get rid of check_path(), it's overly complicated. Instead, inline open_file() in client_read() and rework open_dir() to just use openat() instead of the complicate dance it was doing. Simplify open_dir() too in the process: if the directory entry for the index is not a regular file, pretend it doesn't exist.

in those cases we need to reschedule the function and return, instead of going on with the cleanup.