679b79c5e5
Import modules between files using the syntax `from . import foobar`, renaming what used to be `FooBar` to `foobar.FooBar` when moved to a separate file. In __init__.py only import what is meant to be public API. Signed-off-by: Tom Gundersen <teg@jklm.no>
87 lines
3.1 KiB
Python
87 lines
3.1 KiB
Python
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import contextlib
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import errno
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import hashlib
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import os
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import subprocess
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import tempfile
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from . import treesum
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__all__ = [
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"ObjectStore",
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]
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class ObjectStore:
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def __init__(self, store):
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self.store = store
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self.objects = f"{store}/objects"
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self.refs = f"{store}/refs"
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os.makedirs(self.store, exist_ok=True)
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os.makedirs(self.objects, exist_ok=True)
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os.makedirs(self.refs, exist_ok=True)
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def has_tree(self, tree_id):
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if not tree_id:
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return False
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return os.access(f"{self.refs}/{tree_id}", os.F_OK)
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@contextlib.contextmanager
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def get_tree(self, tree_id):
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with tempfile.TemporaryDirectory(dir=self.store) as tmp:
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if tree_id:
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subprocess.run(["mount", "-o", "bind,ro,mode=0755", f"{self.refs}/{tree_id}", tmp], check=True)
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try:
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yield tmp
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finally:
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subprocess.run(["umount", "--lazy", tmp], check=True)
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else:
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# None was given as tree_id, just return an empty directory
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yield tmp
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@contextlib.contextmanager
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def new_tree(self, tree_id, base_id=None):
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with tempfile.TemporaryDirectory(dir=self.store) as tmp:
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# the tree that is yielded will be added to the content store
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# on success as tree_id
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tree = f"{tmp}/tree"
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link = f"{tmp}/link"
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os.mkdir(tree, mode=0o755)
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if base_id:
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# the base, the working tree and the output tree are all on
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# the same fs, so attempt a lightweight copy if the fs
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# supports it
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subprocess.run(["cp", "--reflink=auto", "-a", f"{self.refs}/{base_id}/.", tree], check=True)
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yield tree
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# if the yield raises an exception, the working tree is cleaned
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# up by tempfile, otherwise, we save it in the correct place:
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fd = os.open(tree, os.O_DIRECTORY)
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try:
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m = hashlib.sha256()
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treesum.treesum(m, fd)
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treesum_hash = m.hexdigest()
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finally:
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os.close(fd)
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# the tree is stored in the objects directory using its content
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# hash as its name, ideally a given tree_id (i.e., given config)
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# will always produce the same content hash, but that is not
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# guaranteed
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output_tree = f"{self.objects}/{treesum_hash}"
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try:
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os.rename(tree, output_tree)
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except OSError as e:
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if e.errno == errno.ENOTEMPTY:
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pass # tree with the same content hash already exist, use that
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else:
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raise
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# symlink the tree_id (config hash) in the refs directory to the treesum
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# (content hash) in the objects directory. If a symlink by that name
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# alreday exists, atomically replace it, but leave the backing object
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# in place (it may be in use).
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os.symlink(f"../objects/{treesum_hash}", link)
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os.replace(link, f"{self.refs}/{tree_id}")
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