Someone at $DAYJOB noticed that if a .gitmodules-containing tree and the .gitmodules blob itself are sent in 2 separate packfiles during a fetch (which can happen when packfile URIs are used), transfer.fsckobjects causes the fetch to fail. You can reproduce it as follows (as of the time of writing): $ git -c fetch.uriprotocols=https -c transfer.fsckobjects=true clone https://chromium.googlesource.com/chromiumos/codesearch Cloning into 'codesearch'... remote: Total 2242 (delta 0), reused 2242 (delta 0) Receiving objects: 100% (2242/2242), 1.77 MiB | 4.62 MiB/s, done. error: object 1f155c20935ee1154a813a814f03ef2b3976680f: gitmodulesMissing: unable to read .gitmodules blob fatal: fsck error in pack objects fatal: index-pack failed This happens because the fsck part is currently being done in index-pack, which operates on one pack at a time. When index-pack sees the tree, it runs fsck on it (like any other object), and the fsck subsystem remembers the .gitmodules target (specifically, in gitmodules_found in fsck.c). Later, index-pack runs fsck_finish() which checks if the target exists, but it doesn't, so it reports the failure. One option is for fetch to do its own pass of checking all downloaded objects once all packfiles have been downloaded, but that seems wasteful as all trees would have to be re-inflated. Another option is to do it within the connectivity check instead - so, update rev-list and the object walking mechanism to be able to detect .gitmodules in trees and fsck the target blob whenever such an entry occurs. This has the advantage that there is no extra re-inflation, although it might be strange to have object walking be able to fsck. The simplest solution would be to just relax this - check the blob if it exists, but if it doesn't, it's OK. Some things in favor of this solution: - This is something we already do in the partial clone case (although it could be argued that in this case, we're already trusting the server for far more than .gitmodules, so just because it's OK in the partial clone case doesn't mean that it's OK in the regular case). - Also, the commit message for this feature (from ed8b10f631 ("fsck: check .gitmodules content", 2018-05-21)) gives a rationale of a newer server being able to protect older clients. - Servers using receive-pack (instead of fetch-pack) to obtain objects would still be protected, since receive-pack still only accepts one packfile at a time (and there are currently no plans to expand this). - Also, malicious .gitobjects files could still be crafted that pass fsck checking - for example, by containing a URL (of another server) that refers to a repo with a .gitobjects that would fail fsck. So I would rather go with just relaxing the check, but if consensus is that we should still do it, I'll investigate doing it in the connectivity check.
