Several FUSE ops fell back to looking up a FileInfo via
state.open_files when the kernel-provided fh was zero, returning
-ENOENT if the lookup failed. This path papered over handle-tracking
bugs and added cost on every call. Use the handle directly and
return -EBADF when it is invalid - the kernel should always hand us
a valid fh for an open resource.
Also simplify FileInfo::from_fh / DirInfo::from_fh and their to_fh
helpers: callers now handle the null-pointer case explicitly so the
ASSERT_NOT_NULL checks are redundant.
Covers fallocate, fchmod, fchown, fgetattr, flock, ftruncate,
futimens, read, release, releasedir, write, statx, ioctl (file +
dir), readdir (sequential, concurrent-on-read,
concurrent-on-search), and the passthrough fast paths in
create/open.
addresses #521
mergerfs is written using libfuse's high level API. The HLAPI forces a certain
behavior with regard to unlinking or rename overwriting of open files. It
renames the file to .fuse_hiddenXXXXXX and when incoming requests refer
to the unlinked file it will use path based calls and use that path.
This behavior leads to rmdirs failing or some software noticing
the .fuse_hidden files.
This patch changes the HLAPI and removes entirely the .fuse_hidden behavior.
See the README for more.
