[PATCH] D97850: Fix PCM read from ModuleCache for ext4 filesystem

[Duncan P. N. Exon Smith via Phabricator via cfe-commits]

dexonsmith added a comment.

In D97850#2629464 <https://reviews.llvm.org/D97850#2629464>, @ilyakuteev wrote:

> If a fix will be in ModuleManager and only for ModuleCache the problem with symlinks and path will not affect it as ModuleCache is managed by clang and we can rely on it.
> I agree that using `FileMgr.getBypassFile` is not the best way to solve this problem, we need to replace `FileMgr.getFileRef` with some other method but I did not found such method in FileManager. Maybe we need to add one or not use FileManager as was mentioned. Not sure which way is better and safer.

FileManager plays two roles (unless I'm missing a third?):

- Establish an identity for multiple paths that should be treated as "the same" (address of FileEntry).
- Cache stat information (the content of FileEntry).

This patch is predicated on it being safe to skip the former (makes sense to me, although I think clang is a bit inconsistent about using relative paths for the module cache, so there might be some work to do). We already skip / avoid the latter (ModuleManager is the only caller of FileManager::getNoncachedStatValue). Seems like skipping the FileManager will simplify both the ModuleManager and the FileManager.

Might be worth an RFC on cfe-dev?


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