The minimizing filesystem used by the dependency scanner isn't great when it comes to the consistency of its caches. There are two problems that can be exposed by a filesystem that changes during dependency scan:
- In-memory cache entries for original and minimized files are distinct, populated at different times using separate stat/open syscalls. This means that when a file is read with minimization disabled, its contents might be inconsistent when the same file is read with minimization enabled at later point (and vice versa).
- In-memory cache entries are indexed by filename. This is problematic for symlinks, where the contents of the symlink might be inconsistent with contents of the original file (for the same reason as in problem 1).
This patch ensures consistency by always stating/reading a file exactly once. The original contents are always cached and minimized contents are derived from that on demand. The cache entries are now indexed by their UniqueID ensuring consistency for symlinks too. Moreover, the stat/read syscalls are now issued outside of critical section.
Depends on D115935.
This should mention that it's shared across different filenames, only one per UID now, and the filename is empty in the stat.