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Taylor Blau 492ba81346 string-list: introduce string_list_setlen() 
It is sometimes useful to reduce the size of a `string_list`'s list of
items without having to re-allocate them. For example, doing the
following:

    struct strbuf buf = STRBUF_INIT;
    struct string_list parts = STRING_LIST_INIT_NO_DUP;
    while (strbuf_getline(&buf, stdin) != EOF) {
      parts.nr = 0;
      string_list_split_in_place(&parts, buf.buf, ":", -1);
      /* ... */
    }
    string_list_clear(&parts, 0);

is preferable over calling `string_list_clear()` on every iteration of
the loop. This is because `string_list_clear()` causes us free our
existing `items` array. This means that every time we call
`string_list_split_in_place()`, the string-list internals re-allocate
the same size array.

Since in the above example we do not care about the individual parts
after processing each line, it is much more efficient to pretend that
there aren't any elements in the `string_list` by setting `list->nr` to
0 while leaving the list of elements allocated as-is.

This allows `string_list_split_in_place()` to overwrite any existing
entries without needing to free and re-allocate them.

However, setting `list->nr` manually is not safe in all instances. There
are a couple of cases worth worrying about:

  - If the `string_list` is initialized with `strdup_strings`,
    truncating the list can lead to overwriting strings which are
    allocated elsewhere. If there aren't any other pointers to those
    strings other than the ones inside of the `items` array, they will
    become unreachable and leak.

    (We could ourselves free the truncated items between
    string_list->items[nr] and `list->nr`, but no present or future
    callers would benefit from this additional complexity).

  - If the given `nr` is larger than the current value of `list->nr`,
    we'll trick the `string_list` into a state where it thinks there are
    more items allocated than there actually are, which can lead to
    undefined behavior if we try to read or write those entries.

Guard against both of these by introducing a helper function which
guards assignment of `list->nr` against each of the above conditions.

Co-authored-by: Jeff King <peff@peff.net>
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2023-04-24 16:01:28 -07:00
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README.md

Build status

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