
next prev parent reply other threads:[~2013-08-27 18:25 UTC|newest]
Thread overview: 83+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-08-27 4:25 [PATCH 00/23] Preliminary pack v4 support Nicolas Pitre
2013-08-27 4:25 ` [PATCH 01/23] pack v4: initial pack dictionary structure and code Nicolas Pitre
2013-08-27 15:08 ` Junio C Hamano
2013-08-27 16:13 ` Nicolas Pitre
2013-08-27 4:25 ` [PATCH 02/23] export packed_object_info() Nicolas Pitre
2013-08-27 4:25 ` [PATCH 03/23] pack v4: scan tree objects Nicolas Pitre
2013-08-27 4:25 ` [PATCH 04/23] pack v4: add tree entry mode support to dictionary entries Nicolas Pitre
2013-08-27 4:25 ` [PATCH 05/23] pack v4: add commit object parsing Nicolas Pitre
2013-08-27 15:26 ` Junio C Hamano
2013-08-27 16:47 ` Nicolas Pitre
2013-08-27 17:42 ` Junio C Hamano
2013-08-27 4:25 ` [PATCH 06/23] pack v4: split the object list and dictionary creation Nicolas Pitre
2013-08-27 4:25 ` [PATCH 07/23] pack v4: move to struct pack_idx_entry and get rid of our own struct idx_entry Nicolas Pitre
2013-08-27 4:25 ` [PATCH 08/23] pack v4: basic references encoding Nicolas Pitre
2013-08-27 15:29 ` Junio C Hamano
2013-08-27 15:53 ` Nicolas Pitre
2013-08-27 4:25 ` [PATCH 09/23] pack v4: commit object encoding Nicolas Pitre
2013-08-27 15:39 ` Junio C Hamano
2013-08-27 16:50 ` Nicolas Pitre
2013-08-27 19:59 ` Nicolas Pitre
2013-08-27 20:15 ` Junio C Hamano
2013-08-27 21:43 ` Nicolas Pitre
2013-09-02 20:48 ` Duy Nguyen
2013-09-03 6:30 ` Nicolas Pitre
2013-09-03 7:41 ` Duy Nguyen
2013-09-05 3:50 ` Nicolas Pitre
2013-08-27 4:25 ` [PATCH 10/23] pack v4: tree " Nicolas Pitre
2013-08-27 15:44 ` Junio C Hamano
2013-08-27 16:52 ` Nicolas Pitre
2013-08-27 4:25 ` [PATCH 11/23] pack v4: dictionary table output Nicolas Pitre
2013-08-27 4:25 ` [PATCH 12/23] pack v4: creation code Nicolas Pitre
2013-08-27 15:48 ` Junio C Hamano
2013-08-27 16:59 ` Nicolas Pitre
2013-08-27 4:25 ` [PATCH 13/23] pack v4: object headers Nicolas Pitre
2013-08-27 4:25 ` [PATCH 14/23] pack v4: object data copy Nicolas Pitre
2013-08-27 15:53 ` Junio C Hamano
2013-08-27 18:24 ` Nicolas Pitre
2013-08-27 4:25 ` [PATCH 15/23] pack v4: object writing Nicolas Pitre
2013-08-27 4:26 ` [PATCH 16/23] pack v4: tree object delta encoding Nicolas Pitre
2013-08-27 4:26 ` [PATCH 17/23] pack v4: load delta candidate for encoding tree objects Nicolas Pitre
2013-08-27 4:26 ` [PATCH 18/23] pack v4: honor pack.compression config option Nicolas Pitre
2013-08-27 4:26 ` [PATCH 19/23] pack v4: relax commit parsing a bit Nicolas Pitre
2013-08-27 4:26 ` [PATCH 20/23] pack index v3 Nicolas Pitre
2013-08-27 4:26 ` [PATCH 21/23] pack v4: normalize pack name to properly generate the pack index file name Nicolas Pitre
2013-08-27 4:26 ` [PATCH 22/23] pack v4: add progress display Nicolas Pitre
2013-08-27 4:26 ` [PATCH 23/23] initial pack index v3 support on the read side Nicolas Pitre
2013-08-31 11:45 ` Duy Nguyen
2013-09-03 6:09 ` Nicolas Pitre
2013-09-03 7:34 ` Duy Nguyen
2013-08-27 11:17 ` [PATCH] Document pack v4 format Nguyễn Thái Ngọc Duy
2013-08-27 18:25 ` Junio C Hamano [this message]
2013-08-27 18:53 ` Nicolas Pitre
2013-08-31 2:49 ` [PATCH v2] " Nguyễn Thái Ngọc Duy
2013-09-03 6:00 ` Nicolas Pitre
2013-09-03 6:46 ` Nicolas Pitre
2013-09-03 11:49 ` Duy Nguyen
2013-09-03 14:54 ` Duy Nguyen
2013-09-05 4:12 ` Nicolas Pitre
2013-09-05 4:19 ` Duy Nguyen
2013-09-05 4:40 ` Nicolas Pitre
2013-09-05 5:04 ` Duy Nguyen
2013-09-05 5:39 ` Nicolas Pitre
2013-09-05 16:52 ` Duy Nguyen
2013-09-05 17:14 ` Nicolas Pitre
2013-09-05 20:26 ` Junio C Hamano
2013-09-05 21:04 ` Nicolas Pitre
2013-09-06 4:18 ` Duy Nguyen
2013-09-06 13:19 ` Nicolas Pitre
2013-09-06 2:14 ` [PATCH v3] " Nguyễn Thái Ngọc Duy
2013-09-06 3:23 ` Nicolas Pitre
2013-09-06 9:48 ` Duy Nguyen
2013-09-06 13:25 ` Nicolas Pitre
2013-09-06 13:44 ` Duy Nguyen
2013-09-06 16:44 ` Nicolas Pitre
2013-09-07 4:57 ` Nicolas Pitre
2013-09-07 4:52 ` Nicolas Pitre
2013-09-07 8:05 ` Duy Nguyen
2013-08-27 15:03 ` [PATCH 00/23] Preliminary pack v4 support Junio C Hamano
2013-08-27 15:59 ` Nicolas Pitre
2013-08-27 16:44 ` Junio C Hamano
2013-08-28 2:30 ` Duy Nguyen
2013-08-28 2:58 ` Nicolas Pitre
2013-08-28 3:06 ` Duy Nguyen
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