* perf: answer Steam's missing-file checks on FUSE libraries from the directory cache
Before creating and committing each file, the Steam client checks whether it
already exists under its exact, lower-cased and folded spellings. On an SD or
USB library reached through Android's FUSE layer every one of those misses is a
round trip to MediaProvider (Brawlhalla: about 65,000 misses, 92 of the 161 s
of preallocation and 60 of the 93 s of commit).
The client already caches the listings of its steamapps directories on FUSE and
keeps them exact through its own changes, inotify and a short TTL. access() now
answers a name that is absent from a live listing of its directory without
asking the filesystem. Directory paths match case-insensitively only when the
library's filesystem folds case, and names compare case-insensitively, so an
existing file is never reported missing.
* fix: reuse a listing for a differently cased folder only when the whole path folds case
Checking that steamapps alone folds case let a listing of one folder answer
for a different folder below it whose name differs only in case. The fill
now compares the listed folder with its fully case-swapped path below
steamapps, so a listing is reused across case only when the filesystem
folds every level.
* fix(dircache): match a folded listing only below the same prefix and skip it during a tracked change
* fix(linuxfs): a folder renamed or removed above a cached listing drops that listing
* fix(linuxfs): watch the folders above a cached listing so a rename or removal by any process drops it
* fix(linuxfs): also watch the folders above steamapps, and stop a stuck probe from hanging the tests
* fix(linuxfs): a listing under a symlink or an unwatchable folder no longer answers absent lookups
* fix(linuxfs): a symlink check that cannot be watched also stops absent answers
* fix(linuxfs): a differently cased lookup reuses a listing only for the same folder
* fix: keep Steam's directory listings on FUSE libraries
Before it creates, moves or deletes a content file the Steam client lists
the whole destination directory about ten times to match names
case-insensitively. On Android's FUSE storage every listing goes through
the media provider, so reserving space grew quadratically with the number
of files: 33 minutes for Haunted Paws Demo (3,938 files) in a Games folder.
The client's listings under steamapps/ on FUSE are now kept while the
directory's stat is unchanged, for at most five seconds, and patched by
the client's own creates, renames and removals. Other changes fail the
stat check and the directory is read again. BL_NO_DIR_CACHE=1 turns it off.
Haunted Paws Demo into the internal shared Games folder: reserving space
33m08s -> 25-52s, committing 6m15s -> 19-30s, install 39m50s -> 1m12s-1m51s.
Internal storage is unchanged (5s reserve).
* fix: drop stale directory listings on coarse-timestamp volumes
NTFS reports whole-second directory times and a fixed size, so a change
made outside the client's own calls could leave a cached listing stale.
Listings now carry an inotify watch and are dropped on any event the
client's own patched changes don't account for. A forked child stops
caching, since it shares the parent's queue.
Covers rewinddir, telldir and seekdir on cached listings, and directories
opened by the fast-path preload's opendir, which goes through fdopendir.
MaxsTechReview