fix conflicting push situation
In a situation where there are two repos that are diverged and each pushes in turn to git-remote-annex, the first to push updates it. Then the second push fails because it is not a fast-forward. The problem is, before git push fails with "non-fast-forward", it actually calls git-remote-annex with push. So, to the user it appears as if the push failed, but it actually reached the remote, and overwrote the other push! The only solution to this seems to be for git-remote-annex push to notice when a non-force-push would overwrite a ref stored in the remote, and refuse to push that ref, returning an error to git. This seems strange, why would git make remote helpers implement that when it later checks the same thing itself? With this fix, it's still possible for a race to overwrite a change to the MANIFEST and lose work that was pushed from the other repo. But that needs two pushes to be running at the same time. From the user's perspective, that situation is the same as if one repo pushed new work, then the other repo did a git push --force, overwriting the first repo's push. In the first repo, another push will then fail as a non fast-forward, and the user can recover as usual. But, a MANIFEST overwrite will leave bundle files in the remote that are not listed in the MANIFEST. It seems likely that git-annex will eventually be able to detect that after the fact and clean it up. Eg, it can learn all bundles that are stored in the remote using the location log, and compare them to the MANIFEST to find bundles that got lost. The race can also appear to the user as if they pushed a ref, but then it got deleted from the remote. This happens when two two pushes are pushing different ref names. This might be harder for the user to notice; git fetch does not indicate that a remote ref got deleted. They would have to use git fetch --prune to notice the deletion. Once the user does notice, they can re-push their ref to recover. Sponsored-by: Jack Hill on Patreon
This commit is contained in:
Joey Hess
parent
99491f572f
commit
8b56d6b283
2 changed files with 107 additions and 66 deletions
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@ -35,11 +35,9 @@ objects, but not refs.
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objects
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2. hash to calculate GITBUNDLE object name
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3. upload GITBUNDLE object
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4. download current manifest
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5. remove all old GITBUNDLES from the manifest, and add new GITBUNDLE at
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the end. Note that it's possible for the manifest to contain GITBUNDLES
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that were not in the last fetched manifest, if so those must be
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preserved, and the new GITBUNDLE appended
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4. download old manifest
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4. upload new manifest listing only the single new GITBUNDLE
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5. delete all other GITBUNDLEs that were listed in the old manifest
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# multiple GITMANIFEST files
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@ -7,6 +7,8 @@ set -x
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# remember the refs that were uploaded already
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git for-each-ref refs/namespaces/mine/ > .git/old-refs
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rm -f .git/push-response
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# Unfortunately, git bundle omits prerequisites that are omitted once,
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# even if they are used by a later ref.
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# For example, where x is a ref that points at A, and y is a ref
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@ -42,10 +44,13 @@ while read foo; do
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# includes all refs in its bundle.
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f=$(tail -n 1 $TOPDIR/MANIFEST)
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if [ -n "$f" ]; then
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# stash the listed refs for later
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# checking in push
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git bundle list-heads $TOPDIR/$f > .git/listed-refs
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# refs in the bundle may end up prefixed with refs/namespaces/mine/
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# when the intent is for the bundle to include a
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# ref with the name that comes after that.
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git bundle list-heads $TOPDIR/$f | sed 's/refs\/namespaces\/mine\///'
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sed 's/refs\/namespaces\/mine\///' .git/listed-refs
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fi
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fi
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echo
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@ -56,12 +61,13 @@ while read foo; do
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push*)
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set -- $foo
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x="$2"
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# src ref if prefixed with a + in a forced push
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# src ref is prefixed with a + in a forced push
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forcedpush=""
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if echo "$x" | cut -d : -f 1 | egrep -q '^\+'; then
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forcedpush=1
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fi
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srcref="$(echo "$x" | cut -d : -f 1 | sed 's/^\+//')"
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dstref="$(echo "$x" | cut -d : -f 2)"
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if [ -z "$srcref" ]; then
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git update-ref -d refs/namespaces/mine/"$dstref"
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else
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# Need to create a bundle containing $dstref, but
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# don't want to overwrite that ref in the local
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# repo. Unfortunately, git bundle does not support
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@ -70,7 +76,31 @@ while read foo; do
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# Instead, just create a ref under the namespace
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# refs/namespaces/mine/ that will be put in the
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# bundle.
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git update-ref refs/namespaces/mine/"$dstref" "$srcref"
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mydstref=refs/namespaces/mine/"$dstref"
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if [ -z "$srcref" ]; then
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git update-ref -d "$mydstref"
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touch .git/push-response
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echo "ok $dstref" >> .git/push-response
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else
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if [ ! "$forcedpush" ]; then
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# check if the push would overwrite
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# work in the ref currently stored in the
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# remote, if so refuse to do it
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prevsha=$(grep " $mydstref$" .git/listed-refs | awk '{print $1}')
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newsha=$(git rev-parse "$srcref")
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if [ -n "$prevsha" ] && [ "$prevsha" != "$newsha" ] && [ -z "$(git log --oneline $prevsha..$newsha 2>/dev/null)" ]; then
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touch .git/push-response
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echo "error $dstref non-fast-forward" >> .git/push-response
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else
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touch .git/push-response
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echo "ok $dstref" >> .git/push-response
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git update-ref "$mydstref" "$srcref"
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fi
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else
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git update-ref "$mydstref" "$srcref"
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touch .git/push-response
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echo "ok $dstref" >> .git/push-response
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fi
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fi
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dopush=1
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;;
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@ -89,6 +119,16 @@ while read foo; do
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dofetch=""
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fi
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if [ "$dopush" ]; then
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# if some refs cannot be pushed, refuse to
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# push anything. It would be difficult to
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# push only some refs, because the bundle
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# needs to contain all refs, and some refs
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# on the remote may contain objects we have
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# not fetched yet.
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if egrep -q "^error" .git/push-response; then
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sed 's/^ok \(.*\)/error \1 unable to push this due to other pushed ref being non-fast-forward/' .git/push-response > .git/push-response.new
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mv .git/push-response.new .git/push-response
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else
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if [ -z "$(git for-each-ref refs/namespaces/mine/)" ]; then
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# deleted all refs
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if [ -e "$TOPDIR/MANIFEST" ]; then
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@ -146,6 +186,9 @@ while read foo; do
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mv $TOPDIR/new.bundle "$TOPDIR/$sha1.bundle"
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echo "$sha1.bundle" >> $TOPDIR/MANIFEST
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fi
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fi
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cat .git/push-response
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rm -f .git/push-response
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echo
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dopush=""
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fi
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