1Def.: Shallow commits do have parents, but not in the shallow 2repo, and therefore grafts are introduced pretending that 3these commits have no parents. 4 5The basic idea is to write the SHA1s of shallow commits into 6$GIT_DIR/shallow, and handle its contents like the contents 7of $GIT_DIR/info/grafts (with the difference that shallow 8cannot contain parent information). 9 10This information is stored in a new file instead of grafts, or 11even the config, since the user should not touch that file 12at all (even throughout development of the shallow clone, it 13was never manually edited!). 14 15Each line contains exactly one SHA1. When read, a commit_graft 16will be constructed, which has nr_parent < 0 to make it easier 17to discern from user provided grafts. 18 19Since fsck-objects relies on the library to read the objects, 20it honours shallow commits automatically. 21 22There are some unfinished ends of the whole shallow business: 23 24- maybe we have to force non-thin packs when fetching into a 25 shallow repo (ATM they are forced non-thin). 26 27- A special handling of a shallow upstream is needed. At some 28 stage, upload-pack has to check if it sends a shallow commit, 29 and it should send that information early (or fail, if the 30 client does not support shallow repositories). There is no 31 support at all for this in this patch series. 32 33- Instead of locking $GIT_DIR/shallow at the start, just 34 the timestamp of it is noted, and when it comes to writing it, 35 a check is performed if the mtime is still the same, dying if 36 it is not. 37 38- It is unclear how "push into/from a shallow repo" should behave. 39 40- If you deepen a history, you'd want to get the tags of the 41 newly stored (but older!) commits. This does not work right now. 42 43To make a shallow clone, you can call "git-clone --depth 20 repo". 44The result contains only commit chains with a length of at most 20. 45It also writes an appropriate $GIT_DIR/shallow. 46 47You can deepen a shallow repository with "git-fetch --depth 20 48repo branch", which will fetch branch from repo, but stop at depth 4920, updating $GIT_DIR/shallow.