Optional reachability checks for direct object access
konstantin at linuxfoundation.org
Tue Oct 27 21:43:23 CET 2020
It is common for git hosting environments to configure all forks of the
same repo to use an "object storage" repository. For example, this is
what allows git.kernel.org's 600+ forks of linux.git to take up only
10GB on disk as opposed to 800GB.
One of the side-effects of this setup is that any object in the shared
repository can be accessed from any of the forks, which periodically
confuses people into believing that something terrible has happened.
Case in point:
Now, this could be fixed by performing reachability checks, but they are
expensive, so it makes sense to have this off in most cases. However, I
think it would be a nice feature to be able to enable this
per-repository -- for example, to avoid someone getting confused when
they see odd objects in what would appear to be the official Linux
Git-upload-pack implements this, which is why it's possible to set
The easiest way to check if an object is reachable from a repository
that I can think of is to run "git branch --contains [commit-id]" and
checking if anything is returned. E.g., a commit
184c79e4acf5a55f1d6febcf4cf1b545880c2fde doesn't exist in
torvalds/linux.git, but git finds it just fine through alternates:
$ git cat-file -t 184c79e4acf5a55f1d6febcf4cf1b545880c2fde
And you can access it via cgit:
However, it doesn't exist in that tree:
$ git branch --contains 184c79e4acf5a55f1d6febcf4cf1b545880c2fde
If cgit could optionally perform this (or similar) check and return 404
if a repo is configured to only display reachable objects, that would
help avoid confusion. Afaict, it's not even that expensive when
commit-graphs are regularly built. For example, the above check only
takes 0m0.034s of sys time, according to "time".
What do you think?
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