diff options
Diffstat (limited to 'Documentation/howto')
| -rw-r--r-- | Documentation/howto/keep-canonical-history-correct.txt | 216 | ||||
| -rw-r--r-- | Documentation/howto/maintain-git.txt | 18 | ||||
| -rw-r--r-- | Documentation/howto/new-command.txt | 6 | ||||
| -rw-r--r-- | Documentation/howto/rebase-from-internal-branch.txt | 2 | ||||
| -rw-r--r-- | Documentation/howto/recover-corrupted-object-harder.txt | 241 | ||||
| -rw-r--r-- | Documentation/howto/revert-a-faulty-merge.txt | 20 | ||||
| -rw-r--r-- | Documentation/howto/revert-branch-rebase.txt | 2 | ||||
| -rw-r--r-- | Documentation/howto/setup-git-server-over-http.txt | 2 |
8 files changed, 483 insertions, 24 deletions
diff --git a/Documentation/howto/keep-canonical-history-correct.txt b/Documentation/howto/keep-canonical-history-correct.txt new file mode 100644 index 0000000000..35d48ef714 --- /dev/null +++ b/Documentation/howto/keep-canonical-history-correct.txt @@ -0,0 +1,216 @@ +From: Junio C Hamano <gitster@pobox.com> +Date: Wed, 07 May 2014 13:15:39 -0700 +Subject: Beginner question on "Pull is mostly evil" +Abstract: This how-to explains a method for keeping a + project's history correct when using git pull. +Content-type: text/asciidoc + +Keep authoritative canonical history correct with git pull +========================================================== + +Sometimes a new project integrator will end up with project history +that appears to be "backwards" from what other project developers +expect. This howto presents a suggested integration workflow for +maintaining a central repository. + +Suppose that that central repository has this history: + +------------ + ---o---o---A +------------ + +which ends at commit `A` (time flows from left to right and each node +in the graph is a commit, lines between them indicating parent-child +relationship). + +Then you clone it and work on your own commits, which leads you to +have this history in *your* repository: + +------------ + ---o---o---A---B---C +------------ + +Imagine your coworker did the same and built on top of `A` in *his* +repository in the meantime, and then pushed it to the +central repository: + +------------ + ---o---o---A---X---Y---Z +------------ + +Now, if you `git push` at this point, because your history that leads +to `C` lacks `X`, `Y` and `Z`, it will fail. You need to somehow make +the tip of your history a descendant of `Z`. + +One suggested way to solve the problem is "fetch and then merge", aka +`git pull`. When you fetch, your repository will have a history like +this: + +------------ + ---o---o---A---B---C + \ + X---Y---Z +------------ + +Once you run merge after that, while still on *your* branch, i.e. `C`, +you will create a merge `M` and make the history look like this: + +------------ + ---o---o---A---B---C---M + \ / + X---Y---Z +------------ + +`M` is a descendant of `Z`, so you can push to update the central +repository. Such a merge `M` does not lose any commit in both +histories, so in that sense it may not be wrong, but when people want +to talk about "the authoritative canonical history that is shared +among the project participants", i.e. "the trunk", they often view +it as "commits you see by following the first-parent chain", and use +this command to view it: + +------------ + $ git log --first-parent +------------ + +For all other people who observed the central repository after your +coworker pushed `Z` but before you pushed `M`, the commit on the trunk +used to be `o-o-A-X-Y-Z`. But because you made `M` while you were on +`C`, `M`'s first parent is `C`, so by pushing `M` to advance the +central repository, you made `X-Y-Z` a side branch, not on the trunk. + +You would rather want to have a history of this shape: + +------------ + ---o---o---A---X---Y---Z---M' + \ / + B-----------C +------------ + +so that in the first-parent chain, it is clear that the project first +did `X` and then `Y` and then `Z` and merged a change that consists of +two commits `B` and `C` that achieves a single goal. You may have +worked on fixing the bug #12345 with these two patches, and the merge +`M'` with swapped parents can say in its log message "Merge +fix-bug-12345". Having a way to tell `git pull` to create a merge +but record the parents in reverse order may be a way to do so. + +Note that I said "achieves a single goal" above, because this is +important. "Swapping the merge order" only covers a special case +where the project does not care too much about having unrelated +things done on a single merge but cares a lot about first-parent +chain. + +There are multiple schools of thought about the "trunk" management. + + 1. Some projects want to keep a completely linear history without any + merges. Obviously, swapping the merge order would not match their + taste. You would need to flatten your history on top of the + updated upstream to result in a history of this shape instead: ++ +------------ + ---o---o---A---X---Y---Z---B---C +------------ ++ +with `git pull --rebase` or something. + + 2. Some projects tolerate merges in their history, but do not worry + too much about the first-parent order, and allow fast-forward + merges. To them, swapping the merge order does not hurt, but + it is unnecessary. + + 3. Some projects want each commit on the "trunk" to do one single + thing. The output of `git log --first-parent` in such a project + would show either a merge of a side branch that completes a single + theme, or a single commit that completes a single theme by itself. + If your two commits `B` and `C` (or they may even be two groups of + commits) were solving two independent issues, then the merge `M'` + we made in the earlier example by swapping the merge order is + still not up to the project standard. It merges two unrelated + efforts `B` and `C` at the same time. + +For projects in the last category (Git itself is one of them), +individual developers would want to prepare a history more like +this: + +------------ + C0--C1--C2 topic-c + / + ---o---o---A master + \ + B0--B1--B2 topic-b +------------ + +That is, keeping separate topics on separate branches, perhaps like +so: + +------------ + $ git clone $URL work && cd work + $ git checkout -b topic-b master + $ ... work to create B0, B1 and B2 to complete one theme + $ git checkout -b topic-c master + $ ... same for the theme of topic-c +------------ + +And then + +------------ + $ git checkout master + $ git pull --ff-only +------------ + +would grab `X`, `Y` and `Z` from the upstream and advance your master +branch: + +------------ + C0--C1--C2 topic-c + / + ---o---o---A---X---Y---Z master + \ + B0--B1--B2 topic-b +------------ + +And then you would merge these two branches separately: + +------------ + $ git merge topic-b + $ git merge topic-c +------------ + +to result in + +------------ + C0--C1---------C2 + / \ + ---o---o---A---X---Y---Z---M---N + \ / + B0--B1-----B2 +------------ + +and push it back to the central repository. + +It is very much possible that while you are merging topic-b and +topic-c, somebody again advanced the history in the central repository +to put `W` on top of `Z`, and make your `git push` fail. + +In such a case, you would rewind to discard `M` and `N`, update the +tip of your 'master' again and redo the two merges: + +------------ + $ git reset --hard origin/master + $ git pull --ff-only + $ git merge topic-b + $ git merge topic-c +------------ + +The procedure will result in a history that looks like this: + +------------ + C0--C1--------------C2 + / \ + ---o---o---A---X---Y---Z---W---M'--N' + \ / + B0--B1---------B2 +------------ + +See also http://git-blame.blogspot.com/2013/09/fun-with-first-parent-history.html diff --git a/Documentation/howto/maintain-git.txt b/Documentation/howto/maintain-git.txt index 33ae69c11f..ca4378740c 100644 --- a/Documentation/howto/maintain-git.txt +++ b/Documentation/howto/maintain-git.txt @@ -39,26 +39,26 @@ The policy on Integration is informally mentioned in "A Note from the maintainer" message, which is periodically posted to this mailing list after each feature release is made. - - Feature releases are numbered as vX.Y.Z and are meant to + - Feature releases are numbered as vX.Y.0 and are meant to contain bugfixes and enhancements in any area, including functionality, performance and usability, without regression. - One release cycle for a feature release is expected to last for eight to ten weeks. - - Maintenance releases are numbered as vX.Y.Z.W and are meant - to contain only bugfixes for the corresponding vX.Y.Z feature - release and earlier maintenance releases vX.Y.Z.V (V < W). + - Maintenance releases are numbered as vX.Y.Z and are meant + to contain only bugfixes for the corresponding vX.Y.0 feature + release and earlier maintenance releases vX.Y.W (W < Z). - 'master' branch is used to prepare for the next feature release. In other words, at some point, the tip of 'master' - branch is tagged with vX.Y.Z. + branch is tagged with vX.Y.0. - 'maint' branch is used to prepare for the next maintenance - release. After the feature release vX.Y.Z is made, the tip + release. After the feature release vX.Y.0 is made, the tip of 'maint' branch is set to that release, and bugfixes will accumulate on the branch, and at some point, the tip of the - branch is tagged with vX.Y.Z.1, vX.Y.Z.2, and so on. + branch is tagged with vX.Y.1, vX.Y.2, and so on. - 'next' branch is used to publish changes (both enhancements and fixes) that (1) have worthwhile goal, (2) are in a fairly @@ -86,6 +86,10 @@ this mailing list after each feature release is made. users are encouraged to test it so that regressions and bugs are found before new topics are merged to 'master'. +Note that before v1.9.0 release, the version numbers used to be +structured slightly differently. vX.Y.Z were feature releases while +vX.Y.Z.W were maintenance releases for vX.Y.Z. + A Typical Git Day ----------------- diff --git a/Documentation/howto/new-command.txt b/Documentation/howto/new-command.txt index d7de5a3e9e..15a4c8031f 100644 --- a/Documentation/howto/new-command.txt +++ b/Documentation/howto/new-command.txt @@ -94,8 +94,10 @@ your language, document it in the INSTALL file. 6. There is a file command-list.txt in the distribution main directory that categorizes commands by type, so they can be listed in appropriate subsections in the documentation's summary command list. Add an entry -for yours. To understand the categories, look at git-commands.txt -in the main directory. +for yours. To understand the categories, look at command-list.txt +in the main directory. If the new command is part of the typical Git +workflow and you believe it common enough to be mentioned in 'git help', +map this command to a common group in the column [common]. 7. Give the maintainer one paragraph to include in the RelNotes file to describe the new feature; a good place to do so is in the cover diff --git a/Documentation/howto/rebase-from-internal-branch.txt b/Documentation/howto/rebase-from-internal-branch.txt index 19ab604f1f..02cb5f758d 100644 --- a/Documentation/howto/rebase-from-internal-branch.txt +++ b/Documentation/howto/rebase-from-internal-branch.txt @@ -139,7 +139,7 @@ You fetch from upstream, but not merge. $ git fetch upstream This leaves the updated upstream head in .git/FETCH_HEAD but -does not touch your .git/HEAD nor .git/refs/heads/master. +does not touch your .git/HEAD or .git/refs/heads/master. You run "git rebase" now. $ git rebase FETCH_HEAD master diff --git a/Documentation/howto/recover-corrupted-object-harder.txt b/Documentation/howto/recover-corrupted-object-harder.txt index 6f33dac0e0..9c4cd0915f 100644 --- a/Documentation/howto/recover-corrupted-object-harder.txt +++ b/Documentation/howto/recover-corrupted-object-harder.txt @@ -38,7 +38,7 @@ zlib were failing). Reading the zlib source code, I found that "incorrect data check" means that the adler-32 checksum at the end of the zlib data did not match the inflated data. So stepping the data through zlib would not help, as it -did not fail until the very end, when we realize the crc does not match. +did not fail until the very end, when we realize the CRC does not match. The problematic bytes could be anywhere in the object data. The first thing I did was pull the broken data out of the packfile. I @@ -195,7 +195,7 @@ halfway through: ------- I let it run to completion, and got a few more hits at the end (where it -was munging the crc to match our broken data). So there was a good +was munging the CRC to match our broken data). So there was a good chance this middle hit was the source of the problem. I confirmed by tweaking the byte in a hex editor, zlib inflating the @@ -240,3 +240,240 @@ But more importantly, git's hashing and checksumming noticed a problem that easily could have gone undetected in another system. The result still compiled, but would have caused an interesting bug (that would have been blamed on some random commit). + + +The adventure continues... +-------------------------- + +I ended up doing this again! Same entity, new hardware. The assumption +at this point is that the old disk corrupted the packfile, and then the +corruption was migrated to the new hardware (because it was done by +rsync or similar, and no fsck was done at the time of migration). + +This time, the affected blob was over 20 megabytes, which was far too +large to do a brute-force on. I followed the instructions above to +create the `zlib` file. I then used the `inflate` program below to pull +the corrupted data from that. Examining that output gave me a hint about +where in the file the corruption was. But now I was working with the +file itself, not the zlib contents. So knowing the sha1 of the object +and the approximate area of the corruption, I used the `sha1-munge` +program below to brute-force the correct byte. + +Here's the inflate program (it's essentially `gunzip` but without the +`.gz` header processing): + +-------------------------- +#include <stdio.h> +#include <string.h> +#include <zlib.h> +#include <stdlib.h> + +int main(int argc, char **argv) +{ + /* + * oversized so we can read the whole buffer in; + * this could actually be switched to streaming + * to avoid any memory limitations + */ + static unsigned char buf[25 * 1024 * 1024]; + static unsigned char out[25 * 1024 * 1024]; + int len; + z_stream z; + int ret; + + len = read(0, buf, sizeof(buf)); + memset(&z, 0, sizeof(z)); + inflateInit(&z); + + z.next_in = buf; + z.avail_in = len; + z.next_out = out; + z.avail_out = sizeof(out); + + ret = inflate(&z, 0); + if (ret != Z_OK && ret != Z_STREAM_END) + fprintf(stderr, "initial inflate failed (%d)\n", ret); + + fprintf(stderr, "outputting %lu bytes", z.total_out); + fwrite(out, 1, z.total_out, stdout); + return 0; +} +-------------------------- + +And here is the `sha1-munge` program: + +-------------------------- +#include <stdio.h> +#include <unistd.h> +#include <string.h> +#include <signal.h> +#include <openssl/sha.h> +#include <stdlib.h> + +/* eye candy */ +static int counter = 0; +static void progress(int sig) +{ + fprintf(stderr, "\r%d", counter); + alarm(1); +} + +static const signed char hexval_table[256] = { + -1, -1, -1, -1, -1, -1, -1, -1, /* 00-07 */ + -1, -1, -1, -1, -1, -1, -1, -1, /* 08-0f */ + -1, -1, -1, -1, -1, -1, -1, -1, /* 10-17 */ + -1, -1, -1, -1, -1, -1, -1, -1, /* 18-1f */ + -1, -1, -1, -1, -1, -1, -1, -1, /* 20-27 */ + -1, -1, -1, -1, -1, -1, -1, -1, /* 28-2f */ + 0, 1, 2, 3, 4, 5, 6, 7, /* 30-37 */ + 8, 9, -1, -1, -1, -1, -1, -1, /* 38-3f */ + -1, 10, 11, 12, 13, 14, 15, -1, /* 40-47 */ + -1, -1, -1, -1, -1, -1, -1, -1, /* 48-4f */ + -1, -1, -1, -1, -1, -1, -1, -1, /* 50-57 */ + -1, -1, -1, -1, -1, -1, -1, -1, /* 58-5f */ + -1, 10, 11, 12, 13, 14, 15, -1, /* 60-67 */ + -1, -1, -1, -1, -1, -1, -1, -1, /* 68-67 */ + -1, -1, -1, -1, -1, -1, -1, -1, /* 70-77 */ + -1, -1, -1, -1, -1, -1, -1, -1, /* 78-7f */ + -1, -1, -1, -1, -1, -1, -1, -1, /* 80-87 */ + -1, -1, -1, -1, -1, -1, -1, -1, /* 88-8f */ + -1, -1, -1, -1, -1, -1, -1, -1, /* 90-97 */ + -1, -1, -1, -1, -1, -1, -1, -1, /* 98-9f */ + -1, -1, -1, -1, -1, -1, -1, -1, /* a0-a7 */ + -1, -1, -1, -1, -1, -1, -1, -1, /* a8-af */ + -1, -1, -1, -1, -1, -1, -1, -1, /* b0-b7 */ + -1, -1, -1, -1, -1, -1, -1, -1, /* b8-bf */ + -1, -1, -1, -1, -1, -1, -1, -1, /* c0-c7 */ + -1, -1, -1, -1, -1, -1, -1, -1, /* c8-cf */ + -1, -1, -1, -1, -1, -1, -1, -1, /* d0-d7 */ + -1, -1, -1, -1, -1, -1, -1, -1, /* d8-df */ + -1, -1, -1, -1, -1, -1, -1, -1, /* e0-e7 */ + -1, -1, -1, -1, -1, -1, -1, -1, /* e8-ef */ + -1, -1, -1, -1, -1, -1, -1, -1, /* f0-f7 */ + -1, -1, -1, -1, -1, -1, -1, -1, /* f8-ff */ +}; + +static inline unsigned int hexval(unsigned char c) +{ +return hexval_table[c]; +} + +static int get_sha1_hex(const char *hex, unsigned char *sha1) +{ + int i; + for (i = 0; i < 20; i++) { + unsigned int val; + /* + * hex[1]=='\0' is caught when val is checked below, + * but if hex[0] is NUL we have to avoid reading + * past the end of the string: + */ + if (!hex[0]) + return -1; + val = (hexval(hex[0]) << 4) | hexval(hex[1]); + if (val & ~0xff) + return -1; + *sha1++ = val; + hex += 2; + } + return 0; +} + +int main(int argc, char **argv) +{ + /* oversized so we can read the whole buffer in */ + static unsigned char buf[25 * 1024 * 1024]; + char header[32]; + int header_len; + unsigned char have[20], want[20]; + int start, len; + SHA_CTX orig; + unsigned i, j; + + if (!argv[1] || get_sha1_hex(argv[1], want)) { + fprintf(stderr, "usage: sha1-munge <sha1> [start] <file.in\n"); + return 1; + } + + if (argv[2]) + start = atoi(argv[2]); + else + start = 0; + + len = read(0, buf, sizeof(buf)); + header_len = sprintf(header, "blob %d", len) + 1; + fprintf(stderr, "using header: %s\n", header); + + /* + * We keep a running sha1 so that if you are munging + * near the end of the file, we do not have to re-sha1 + * the unchanged earlier bytes + */ + SHA1_Init(&orig); + SHA1_Update(&orig, header, header_len); + if (start) + SHA1_Update(&orig, buf, start); + + signal(SIGALRM, progress); + alarm(1); + + for (i = start; i < len; i++) { + unsigned char c; + SHA_CTX x; + +#if 0 + /* + * deletion -- this would not actually work in practice, + * I think, because we've already committed to a + * particular size in the header. Ditto for addition + * below. In those cases, you'd have to do the whole + * sha1 from scratch, or possibly keep three running + * "orig" sha1 computations going. + */ + memcpy(&x, &orig, sizeof(x)); + SHA1_Update(&x, buf + i + 1, len - i - 1); + SHA1_Final(have, &x); + if (!memcmp(have, want, 20)) + printf("i=%d, deletion\n", i); +#endif + + /* + * replacement -- note that this tries each of the 256 + * possible bytes. If you suspect a single-bit flip, + * it would be much shorter to just try the 8 + * bit-flipped variants. + */ + c = buf[i]; + for (j = 0; j <= 0xff; j++) { + buf[i] = j; + + memcpy(&x, &orig, sizeof(x)); + SHA1_Update(&x, buf + i, len - i); + SHA1_Final(have, &x); + if (!memcmp(have, want, 20)) + printf("i=%d, j=%02x\n", i, j); + } + buf[i] = c; + +#if 0 + /* addition */ + for (j = 0; j <= 0xff; j++) { + unsigned char extra = j; + memcpy(&x, &orig, sizeof(x)); + SHA1_Update(&x, &extra, 1); + SHA1_Update(&x, buf + i, len - i); + SHA1_Final(have, &x); + if (!memcmp(have, want, 20)) + printf("i=%d, addition=%02x", i, j); + } +#endif + + SHA1_Update(&orig, buf + i, 1); + counter++; + } + + alarm(0); + fprintf(stderr, "\r%d\n", counter); + return 0; +} +-------------------------- diff --git a/Documentation/howto/revert-a-faulty-merge.txt b/Documentation/howto/revert-a-faulty-merge.txt index acf3e477e5..19f59cc888 100644 --- a/Documentation/howto/revert-a-faulty-merge.txt +++ b/Documentation/howto/revert-a-faulty-merge.txt @@ -30,7 +30,7 @@ The history immediately after the "revert of the merge" would look like this: ---o---o---o---M---x---x---W - / + / ---A---B where A and B are on the side development that was not so good, M is the @@ -47,14 +47,14 @@ After the developers of the side branch fix their mistakes, the history may look like this: ---o---o---o---M---x---x---W---x - / + / ---A---B-------------------C---D where C and D are to fix what was broken in A and B, and you may already have some other changes on the mainline after W. If you merge the updated side branch (with D at its tip), none of the -changes made in A nor B will be in the result, because they were reverted +changes made in A or B will be in the result, because they were reverted by W. That is what Alan saw. Linus explains the situation: @@ -81,7 +81,7 @@ In such a situation, you would want to first revert the previous revert, which would make the history look like this: ---o---o---o---M---x---x---W---x---Y - / + / ---A---B-------------------C---D where Y is the revert of W. Such a "revert of the revert" can be done @@ -90,17 +90,17 @@ with: $ git revert W This history would (ignoring possible conflicts between what W and W..Y -changed) be equivalent to not having W nor Y at all in the history: +changed) be equivalent to not having W or Y at all in the history: ---o---o---o---M---x---x-------x---- - / + / ---A---B-------------------C---D and merging the side branch again will not have conflict arising from an earlier revert and revert of the revert. ---o---o---o---M---x---x-------x-------* - / / + / / ---A---B-------------------C---D Of course the changes made in C and D still can conflict with what was @@ -111,13 +111,13 @@ faulty A and B, and redone the changes on top of the updated mainline after the revert, the history would have looked like this: ---o---o---o---M---x---x---W---x---x - / \ + / \ ---A---B A'--B'--C' If you reverted the revert in such a case as in the previous example: ---o---o---o---M---x---x---W---x---x---Y---* - / \ / + / \ / ---A---B A'--B'--C' where Y is the revert of W, A' and B' are rerolled A and B, and there may @@ -129,7 +129,7 @@ lot of overlapping changes that result in conflicts. So do not do "revert of revert" blindly without thinking.. ---o---o---o---M---x---x---W---x---x - / \ + / \ ---A---B A'--B'--C' In the history with rebased side branch, W (and M) are behind the merge diff --git a/Documentation/howto/revert-branch-rebase.txt b/Documentation/howto/revert-branch-rebase.txt index 85f69dbac9..149508e13b 100644 --- a/Documentation/howto/revert-branch-rebase.txt +++ b/Documentation/howto/revert-branch-rebase.txt @@ -137,7 +137,7 @@ $ make clean test ;# make sure it did not cause other breakage. ------------------------------------------------ Everything is in the good order. I do not need the temporary branch -nor tag anymore, so remove them: +or tag anymore, so remove them: ------------------------------------------------ $ rm -f .git/refs/tags/pu-anchor diff --git a/Documentation/howto/setup-git-server-over-http.txt b/Documentation/howto/setup-git-server-over-http.txt index 6de4f3c487..f44e5e9458 100644 --- a/Documentation/howto/setup-git-server-over-http.txt +++ b/Documentation/howto/setup-git-server-over-http.txt @@ -181,7 +181,7 @@ On Debian: Most tests should pass. -A command line tool to test WebDAV is cadaver. If you prefer GUIs, for +A command-line tool to test WebDAV is cadaver. If you prefer GUIs, for example, konqueror can open WebDAV URLs as "webdav://..." or "webdavs://...". |