diff options
Diffstat (limited to 'Documentation')
24 files changed, 1156 insertions, 57 deletions
diff --git a/Documentation/Makefile b/Documentation/Makefile index 2415e0d657..471bb29725 100644 --- a/Documentation/Makefile +++ b/Documentation/Makefile @@ -67,6 +67,7 @@ SP_ARTICLES += howto/maintain-git API_DOCS = $(patsubst %.txt,%,$(filter-out technical/api-index-skel.txt technical/api-index.txt, $(wildcard technical/api-*.txt))) SP_ARTICLES += $(API_DOCS) +TECH_DOCS += technical/hash-function-transition TECH_DOCS += technical/http-protocol TECH_DOCS += technical/index-format TECH_DOCS += technical/pack-format diff --git a/Documentation/RelNotes/2.10.5.txt b/Documentation/RelNotes/2.10.5.txt new file mode 100644 index 0000000000..a498fd6fdc --- /dev/null +++ b/Documentation/RelNotes/2.10.5.txt @@ -0,0 +1,17 @@ +Git v2.10.5 Release Notes +========================= + +Fixes since v2.10.4 +------------------- + + * "git cvsserver" no longer is invoked by "git daemon" by default, + as it is old and largely unmaintained. + + * Various Perl scripts did not use safe_pipe_capture() instead of + backticks, leaving them susceptible to end-user input. They have + been corrected. + +Credits go to joernchen <joernchen@phenoelit.de> for finding the +unsafe constructs in "git cvsserver", and to Jeff King at GitHub for +finding and fixing instances of the same issue in other scripts. + diff --git a/Documentation/RelNotes/2.11.4.txt b/Documentation/RelNotes/2.11.4.txt new file mode 100644 index 0000000000..ad4da8eb09 --- /dev/null +++ b/Documentation/RelNotes/2.11.4.txt @@ -0,0 +1,17 @@ +Git v2.11.4 Release Notes +========================= + +Fixes since v2.11.3 +------------------- + + * "git cvsserver" no longer is invoked by "git daemon" by default, + as it is old and largely unmaintained. + + * Various Perl scripts did not use safe_pipe_capture() instead of + backticks, leaving them susceptible to end-user input. They have + been corrected. + +Credits go to joernchen <joernchen@phenoelit.de> for finding the +unsafe constructs in "git cvsserver", and to Jeff King at GitHub for +finding and fixing instances of the same issue in other scripts. + diff --git a/Documentation/RelNotes/2.12.5.txt b/Documentation/RelNotes/2.12.5.txt new file mode 100644 index 0000000000..8fa73cfce7 --- /dev/null +++ b/Documentation/RelNotes/2.12.5.txt @@ -0,0 +1,17 @@ +Git v2.12.5 Release Notes +========================= + +Fixes since v2.12.4 +------------------- + + * "git cvsserver" no longer is invoked by "git daemon" by default, + as it is old and largely unmaintained. + + * Various Perl scripts did not use safe_pipe_capture() instead of + backticks, leaving them susceptible to end-user input. They have + been corrected. + +Credits go to joernchen <joernchen@phenoelit.de> for finding the +unsafe constructs in "git cvsserver", and to Jeff King at GitHub for +finding and fixing instances of the same issue in other scripts. + diff --git a/Documentation/RelNotes/2.13.6.txt b/Documentation/RelNotes/2.13.6.txt new file mode 100644 index 0000000000..afcae9c808 --- /dev/null +++ b/Documentation/RelNotes/2.13.6.txt @@ -0,0 +1,17 @@ +Git v2.13.6 Release Notes +========================= + +Fixes since v2.13.5 +------------------- + + * "git cvsserver" no longer is invoked by "git daemon" by default, + as it is old and largely unmaintained. + + * Various Perl scripts did not use safe_pipe_capture() instead of + backticks, leaving them susceptible to end-user input. They have + been corrected. + +Credits go to joernchen <joernchen@phenoelit.de> for finding the +unsafe constructs in "git cvsserver", and to Jeff King at GitHub for +finding and fixing instances of the same issue in other scripts. + diff --git a/Documentation/RelNotes/2.14.2.txt b/Documentation/RelNotes/2.14.2.txt index bcfe78f59d..bec9186ade 100644 --- a/Documentation/RelNotes/2.14.2.txt +++ b/Documentation/RelNotes/2.14.2.txt @@ -91,4 +91,15 @@ Fixes since v2.14.1 * "git archive" did not work well with pathspecs and the export-ignore attribute. + * "git cvsserver" no longer is invoked by "git daemon" by default, + as it is old and largely unmaintained. + + * Various Perl scripts did not use safe_pipe_capture() instead of + backticks, leaving them susceptible to end-user input. They have + been corrected. + Also contains various documentation updates and code clean-ups. + +Credits go to joernchen <joernchen@phenoelit.de> for finding the +unsafe constructs in "git cvsserver", and to Jeff King at GitHub for +finding and fixing instances of the same issue in other scripts. diff --git a/Documentation/RelNotes/2.15.0.txt b/Documentation/RelNotes/2.15.0.txt index 290cad5287..7b8eeb52b6 100644 --- a/Documentation/RelNotes/2.15.0.txt +++ b/Documentation/RelNotes/2.15.0.txt @@ -8,12 +8,12 @@ Backward compatibility notes and other notable changes. more explicit '.' for that instead. The hope is that existing users will not mind this change, and eventually the warning can be turned into a hard error, upgrading the deprecation into removal of - this (mis)feature. That is now scheduled to happen in the upcoming - release. + this (mis)feature. That is now scheduled to happen in Git v2.16, + the next major release after this one. * Git now avoids blindly falling back to ".git" when the setup sequence said we are _not_ in Git repository. A corner case that - happens to work right now may be broken by a call to die("BUG"). + happens to work right now may be broken by a call to BUG(). We've tried hard to locate such cases and fixed them, but there might still be cases that need to be addressed--bug reports are greatly appreciated. @@ -61,6 +61,10 @@ UI, Workflows & Features other options to make it easier for scripts to grab existing trailer lines from a commit log message. + * The "--format=%(trailers)" option "git log" and its friends take + learned to take the 'unfold' and 'only' modifiers to normalize its + output, e.g. "git log --format=%(trailers:only,unfold)". + * "gitweb" shows a link to visit the 'raw' contents of blbos in the history overview page. @@ -84,6 +88,17 @@ UI, Workflows & Features used in a way similar to existing "--is-bare-repository" and friends. + * "git describe --match <pattern>" has been taught to play well with + the "--all" option. + + * "git branch" learned "-c/-C" to create a new branch by copying an + existing one. + + * Some commands (most notably "git status") makes an opportunistic + update when performing a read-only operation to help optimize later + operations in the same repository. The new "--no-optional-locks" + option can be passed to Git to disable them. + Performance, Internal Implementation, Development Support etc. @@ -189,6 +204,32 @@ Performance, Internal Implementation, Development Support etc. expect failures under a limited stack situation. This has been fixed. + * Many codepaths have been updated to squelch -Wimplicit-fallthrough + warnings from Gcc 7 (which is a good code hygiene). + + * Add a helper for DLL loading in anticipation for its need in a + future topic RSN. + + * "git status --ignored", when noticing that a directory without any + tracked path is ignored, still enumerated all the ignored paths in + the directory, which is unnecessary. The codepath has been + optimized to avoid this overhead. + + * The final batch to "git rebase -i" updates to move more code from + the shell script to C has been merged. + + * Operations that do not touch (majority of) packed refs have been + optimized by making accesses to packed-refs file lazy; we no longer + pre-parse everything, and an access to a single ref in the + packed-refs does not touch majority of irrelevant refs, either. + + * Add comment to clarify that the style file is meant to be used with + clang-5 and the rules are still work in progress. + + * Many variables that points at a region of memory that will live + throughout the life of the program have been marked with UNLEAK + marker to help the leak checkers concentrate on real leaks.. + Also contains various documentation updates and code clean-ups. @@ -359,6 +400,91 @@ Fixes since v2.14 alternate object stores overrun the end of the string. (merge f0f7bebef7 jk/info-alternates-fix later to maint). + * "git describe --match" learned to take multiple patterns in v2.13 + series, but the feature ignored the patterns after the first one + and did not work at all. This has been fixed. + (merge da769d2986 jk/describe-omit-some-refs later to maint). + + * "git filter-branch" cannot reproduce a history with a tag without + the tagger field, which only ancient versions of Git allowed to be + created. This has been corrected. + (merge b2c1ca6b4b ic/fix-filter-branch-to-handle-tag-without-tagger later to maint). + + * "git cat-file --textconv" started segfaulting recently, which + has been corrected. + (merge cc0ea7c9e5 jk/diff-blob later to maint). + + * The built-in pattern to detect the "function header" for HTML did + not match <H1>..<H6> elements without any attributes, which has + been fixed. + (merge 9c03caca2c ik/userdiff-html-h-element-fix later to maint). + + * "git mailinfo" was loose in decoding quoted printable and produced + garbage when the two letters after the equal sign are not + hexadecimal. This has been fixed. + (merge c8cf423eab rs/mailinfo-qp-decode-fix later to maint). + + * The machinery to create xdelta used in pack files received the + sizes of the data in size_t, but lost the higher bits of them by + storing them in "unsigned int" during the computation, which is + fixed. + + * The delta format used in the packfile cannot reference data at + offset larger than what can be expressed in 4-byte, but the + generator for the data failed to make sure the offset does not + overflow. This has been corrected. + + * The documentation for '-X<option>' for merges was misleadingly + written to suggest that "-s theirs" exists, which is not the case. + (merge c25d98b2a7 jc/merge-x-theirs-docfix later to maint). + + * "git fast-export" with -M/-C option issued "copy" instruction on a + path that is simultaneously modified, which was incorrect. + (merge b3e8ca89cf jt/fast-export-copy-modify-fix later to maint). + + * Many codepaths have been updated to squelch -Wsign-compare + warnings. + (merge 071bcaab64 rj/no-sign-compare later to maint). + + * Memory leaks in various codepaths have been plugged. + (merge 4d01a7fa65 ma/leakplugs later to maint). + + * Recent versions of "git rev-parse --parseopt" did not parse the + option specification that does not have the optional flags (*=?!) + correctly, which has been corrected. + (merge a6304fa4c2 bc/rev-parse-parseopt-fix later to maint). + + * The checkpoint command "git fast-import" did not flush updates to + refs and marks unless at least one object was created since the + last checkpoint, which has been corrected, as these things can + happen without any new object getting created. + (merge 30e215a65c er/fast-import-dump-refs-on-checkpoint later to maint). + + * Spell the name of our system as "Git" in the output from + request-pull script. + (merge e66d7c37a5 ar/request-pull-phrasofix later to maint). + + * Fixes for a handful memory access issues identified by valgrind. + (merge 2944a94c6b tg/memfixes later to maint). + + * Backports a moral equivalent of 2015 fix to the poll() emulation + from the upstream gnulib to fix occasional breakages on HPE NonStop. + (merge 61b2a1acaa rb/compat-poll-fix later to maint). + + * Users with "color.ui = always" in their configuration were broken + by a recent change that made plumbing commands to pay attention to + them as the patch created internally by "git add -p" were colored + (heh) and made unusable. Fix this regression by redefining + 'always' to mean the same thing as 'auto'. + (merge 6be4595edb jk/ui-color-always-to-auto-maint later to maint). + + * In the "--format=..." option of the "git for-each-ref" command (and + its friends, i.e. the listing mode of "git branch/tag"), "%(atom:)" + (e.g. "%(refname:)", "%(body:)" used to error out. Instead, treat + them as if the colon and an empty string that follows it were not + there. + (merge bea4dbeafd tb/ref-filter-empty-modifier later to maint). + * Other minor doc, test and build updates and code cleanups. (merge f094b89a4d ma/parse-maybe-bool later to maint). (merge 39b00fa4d4 jk/drop-sha1-entry-pos later to maint). @@ -376,3 +502,17 @@ Fixes since v2.14 (merge f7a32dd97f kd/doc-for-each-ref later to maint). (merge be94568bc7 ez/doc-duplicated-words-fix later to maint). (merge 01e4be6c3d ks/test-readme-phrasofix later to maint). + (merge 217bb56d4f hn/typofix later to maint). + (merge c08fd6388c jk/doc-read-tree-table-asciidoctor-fix later to maint). + (merge c3342b362e ks/doc-use-camelcase-for-config-name later to maint). + (merge 0bca165fdb jk/validate-headref-fix later to maint). + (merge 93dbefb389 mr/doc-negative-pathspec later to maint). + (merge 5e633326e4 ad/doc-markup-fix later to maint). + (merge 9ca356fa8b rs/cocci-de-paren-call-params later to maint). + (merge 7099153e8d rs/tag-null-pointer-arith-fix later to maint). + (merge 0e187d758c rs/run-command-use-alloc-array later to maint). + (merge e0222159fa jn/strbuf-doc-re-reuse later to maint). + (merge 97487ea11a rs/qsort-s later to maint). + (merge a9155c50bd sb/branch-avoid-repeated-strbuf-release later to maint). + (merge f777623514 ks/branch-tweak-error-message-for-extra-args later to maint). + (merge 33f3c683ec ks/verify-filename-non-option-error-message-tweak later to maint). diff --git a/Documentation/config.txt b/Documentation/config.txt index dc4e3f58a2..b53c994d0a 100644 --- a/Documentation/config.txt +++ b/Documentation/config.txt @@ -1058,10 +1058,10 @@ clean.requireForce:: color.branch:: A boolean to enable/disable color in the output of - linkgit:git-branch[1]. May be set to `always`, - `false` (or `never`) or `auto` (or `true`), in which case colors are used - only when the output is to a terminal. If unset, then the - value of `color.ui` is used (`auto` by default). + linkgit:git-branch[1]. May be set to `false` (or `never`) to + disable color entirely, `auto` (or `true` or `always`) in which + case colors are used only when the output is to a terminal. If + unset, then the value of `color.ui` is used (`auto` by default). color.branch.<slot>:: Use customized color for branch coloration. `<slot>` is one of @@ -1072,12 +1072,11 @@ color.branch.<slot>:: color.diff:: Whether to use ANSI escape sequences to add color to patches. - If this is set to `always`, linkgit:git-diff[1], + If this is set to `true` or `auto`, linkgit:git-diff[1], linkgit:git-log[1], and linkgit:git-show[1] will use color - for all patches. If it is set to `true` or `auto`, those - commands will only use color when output is to the terminal. - If unset, then the value of `color.ui` is used (`auto` by - default). + when output is to the terminal. The value `always` is a + historical synonym for `auto`. If unset, then the value of + `color.ui` is used (`auto` by default). + This does not affect linkgit:git-format-patch[1] or the 'git-diff-{asterisk}' plumbing commands. Can be overridden on the @@ -1141,12 +1140,12 @@ color.grep.<slot>:: -- color.interactive:: - When set to `always`, always use colors for interactive prompts + When set to `true` or `auto`, use colors for interactive prompts and displays (such as those used by "git-add --interactive" and - "git-clean --interactive"). When false (or `never`), never. - When set to `true` or `auto`, use colors only when the output is - to the terminal. If unset, then the value of `color.ui` is - used (`auto` by default). + "git-clean --interactive") when the output is to the terminal. + When false (or `never`), never show colors. The value `always` + is a historical synonym for `auto`. If unset, then the value of + `color.ui` is used (`auto` by default). color.interactive.<slot>:: Use customized color for 'git add --interactive' and 'git clean @@ -1193,10 +1192,10 @@ color.ui:: configuration to set a default for the `--color` option. Set it to `false` or `never` if you prefer Git commands not to use color unless enabled explicitly with some other configuration - or the `--color` option. Set it to `always` if you want all - output not intended for machine consumption to use color, to - `true` or `auto` (this is the default since Git 1.8.4) if you - want such output to use color when written to the terminal. + or the `--color` option. Set it to `true` or `auto` to enable + color when output is written to the terminal (this is also the + default since Git 1.8.4). The value `always` is a historical + synonym for `auto`. column.ui:: Specify whether supported commands should output in columns. @@ -3085,10 +3084,14 @@ submodule.<name>.url:: See linkgit:git-submodule[1] and linkgit:gitmodules[5] for details. submodule.<name>.update:: - The default update procedure for a submodule. This variable - is populated by `git submodule init` from the - linkgit:gitmodules[5] file. See description of 'update' - command in linkgit:git-submodule[1]. + The method by which a submodule is updated by 'git submodule update', + which is the only affected command, others such as + 'git checkout --recurse-submodules' are unaffected. It exists for + historical reasons, when 'git submodule' was the only command to + interact with submodules; settings like `submodule.active` + and `pull.rebase` are more specific. It is populated by + `git submodule init` from the linkgit:gitmodules[5] file. + See description of 'update' command in linkgit:git-submodule[1]. submodule.<name>.branch:: The remote branch name for a submodule, used by `git submodule diff --git a/Documentation/git-add.txt b/Documentation/git-add.txt index f4169fb1ec..b700beaff5 100644 --- a/Documentation/git-add.txt +++ b/Documentation/git-add.txt @@ -61,6 +61,9 @@ OPTIONS the working tree. Note that older versions of Git used to ignore removed files; use `--no-all` option if you want to add modified or new files but ignore removed ones. ++ +For more details about the <pathspec> syntax, see the 'pathspec' entry +in linkgit:gitglossary[7]. -n:: --dry-run:: diff --git a/Documentation/git-branch.txt b/Documentation/git-branch.txt index e292737b9c..fe029ac6fc 100644 --- a/Documentation/git-branch.txt +++ b/Documentation/git-branch.txt @@ -18,6 +18,7 @@ SYNOPSIS 'git branch' (--set-upstream-to=<upstream> | -u <upstream>) [<branchname>] 'git branch' --unset-upstream [<branchname>] 'git branch' (-m | -M) [<oldbranch>] <newbranch> +'git branch' (-c | -C) [<oldbranch>] <newbranch> 'git branch' (-d | -D) [-r] <branchname>... 'git branch' --edit-description [<branchname>] @@ -64,6 +65,10 @@ If <oldbranch> had a corresponding reflog, it is renamed to match renaming. If <newbranch> exists, -M must be used to force the rename to happen. +The `-c` and `-C` options have the exact same semantics as `-m` and +`-M`, except instead of the branch being renamed it along with its +config and reflog will be copied to a new name. + With a `-d` or `-D` option, `<branchname>` will be deleted. You may specify more than one branch for deletion. If the branch currently has a reflog then the reflog will also be deleted. @@ -92,10 +97,10 @@ OPTIONS all changes made to the branch ref, enabling use of date based sha1 expressions such as "<branchname>@\{yesterday}". Note that in non-bare repositories, reflogs are usually - enabled by default by the `core.logallrefupdates` config option. + enabled by default by the `core.logAllRefUpdates` config option. The negated form `--no-create-reflog` only overrides an earlier `--create-reflog`, but currently does not negate the setting of - `core.logallrefupdates`. + `core.logAllRefUpdates`. -f:: --force:: @@ -104,7 +109,7 @@ OPTIONS In combination with `-d` (or `--delete`), allow deleting the branch irrespective of its merged status. In combination with `-m` (or `--move`), allow renaming the branch even if the new - branch name already exists. + branch name already exists, the same applies for `-c` (or `--copy`). -m:: --move:: @@ -113,6 +118,13 @@ OPTIONS -M:: Shortcut for `--move --force`. +-c:: +--copy:: + Copy a branch and the corresponding reflog. + +-C:: + Shortcut for `--copy --force`. + --color[=<when>]:: Color branches to highlight current, local, and remote-tracking branches. diff --git a/Documentation/git-describe.txt b/Documentation/git-describe.txt index 26f19d3b07..c924c945ba 100644 --- a/Documentation/git-describe.txt +++ b/Documentation/git-describe.txt @@ -87,19 +87,23 @@ OPTIONS --match <pattern>:: Only consider tags matching the given `glob(7)` pattern, - excluding the "refs/tags/" prefix. This can be used to avoid - leaking private tags from the repository. If given multiple times, a - list of patterns will be accumulated, and tags matching any of the - patterns will be considered. Use `--no-match` to clear and reset the - list of patterns. + excluding the "refs/tags/" prefix. If used with `--all`, it also + considers local branches and remote-tracking references matching the + pattern, excluding respectively "refs/heads/" and "refs/remotes/" + prefix; references of other types are never considered. If given + multiple times, a list of patterns will be accumulated, and tags + matching any of the patterns will be considered. Use `--no-match` to + clear and reset the list of patterns. --exclude <pattern>:: Do not consider tags matching the given `glob(7)` pattern, excluding - the "refs/tags/" prefix. This can be used to narrow the tag space and - find only tags matching some meaningful criteria. If given multiple - times, a list of patterns will be accumulated and tags matching any - of the patterns will be excluded. When combined with --match a tag will - be considered when it matches at least one --match pattern and does not + the "refs/tags/" prefix. If used with `--all`, it also does not consider + local branches and remote-tracking references matching the pattern, + excluding respectively "refs/heads/" and "refs/remotes/" prefix; + references of other types are never considered. If given multiple times, + a list of patterns will be accumulated and tags matching any of the + patterns will be excluded. When combined with --match a tag will be + considered when it matches at least one --match pattern and does not match any of the --exclude patterns. Use `--no-exclude` to clear and reset the list of patterns. diff --git a/Documentation/git-filter-branch.txt b/Documentation/git-filter-branch.txt index 9e5169aa64..bebdcdec5a 100644 --- a/Documentation/git-filter-branch.txt +++ b/Documentation/git-filter-branch.txt @@ -14,7 +14,7 @@ SYNOPSIS [--commit-filter <command>] [--tag-name-filter <command>] [--subdirectory-filter <directory>] [--prune-empty] [--original <namespace>] [-d <directory>] [-f | --force] - [--] [<rev-list options>...] + [--state-branch <branch>] [--] [<rev-list options>...] DESCRIPTION ----------- @@ -198,6 +198,12 @@ to other tags will be rewritten to point to the underlying commit. directory or when there are already refs starting with 'refs/original/', unless forced. +--state-branch <branch>:: + This option will cause the mapping from old to new objects to + be loaded from named branch upon startup and saved as a new + commit to that branch upon exit, enabling incremental of large + trees. If '<branch>' does not exist it will be created. + <rev-list options>...:: Arguments for 'git rev-list'. All positive refs included by these options are rewritten. You may also specify options diff --git a/Documentation/git-for-each-ref.txt b/Documentation/git-for-each-ref.txt index 66b4e0a405..1d420e4cde 100644 --- a/Documentation/git-for-each-ref.txt +++ b/Documentation/git-for-each-ref.txt @@ -57,6 +57,11 @@ OPTIONS `xx`; for example `%00` interpolates to `\0` (NUL), `%09` to `\t` (TAB) and `%0a` to `\n` (LF). +--color[=<when>]: + Respect any colors specified in the `--format` option. The + `<when>` field must be one of `always`, `never`, or `auto` (if + `<when>` is absent, behave as if `always` was given). + --shell:: --perl:: --python:: @@ -213,11 +218,15 @@ and `date` to extract the named component. The complete message in a commit and tag object is `contents`. Its first line is `contents:subject`, where subject is the concatenation of all lines of the commit message up to the first blank line. The next -line is 'contents:body', where body is all of the lines after the first +line is `contents:body`, where body is all of the lines after the first blank line. The optional GPG signature is `contents:signature`. The first `N` lines of the message is obtained using `contents:lines=N`. Additionally, the trailers as interpreted by linkgit:git-interpret-trailers[1] -are obtained as 'contents:trailers'. +are obtained as `trailers` (or by using the historical alias +`contents:trailers`). Non-trailer lines from the trailer block can be omitted +with `trailers:only`. Whitespace-continuations can be removed from trailers so +that each trailer appears on a line by itself with its full content with +`trailers:unfold`. Both can be used together as `trailers:unfold,only`. For sorting purposes, fields with numeric values sort in numeric order (`objectsize`, `authordate`, `committerdate`, `creatordate`, `taggerdate`). diff --git a/Documentation/git-grep.txt b/Documentation/git-grep.txt index 720c7850e2..18b494731f 100644 --- a/Documentation/git-grep.txt +++ b/Documentation/git-grep.txt @@ -289,6 +289,9 @@ providing this option will cause it to die. <pathspec>...:: If given, limit the search to paths matching at least one pattern. Both leading paths match and glob(7) patterns are supported. ++ +For more details about the <pathspec> syntax, see the 'pathspec' entry +in linkgit:gitglossary[7]. Examples -------- @@ -305,6 +308,9 @@ Examples Looks for a line that has `NODE` or `Unexpected` in files that have lines that match both. +`git grep solution -- :^Documentation`:: + Looks for `solution`, excluding files in `Documentation`. + GIT --- Part of the linkgit:git[1] suite diff --git a/Documentation/git-read-tree.txt b/Documentation/git-read-tree.txt index 02576d8c0a..72bd809fb8 100644 --- a/Documentation/git-read-tree.txt +++ b/Documentation/git-read-tree.txt @@ -179,6 +179,7 @@ Here are the "carry forward" rules, where "I" denotes the index, "clean" means that index and work tree coincide, and "exists"/"nothing" refer to the presence of a path in the specified commit: +.... I H M Result ------------------------------------------------------- 0 nothing nothing nothing (does not happen) @@ -217,6 +218,7 @@ refer to the presence of a path in the specified commit: 19 no no yes exists exists keep index 20 yes yes no exists exists use M 21 no yes no exists exists fail +.... In all "keep index" cases, the index entry stays as in the original index file. If the entry is not up to date, diff --git a/Documentation/git-rebase.txt b/Documentation/git-rebase.txt index 6805a74aec..3cedfb0fd2 100644 --- a/Documentation/git-rebase.txt +++ b/Documentation/git-rebase.txt @@ -430,13 +430,15 @@ without an explicit `--interactive`. --autosquash:: --no-autosquash:: When the commit log message begins with "squash! ..." (or - "fixup! ..."), and there is a commit whose title begins with - the same ..., automatically modify the todo list of rebase -i - so that the commit marked for squashing comes right after the - commit to be modified, and change the action of the moved - commit from `pick` to `squash` (or `fixup`). Ignores subsequent - "fixup! " or "squash! " after the first, in case you referred to an - earlier fixup/squash with `git commit --fixup/--squash`. + "fixup! ..."), and there is already a commit in the todo list that + matches the same `...`, automatically modify the todo list of rebase + -i so that the commit marked for squashing comes right after the + commit to be modified, and change the action of the moved commit + from `pick` to `squash` (or `fixup`). A commit matches the `...` if + the commit subject matches, or if the `...` refers to the commit's + hash. As a fall-back, partial matches of the commit subject work, + too. The recommended way to create fixup/squash commits is by using + the `--fixup`/`--squash` options of linkgit:git-commit[1]. + This option is only valid when the `--interactive` option is used. + diff --git a/Documentation/git-shell.txt b/Documentation/git-shell.txt index 2e30a3e42d..54cf2560be 100644 --- a/Documentation/git-shell.txt +++ b/Documentation/git-shell.txt @@ -79,6 +79,22 @@ EOF $ chmod +x $HOME/git-shell-commands/no-interactive-login ---------------- +To enable git-cvsserver access (which should generally have the +`no-interactive-login` example above as a prerequisite, as creating +the git-shell-commands directory allows interactive logins): + +---------------- +$ cat >$HOME/git-shell-commands/cvs <<\EOF +if ! test $# = 1 && test "$1" = "server" +then + echo >&2 "git-cvsserver only handles \"server\"" + exit 1 +fi +exec git cvsserver server +EOF +$ chmod +x $HOME/git-shell-commands/cvs +---------------- + SEE ALSO -------- ssh(1), diff --git a/Documentation/git-status.txt b/Documentation/git-status.txt index d47f198f15..9f3a78a36c 100644 --- a/Documentation/git-status.txt +++ b/Documentation/git-status.txt @@ -111,6 +111,8 @@ configuration variable documented in linkgit:git-config[1]. without options are equivalent to 'always' and 'never' respectively. +<pathspec>...:: + See the 'pathspec' entry in linkgit:gitglossary[7]. OUTPUT ------ diff --git a/Documentation/git-tag.txt b/Documentation/git-tag.txt index 543fb425ee..956fc019f9 100644 --- a/Documentation/git-tag.txt +++ b/Documentation/git-tag.txt @@ -115,6 +115,11 @@ options for details. variable if it exists, or lexicographic order otherwise. See linkgit:git-config[1]. +--color[=<when>]: + Respect any colors specified in the `--format` option. The + `<when>` field must be one of `always`, `never`, or `auto` (if + `<when>` is absent, behave as if `always` was given). + -i:: --ignore-case:: Sorting and filtering tags are case insensitive. @@ -174,7 +179,7 @@ This option is only applicable when listing tags without annotation lines. `core.logAllRefUpdates` in linkgit:git-config[1]. The negated form `--no-create-reflog` only overrides an earlier `--create-reflog`, but currently does not negate the setting of - `core.logallrefupdates`. + `core.logAllRefUpdates`. <tagname>:: The name of the tag to create, delete, or describe. diff --git a/Documentation/git.txt b/Documentation/git.txt index 6e3a6767e5..7a1d629ca0 100644 --- a/Documentation/git.txt +++ b/Documentation/git.txt @@ -75,7 +75,7 @@ example the following invocations are equivalent: Note that omitting the `=` in `git -c foo.bar ...` is allowed and sets `foo.bar` to the boolean true value (just like `[foo]bar` would in a config file). Including the equals but with an empty value (like `git -c -foo.bar= ...`) sets `foo.bar` to the empty string which ` git config +foo.bar= ...`) sets `foo.bar` to the empty string which `git config --bool` will convert to `false`. --exec-path[=<path>]:: @@ -159,6 +159,10 @@ foo.bar= ...`) sets `foo.bar` to the empty string which ` git config Add "icase" magic to all pathspec. This is equivalent to setting the `GIT_ICASE_PATHSPECS` environment variable to `1`. +--no-optional-locks:: + Do not perform optional operations that require locks. This is + equivalent to setting the `GIT_OPTIONAL_LOCKS` to `0`. + GIT COMMANDS ------------ @@ -697,6 +701,14 @@ of clones and fetches. which feed potentially-untrusted URLS to git commands. See linkgit:git-config[1] for more details. +`GIT_OPTIONAL_LOCKS`:: + If set to `0`, Git will complete any requested operation without + performing any optional sub-operations that require taking a lock. + For example, this will prevent `git status` from refreshing the + index as a side effect. This is useful for processes running in + the background which do not want to cause lock contention with + other operations on the repository. Defaults to `1`. + Discussion[[Discussion]] ------------------------ diff --git a/Documentation/githooks.txt b/Documentation/githooks.txt index 1bb4f92d4d..5d3f45560e 100644 --- a/Documentation/githooks.txt +++ b/Documentation/githooks.txt @@ -127,11 +127,10 @@ help message found in the commented portion of the commit template. commit-msg ~~~~~~~~~~ -This hook is invoked by 'git commit', and can be bypassed -with the `--no-verify` option. It takes a single parameter, the -name of the file that holds the proposed commit log message. -Exiting with a non-zero status causes the 'git commit' to -abort. +This hook is invoked by 'git commit' and 'git merge', and can be +bypassed with the `--no-verify` option. It takes a single parameter, +the name of the file that holds the proposed commit log message. +Exiting with a non-zero status causes the command to abort. The hook is allowed to edit the message file in place, and can be used to normalize the message into some project standard format. It diff --git a/Documentation/glossary-content.txt b/Documentation/glossary-content.txt index b71b943b12..6b8888d123 100644 --- a/Documentation/glossary-content.txt +++ b/Documentation/glossary-content.txt @@ -407,7 +407,7 @@ these forms: exclude;; After a path matches any non-exclude pathspec, it will be run - through all exclude pathspec (magic signature: `!` or its + through all exclude pathspecs (magic signature: `!` or its synonym `^`). If it matches, the path is ignored. When there is no non-exclude pathspec, the exclusion is applied to the result set as if invoked without any pathspec. diff --git a/Documentation/merge-strategies.txt b/Documentation/merge-strategies.txt index 2eb92b9327..a09d597463 100644 --- a/Documentation/merge-strategies.txt +++ b/Documentation/merge-strategies.txt @@ -39,7 +39,8 @@ even look at what the other tree contains at all. It discards everything the other tree did, declaring 'our' history contains all that happened in it. theirs;; - This is the opposite of 'ours'. + This is the opposite of 'ours'; note that, unlike 'ours', there is + no 'theirs' merge stragegy to confuse this merge option with. patience;; With this option, 'merge-recursive' spends a little extra time diff --git a/Documentation/technical/hash-function-transition.txt b/Documentation/technical/hash-function-transition.txt new file mode 100644 index 0000000000..417ba491d0 --- /dev/null +++ b/Documentation/technical/hash-function-transition.txt @@ -0,0 +1,797 @@ +Git hash function transition +============================ + +Objective +--------- +Migrate Git from SHA-1 to a stronger hash function. + +Background +---------- +At its core, the Git version control system is a content addressable +filesystem. It uses the SHA-1 hash function to name content. For +example, files, directories, and revisions are referred to by hash +values unlike in other traditional version control systems where files +or versions are referred to via sequential numbers. The use of a hash +function to address its content delivers a few advantages: + +* Integrity checking is easy. Bit flips, for example, are easily + detected, as the hash of corrupted content does not match its name. +* Lookup of objects is fast. + +Using a cryptographically secure hash function brings additional +advantages: + +* Object names can be signed and third parties can trust the hash to + address the signed object and all objects it references. +* Communication using Git protocol and out of band communication + methods have a short reliable string that can be used to reliably + address stored content. + +Over time some flaws in SHA-1 have been discovered by security +researchers. https://shattered.io demonstrated a practical SHA-1 hash +collision. As a result, SHA-1 cannot be considered cryptographically +secure any more. This impacts the communication of hash values because +we cannot trust that a given hash value represents the known good +version of content that the speaker intended. + +SHA-1 still possesses the other properties such as fast object lookup +and safe error checking, but other hash functions are equally suitable +that are believed to be cryptographically secure. + +Goals +----- +Where NewHash is a strong 256-bit hash function to replace SHA-1 (see +"Selection of a New Hash", below): + +1. The transition to NewHash can be done one local repository at a time. + a. Requiring no action by any other party. + b. A NewHash repository can communicate with SHA-1 Git servers + (push/fetch). + c. Users can use SHA-1 and NewHash identifiers for objects + interchangeably (see "Object names on the command line", below). + d. New signed objects make use of a stronger hash function than + SHA-1 for their security guarantees. +2. Allow a complete transition away from SHA-1. + a. Local metadata for SHA-1 compatibility can be removed from a + repository if compatibility with SHA-1 is no longer needed. +3. Maintainability throughout the process. + a. The object format is kept simple and consistent. + b. Creation of a generalized repository conversion tool. + +Non-Goals +--------- +1. Add NewHash support to Git protocol. This is valuable and the + logical next step but it is out of scope for this initial design. +2. Transparently improving the security of existing SHA-1 signed + objects. +3. Intermixing objects using multiple hash functions in a single + repository. +4. Taking the opportunity to fix other bugs in Git's formats and + protocols. +5. Shallow clones and fetches into a NewHash repository. (This will + change when we add NewHash support to Git protocol.) +6. Skip fetching some submodules of a project into a NewHash + repository. (This also depends on NewHash support in Git + protocol.) + +Overview +-------- +We introduce a new repository format extension. Repositories with this +extension enabled use NewHash instead of SHA-1 to name their objects. +This affects both object names and object content --- both the names +of objects and all references to other objects within an object are +switched to the new hash function. + +NewHash repositories cannot be read by older versions of Git. + +Alongside the packfile, a NewHash repository stores a bidirectional +mapping between NewHash and SHA-1 object names. The mapping is generated +locally and can be verified using "git fsck". Object lookups use this +mapping to allow naming objects using either their SHA-1 and NewHash names +interchangeably. + +"git cat-file" and "git hash-object" gain options to display an object +in its sha1 form and write an object given its sha1 form. This +requires all objects referenced by that object to be present in the +object database so that they can be named using the appropriate name +(using the bidirectional hash mapping). + +Fetches from a SHA-1 based server convert the fetched objects into +NewHash form and record the mapping in the bidirectional mapping table +(see below for details). Pushes to a SHA-1 based server convert the +objects being pushed into sha1 form so the server does not have to be +aware of the hash function the client is using. + +Detailed Design +--------------- +Repository format extension +~~~~~~~~~~~~~~~~~~~~~~~~~~~ +A NewHash repository uses repository format version `1` (see +Documentation/technical/repository-version.txt) with extensions +`objectFormat` and `compatObjectFormat`: + + [core] + repositoryFormatVersion = 1 + [extensions] + objectFormat = newhash + compatObjectFormat = sha1 + +Specifying a repository format extension ensures that versions of Git +not aware of NewHash do not try to operate on these repositories, +instead producing an error message: + + $ git status + fatal: unknown repository extensions found: + objectformat + compatobjectformat + +See the "Transition plan" section below for more details on these +repository extensions. + +Object names +~~~~~~~~~~~~ +Objects can be named by their 40 hexadecimal digit sha1-name or 64 +hexadecimal digit newhash-name, plus names derived from those (see +gitrevisions(7)). + +The sha1-name of an object is the SHA-1 of the concatenation of its +type, length, a nul byte, and the object's sha1-content. This is the +traditional <sha1> used in Git to name objects. + +The newhash-name of an object is the NewHash of the concatenation of its +type, length, a nul byte, and the object's newhash-content. + +Object format +~~~~~~~~~~~~~ +The content as a byte sequence of a tag, commit, or tree object named +by sha1 and newhash differ because an object named by newhash-name refers to +other objects by their newhash-names and an object named by sha1-name +refers to other objects by their sha1-names. + +The newhash-content of an object is the same as its sha1-content, except +that objects referenced by the object are named using their newhash-names +instead of sha1-names. Because a blob object does not refer to any +other object, its sha1-content and newhash-content are the same. + +The format allows round-trip conversion between newhash-content and +sha1-content. + +Object storage +~~~~~~~~~~~~~~ +Loose objects use zlib compression and packed objects use the packed +format described in Documentation/technical/pack-format.txt, just like +today. The content that is compressed and stored uses newhash-content +instead of sha1-content. + +Pack index +~~~~~~~~~~ +Pack index (.idx) files use a new v3 format that supports multiple +hash functions. They have the following format (all integers are in +network byte order): + +- A header appears at the beginning and consists of the following: + - The 4-byte pack index signature: '\377t0c' + - 4-byte version number: 3 + - 4-byte length of the header section, including the signature and + version number + - 4-byte number of objects contained in the pack + - 4-byte number of object formats in this pack index: 2 + - For each object format: + - 4-byte format identifier (e.g., 'sha1' for SHA-1) + - 4-byte length in bytes of shortened object names. This is the + shortest possible length needed to make names in the shortened + object name table unambiguous. + - 4-byte integer, recording where tables relating to this format + are stored in this index file, as an offset from the beginning. + - 4-byte offset to the trailer from the beginning of this file. + - Zero or more additional key/value pairs (4-byte key, 4-byte + value). Only one key is supported: 'PSRC'. See the "Loose objects + and unreachable objects" section for supported values and how this + is used. All other keys are reserved. Readers must ignore + unrecognized keys. +- Zero or more NUL bytes. This can optionally be used to improve the + alignment of the full object name table below. +- Tables for the first object format: + - A sorted table of shortened object names. These are prefixes of + the names of all objects in this pack file, packed together + without offset values to reduce the cache footprint of the binary + search for a specific object name. + + - A table of full object names in pack order. This allows resolving + a reference to "the nth object in the pack file" (from a + reachability bitmap or from the next table of another object + format) to its object name. + + - A table of 4-byte values mapping object name order to pack order. + For an object in the table of sorted shortened object names, the + value at the corresponding index in this table is the index in the + previous table for that same object. + + This can be used to look up the object in reachability bitmaps or + to look up its name in another object format. + + - A table of 4-byte CRC32 values of the packed object data, in the + order that the objects appear in the pack file. This is to allow + compressed data to be copied directly from pack to pack during + repacking without undetected data corruption. + + - A table of 4-byte offset values. For an object in the table of + sorted shortened object names, the value at the corresponding + index in this table indicates where that object can be found in + the pack file. These are usually 31-bit pack file offsets, but + large offsets are encoded as an index into the next table with the + most significant bit set. + + - A table of 8-byte offset entries (empty for pack files less than + 2 GiB). Pack files are organized with heavily used objects toward + the front, so most object references should not need to refer to + this table. +- Zero or more NUL bytes. +- Tables for the second object format, with the same layout as above, + up to and not including the table of CRC32 values. +- Zero or more NUL bytes. +- The trailer consists of the following: + - A copy of the 20-byte NewHash checksum at the end of the + corresponding packfile. + + - 20-byte NewHash checksum of all of the above. + +Loose object index +~~~~~~~~~~~~~~~~~~ +A new file $GIT_OBJECT_DIR/loose-object-idx contains information about +all loose objects. Its format is + + # loose-object-idx + (newhash-name SP sha1-name LF)* + +where the object names are in hexadecimal format. The file is not +sorted. + +The loose object index is protected against concurrent writes by a +lock file $GIT_OBJECT_DIR/loose-object-idx.lock. To add a new loose +object: + +1. Write the loose object to a temporary file, like today. +2. Open loose-object-idx.lock with O_CREAT | O_EXCL to acquire the lock. +3. Rename the loose object into place. +4. Open loose-object-idx with O_APPEND and write the new object +5. Unlink loose-object-idx.lock to release the lock. + +To remove entries (e.g. in "git pack-refs" or "git-prune"): + +1. Open loose-object-idx.lock with O_CREAT | O_EXCL to acquire the + lock. +2. Write the new content to loose-object-idx.lock. +3. Unlink any loose objects being removed. +4. Rename to replace loose-object-idx, releasing the lock. + +Translation table +~~~~~~~~~~~~~~~~~ +The index files support a bidirectional mapping between sha1-names +and newhash-names. The lookup proceeds similarly to ordinary object +lookups. For example, to convert a sha1-name to a newhash-name: + + 1. Look for the object in idx files. If a match is present in the + idx's sorted list of truncated sha1-names, then: + a. Read the corresponding entry in the sha1-name order to pack + name order mapping. + b. Read the corresponding entry in the full sha1-name table to + verify we found the right object. If it is, then + c. Read the corresponding entry in the full newhash-name table. + That is the object's newhash-name. + 2. Check for a loose object. Read lines from loose-object-idx until + we find a match. + +Step (1) takes the same amount of time as an ordinary object lookup: +O(number of packs * log(objects per pack)). Step (2) takes O(number of +loose objects) time. To maintain good performance it will be necessary +to keep the number of loose objects low. See the "Loose objects and +unreachable objects" section below for more details. + +Since all operations that make new objects (e.g., "git commit") add +the new objects to the corresponding index, this mapping is possible +for all objects in the object store. + +Reading an object's sha1-content +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The sha1-content of an object can be read by converting all newhash-names +its newhash-content references to sha1-names using the translation table. + +Fetch +~~~~~ +Fetching from a SHA-1 based server requires translating between SHA-1 +and NewHash based representations on the fly. + +SHA-1s named in the ref advertisement that are present on the client +can be translated to NewHash and looked up as local objects using the +translation table. + +Negotiation proceeds as today. Any "have"s generated locally are +converted to SHA-1 before being sent to the server, and SHA-1s +mentioned by the server are converted to NewHash when looking them up +locally. + +After negotiation, the server sends a packfile containing the +requested objects. We convert the packfile to NewHash format using +the following steps: + +1. index-pack: inflate each object in the packfile and compute its + SHA-1. Objects can contain deltas in OBJ_REF_DELTA format against + objects the client has locally. These objects can be looked up + using the translation table and their sha1-content read as + described above to resolve the deltas. +2. topological sort: starting at the "want"s from the negotiation + phase, walk through objects in the pack and emit a list of them, + excluding blobs, in reverse topologically sorted order, with each + object coming later in the list than all objects it references. + (This list only contains objects reachable from the "wants". If the + pack from the server contained additional extraneous objects, then + they will be discarded.) +3. convert to newhash: open a new (newhash) packfile. Read the topologically + sorted list just generated. For each object, inflate its + sha1-content, convert to newhash-content, and write it to the newhash + pack. Record the new sha1<->newhash mapping entry for use in the idx. +4. sort: reorder entries in the new pack to match the order of objects + in the pack the server generated and include blobs. Write a newhash idx + file +5. clean up: remove the SHA-1 based pack file, index, and + topologically sorted list obtained from the server in steps 1 + and 2. + +Step 3 requires every object referenced by the new object to be in the +translation table. This is why the topological sort step is necessary. + +As an optimization, step 1 could write a file describing what non-blob +objects each object it has inflated from the packfile references. This +makes the topological sort in step 2 possible without inflating the +objects in the packfile for a second time. The objects need to be +inflated again in step 3, for a total of two inflations. + +Step 4 is probably necessary for good read-time performance. "git +pack-objects" on the server optimizes the pack file for good data +locality (see Documentation/technical/pack-heuristics.txt). + +Details of this process are likely to change. It will take some +experimenting to get this to perform well. + +Push +~~~~ +Push is simpler than fetch because the objects referenced by the +pushed objects are already in the translation table. The sha1-content +of each object being pushed can be read as described in the "Reading +an object's sha1-content" section to generate the pack written by git +send-pack. + +Signed Commits +~~~~~~~~~~~~~~ +We add a new field "gpgsig-newhash" to the commit object format to allow +signing commits without relying on SHA-1. It is similar to the +existing "gpgsig" field. Its signed payload is the newhash-content of the +commit object with any "gpgsig" and "gpgsig-newhash" fields removed. + +This means commits can be signed +1. using SHA-1 only, as in existing signed commit objects +2. using both SHA-1 and NewHash, by using both gpgsig-newhash and gpgsig + fields. +3. using only NewHash, by only using the gpgsig-newhash field. + +Old versions of "git verify-commit" can verify the gpgsig signature in +cases (1) and (2) without modifications and view case (3) as an +ordinary unsigned commit. + +Signed Tags +~~~~~~~~~~~ +We add a new field "gpgsig-newhash" to the tag object format to allow +signing tags without relying on SHA-1. Its signed payload is the +newhash-content of the tag with its gpgsig-newhash field and "-----BEGIN PGP +SIGNATURE-----" delimited in-body signature removed. + +This means tags can be signed +1. using SHA-1 only, as in existing signed tag objects +2. using both SHA-1 and NewHash, by using gpgsig-newhash and an in-body + signature. +3. using only NewHash, by only using the gpgsig-newhash field. + +Mergetag embedding +~~~~~~~~~~~~~~~~~~ +The mergetag field in the sha1-content of a commit contains the +sha1-content of a tag that was merged by that commit. + +The mergetag field in the newhash-content of the same commit contains the +newhash-content of the same tag. + +Submodules +~~~~~~~~~~ +To convert recorded submodule pointers, you need to have the converted +submodule repository in place. The translation table of the submodule +can be used to look up the new hash. + +Loose objects and unreachable objects +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Fast lookups in the loose-object-idx require that the number of loose +objects not grow too high. + +"git gc --auto" currently waits for there to be 6700 loose objects +present before consolidating them into a packfile. We will need to +measure to find a more appropriate threshold for it to use. + +"git gc --auto" currently waits for there to be 50 packs present +before combining packfiles. Packing loose objects more aggressively +may cause the number of pack files to grow too quickly. This can be +mitigated by using a strategy similar to Martin Fick's exponential +rolling garbage collection script: +https://gerrit-review.googlesource.com/c/gerrit/+/35215 + +"git gc" currently expels any unreachable objects it encounters in +pack files to loose objects in an attempt to prevent a race when +pruning them (in case another process is simultaneously writing a new +object that refers to the about-to-be-deleted object). This leads to +an explosion in the number of loose objects present and disk space +usage due to the objects in delta form being replaced with independent +loose objects. Worse, the race is still present for loose objects. + +Instead, "git gc" will need to move unreachable objects to a new +packfile marked as UNREACHABLE_GARBAGE (using the PSRC field; see +below). To avoid the race when writing new objects referring to an +about-to-be-deleted object, code paths that write new objects will +need to copy any objects from UNREACHABLE_GARBAGE packs that they +refer to to new, non-UNREACHABLE_GARBAGE packs (or loose objects). +UNREACHABLE_GARBAGE are then safe to delete if their creation time (as +indicated by the file's mtime) is long enough ago. + +To avoid a proliferation of UNREACHABLE_GARBAGE packs, they can be +combined under certain circumstances. If "gc.garbageTtl" is set to +greater than one day, then packs created within a single calendar day, +UTC, can be coalesced together. The resulting packfile would have an +mtime before midnight on that day, so this makes the effective maximum +ttl the garbageTtl + 1 day. If "gc.garbageTtl" is less than one day, +then we divide the calendar day into intervals one-third of that ttl +in duration. Packs created within the same interval can be coalesced +together. The resulting packfile would have an mtime before the end of +the interval, so this makes the effective maximum ttl equal to the +garbageTtl * 4/3. + +This rule comes from Thirumala Reddy Mutchukota's JGit change +https://git.eclipse.org/r/90465. + +The UNREACHABLE_GARBAGE setting goes in the PSRC field of the pack +index. More generally, that field indicates where a pack came from: + + - 1 (PACK_SOURCE_RECEIVE) for a pack received over the network + - 2 (PACK_SOURCE_AUTO) for a pack created by a lightweight + "gc --auto" operation + - 3 (PACK_SOURCE_GC) for a pack created by a full gc + - 4 (PACK_SOURCE_UNREACHABLE_GARBAGE) for potential garbage + discovered by gc + - 5 (PACK_SOURCE_INSERT) for locally created objects that were + written directly to a pack file, e.g. from "git add ." + +This information can be useful for debugging and for "gc --auto" to +make appropriate choices about which packs to coalesce. + +Caveats +------- +Invalid objects +~~~~~~~~~~~~~~~ +The conversion from sha1-content to newhash-content retains any +brokenness in the original object (e.g., tree entry modes encoded with +leading 0, tree objects whose paths are not sorted correctly, and +commit objects without an author or committer). This is a deliberate +feature of the design to allow the conversion to round-trip. + +More profoundly broken objects (e.g., a commit with a truncated "tree" +header line) cannot be converted but were not usable by current Git +anyway. + +Shallow clone and submodules +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Because it requires all referenced objects to be available in the +locally generated translation table, this design does not support +shallow clone or unfetched submodules. Protocol improvements might +allow lifting this restriction. + +Alternates +~~~~~~~~~~ +For the same reason, a newhash repository cannot borrow objects from a +sha1 repository using objects/info/alternates or +$GIT_ALTERNATE_OBJECT_REPOSITORIES. + +git notes +~~~~~~~~~ +The "git notes" tool annotates objects using their sha1-name as key. +This design does not describe a way to migrate notes trees to use +newhash-names. That migration is expected to happen separately (for +example using a file at the root of the notes tree to describe which +hash it uses). + +Server-side cost +~~~~~~~~~~~~~~~~ +Until Git protocol gains NewHash support, using NewHash based storage +on public-facing Git servers is strongly discouraged. Once Git +protocol gains NewHash support, NewHash based servers are likely not +to support SHA-1 compatibility, to avoid what may be a very expensive +hash reencode during clone and to encourage peers to modernize. + +The design described here allows fetches by SHA-1 clients of a +personal NewHash repository because it's not much more difficult than +allowing pushes from that repository. This support needs to be guarded +by a configuration option --- servers like git.kernel.org that serve a +large number of clients would not be expected to bear that cost. + +Meaning of signatures +~~~~~~~~~~~~~~~~~~~~~ +The signed payload for signed commits and tags does not explicitly +name the hash used to identify objects. If some day Git adopts a new +hash function with the same length as the current SHA-1 (40 +hexadecimal digit) or NewHash (64 hexadecimal digit) objects then the +intent behind the PGP signed payload in an object signature is +unclear: + + object e7e07d5a4fcc2a203d9873968ad3e6bd4d7419d7 + type commit + tag v2.12.0 + tagger Junio C Hamano <gitster@pobox.com> 1487962205 -0800 + + Git 2.12 + +Does this mean Git v2.12.0 is the commit with sha1-name +e7e07d5a4fcc2a203d9873968ad3e6bd4d7419d7 or the commit with +new-40-digit-hash-name e7e07d5a4fcc2a203d9873968ad3e6bd4d7419d7? + +Fortunately NewHash and SHA-1 have different lengths. If Git starts +using another hash with the same length to name objects, then it will +need to change the format of signed payloads using that hash to +address this issue. + +Object names on the command line +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +To support the transition (see Transition plan below), this design +supports four different modes of operation: + + 1. ("dark launch") Treat object names input by the user as SHA-1 and + convert any object names written to output to SHA-1, but store + objects using NewHash. This allows users to test the code with no + visible behavior change except for performance. This allows + allows running even tests that assume the SHA-1 hash function, to + sanity-check the behavior of the new mode. + + 2. ("early transition") Allow both SHA-1 and NewHash object names in + input. Any object names written to output use SHA-1. This allows + users to continue to make use of SHA-1 to communicate with peers + (e.g. by email) that have not migrated yet and prepares for mode 3. + + 3. ("late transition") Allow both SHA-1 and NewHash object names in + input. Any object names written to output use NewHash. In this + mode, users are using a more secure object naming method by + default. The disruption is minimal as long as most of their peers + are in mode 2 or mode 3. + + 4. ("post-transition") Treat object names input by the user as + NewHash and write output using NewHash. This is safer than mode 3 + because there is less risk that input is incorrectly interpreted + using the wrong hash function. + +The mode is specified in configuration. + +The user can also explicitly specify which format to use for a +particular revision specifier and for output, overriding the mode. For +example: + +git --output-format=sha1 log abac87a^{sha1}..f787cac^{newhash} + +Selection of a New Hash +----------------------- +In early 2005, around the time that Git was written, Xiaoyun Wang, +Yiqun Lisa Yin, and Hongbo Yu announced an attack finding SHA-1 +collisions in 2^69 operations. In August they published details. +Luckily, no practical demonstrations of a collision in full SHA-1 were +published until 10 years later, in 2017. + +The hash function NewHash to replace SHA-1 should be stronger than +SHA-1 was: we would like it to be trustworthy and useful in practice +for at least 10 years. + +Some other relevant properties: + +1. A 256-bit hash (long enough to match common security practice; not + excessively long to hurt performance and disk usage). + +2. High quality implementations should be widely available (e.g. in + OpenSSL). + +3. The hash function's properties should match Git's needs (e.g. Git + requires collision and 2nd preimage resistance and does not require + length extension resistance). + +4. As a tiebreaker, the hash should be fast to compute (fortunately + many contenders are faster than SHA-1). + +Some hashes under consideration are SHA-256, SHA-512/256, SHA-256x16, +K12, and BLAKE2bp-256. + +Transition plan +--------------- +Some initial steps can be implemented independently of one another: +- adding a hash function API (vtable) +- teaching fsck to tolerate the gpgsig-newhash field +- excluding gpgsig-* from the fields copied by "git commit --amend" +- annotating tests that depend on SHA-1 values with a SHA1 test + prerequisite +- using "struct object_id", GIT_MAX_RAWSZ, and GIT_MAX_HEXSZ + consistently instead of "unsigned char *" and the hardcoded + constants 20 and 40. +- introducing index v3 +- adding support for the PSRC field and safer object pruning + + +The first user-visible change is the introduction of the objectFormat +extension (without compatObjectFormat). This requires: +- implementing the loose-object-idx +- teaching fsck about this mode of operation +- using the hash function API (vtable) when computing object names +- signing objects and verifying signatures +- rejecting attempts to fetch from or push to an incompatible + repository + +Next comes introduction of compatObjectFormat: +- translating object names between object formats +- translating object content between object formats +- generating and verifying signatures in the compat format +- adding appropriate index entries when adding a new object to the + object store +- --output-format option +- ^{sha1} and ^{newhash} revision notation +- configuration to specify default input and output format (see + "Object names on the command line" above) + +The next step is supporting fetches and pushes to SHA-1 repositories: +- allow pushes to a repository using the compat format +- generate a topologically sorted list of the SHA-1 names of fetched + objects +- convert the fetched packfile to newhash format and generate an idx + file +- re-sort to match the order of objects in the fetched packfile + +The infrastructure supporting fetch also allows converting an existing +repository. In converted repositories and new clones, end users can +gain support for the new hash function without any visible change in +behavior (see "dark launch" in the "Object names on the command line" +section). In particular this allows users to verify NewHash signatures +on objects in the repository, and it should ensure the transition code +is stable in production in preparation for using it more widely. + +Over time projects would encourage their users to adopt the "early +transition" and then "late transition" modes to take advantage of the +new, more futureproof NewHash object names. + +When objectFormat and compatObjectFormat are both set, commands +generating signatures would generate both SHA-1 and NewHash signatures +by default to support both new and old users. + +In projects using NewHash heavily, users could be encouraged to adopt +the "post-transition" mode to avoid accidentally making implicit use +of SHA-1 object names. + +Once a critical mass of users have upgraded to a version of Git that +can verify NewHash signatures and have converted their existing +repositories to support verifying them, we can add support for a +setting to generate only NewHash signatures. This is expected to be at +least a year later. + +That is also a good moment to advertise the ability to convert +repositories to use NewHash only, stripping out all SHA-1 related +metadata. This improves performance by eliminating translation +overhead and security by avoiding the possibility of accidentally +relying on the safety of SHA-1. + +Updating Git's protocols to allow a server to specify which hash +functions it supports is also an important part of this transition. It +is not discussed in detail in this document but this transition plan +assumes it happens. :) + +Alternatives considered +----------------------- +Upgrading everyone working on a particular project on a flag day +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Projects like the Linux kernel are large and complex enough that +flipping the switch for all projects based on the repository at once +is infeasible. + +Not only would all developers and server operators supporting +developers have to switch on the same flag day, but supporting tooling +(continuous integration, code review, bug trackers, etc) would have to +be adapted as well. This also makes it difficult to get early feedback +from some project participants testing before it is time for mass +adoption. + +Using hash functions in parallel +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +(e.g. https://public-inbox.org/git/22708.8913.864049.452252@chiark.greenend.org.uk/ ) +Objects newly created would be addressed by the new hash, but inside +such an object (e.g. commit) it is still possible to address objects +using the old hash function. +* You cannot trust its history (needed for bisectability) in the + future without further work +* Maintenance burden as the number of supported hash functions grows + (they will never go away, so they accumulate). In this proposal, by + comparison, converted objects lose all references to SHA-1. + +Signed objects with multiple hashes +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Instead of introducing the gpgsig-newhash field in commit and tag objects +for newhash-content based signatures, an earlier version of this design +added "hash newhash <newhash-name>" fields to strengthen the existing +sha1-content based signatures. + +In other words, a single signature was used to attest to the object +content using both hash functions. This had some advantages: +* Using one signature instead of two speeds up the signing process. +* Having one signed payload with both hashes allows the signer to + attest to the sha1-name and newhash-name referring to the same object. +* All users consume the same signature. Broken signatures are likely + to be detected quickly using current versions of git. + +However, it also came with disadvantages: +* Verifying a signed object requires access to the sha1-names of all + objects it references, even after the transition is complete and + translation table is no longer needed for anything else. To support + this, the design added fields such as "hash sha1 tree <sha1-name>" + and "hash sha1 parent <sha1-name>" to the newhash-content of a signed + commit, complicating the conversion process. +* Allowing signed objects without a sha1 (for after the transition is + complete) complicated the design further, requiring a "nohash sha1" + field to suppress including "hash sha1" fields in the newhash-content + and signed payload. + +Lazily populated translation table +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Some of the work of building the translation table could be deferred to +push time, but that would significantly complicate and slow down pushes. +Calculating the sha1-name at object creation time at the same time it is +being streamed to disk and having its newhash-name calculated should be +an acceptable cost. + +Document History +---------------- + +2017-03-03 +bmwill@google.com, jonathantanmy@google.com, jrnieder@gmail.com, +sbeller@google.com + +Initial version sent to +http://public-inbox.org/git/20170304011251.GA26789@aiede.mtv.corp.google.com + +2017-03-03 jrnieder@gmail.com +Incorporated suggestions from jonathantanmy and sbeller: +* describe purpose of signed objects with each hash type +* redefine signed object verification using object content under the + first hash function + +2017-03-06 jrnieder@gmail.com +* Use SHA3-256 instead of SHA2 (thanks, Linus and brian m. carlson).[1][2] +* Make sha3-based signatures a separate field, avoiding the need for + "hash" and "nohash" fields (thanks to peff[3]). +* Add a sorting phase to fetch (thanks to Junio for noticing the need + for this). +* Omit blobs from the topological sort during fetch (thanks to peff). +* Discuss alternates, git notes, and git servers in the caveats + section (thanks to Junio Hamano, brian m. carlson[4], and Shawn + Pearce). +* Clarify language throughout (thanks to various commenters, + especially Junio). + +2017-09-27 jrnieder@gmail.com, sbeller@google.com +* use placeholder NewHash instead of SHA3-256 +* describe criteria for picking a hash function. +* include a transition plan (thanks especially to Brandon Williams + for fleshing these ideas out) +* define the translation table (thanks, Shawn Pearce[5], Jonathan + Tan, and Masaya Suzuki) +* avoid loose object overhead by packing more aggressively in + "git gc --auto" + +[1] http://public-inbox.org/git/CA+55aFzJtejiCjV0e43+9oR3QuJK2PiFiLQemytoLpyJWe6P9w@mail.gmail.com/ +[2] http://public-inbox.org/git/CA+55aFz+gkAsDZ24zmePQuEs1XPS9BP_s8O7Q4wQ7LV7X5-oDA@mail.gmail.com/ +[3] http://public-inbox.org/git/20170306084353.nrns455dvkdsfgo5@sigill.intra.peff.net/ +[4] http://public-inbox.org/git/20170304224936.rqqtkdvfjgyezsht@genre.crustytoothpaste.net +[5] https://public-inbox.org/git/CAJo=hJtoX9=AyLHHpUJS7fueV9ciZ_MNpnEPHUz8Whui6g9F0A@mail.gmail.com/ |