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49 lines
2.1 KiB
Plaintext
49 lines
2.1 KiB
Plaintext
Some libraries that Ceph uses are incorporated into the build tree
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through a technique known as git subtrees. This is an alternative to
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git submodules, which is also used in Ceph.
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One such library is the dmclock library. Here are some basic notes on
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the use of git subtrees.
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When a subtree is added to the repo, commands such as these were run
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from the top-level ceph directory:
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git subtree add --prefix src/dmclock \
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git@github.com:ceph/dmclock.git master --squash
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That essentially brings in a full copy of the library into the
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subdirectory src/dmclock, but squashes all the commits into a single
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one.
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If in time the library is updated and you'd like to bring the updates
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in, you could run:
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git subtree pull --prefix src/dmclock \
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git@github.com:ceph/dmclock.git master --squash
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WARNINGS
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1. A rebase should NEVER include the commits by which a subtree is
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added or pulled. Those commits do not include the prefix that was used
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for the subtree add/pull, and therefore the commits are applied to the
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wrong files or, more likely, to non-existant files. If something like
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this must be done, a workable approach is to a) do an interactive
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rebase, b) remove the commits for the former subtree add/pull, and
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either c) replace those commits with executions (x/exec) of the
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commands used to add/pull the subtrees, or d) do those commands from
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the command-line by using (e/edit) on preceding commits.
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2. If you'd like to modify the library contained in a subtree you'll
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need to choose whether to just change your subtree and maintain those
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differences into the future (until the library incorporates them) or,
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if you're able, modify the library and use a "git subtree pull ..." to
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bring them in.
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3. If you modify the library within the ceph tree, then it's best not
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to combine changes within the subtree and outside the subtree in a
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single commit. Each commit should either only contain changes within
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the subtree or outside the subtree. That gives you the option to
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cleanly push those changes back to the library's repo. That way if you
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ultimately decide to make the changes to the library, you can easily
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remove the subtree commits.
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