Separate file events and dir events

[krs85]

Example use: When skipping a program, say the program creates a dir and puts a bunch of files in there. If we try to copy outputs to a dir that doesn't exist yet, it will error. It is much simpler to just take care of the dir postconditions first (in apply_all_transitions()), and it's fairly simple to separate them within the ExecFileEvents struct.

Potential dir actions (SyscallEvents) that need to be handled separately from files:

• statfs
• create
• delete (rmdir, unlinkat(flags = AT_REMOVEDIR)
• rename: future TODO
• getdents

Other:

• Separate the file SyscallEvents from dir ones
• ExecFileEvents -> ExecSyscallEvents(FileEvents, DirEvents)
• generate_file_preconditions()
• generate_file_postconditions()
• generate_dir_preconditions()
• generate_dir_postconditions()
• generate_postconditions() -> calls both
• generate_preconditions() -> calls both
• update_based_on_syscall() -> LastMod. update based on file event, update based on dir event.
• update_based_on_syscalls() -> FirstState. update based on file event, update based on dir event.
• copying to the cache (generate_list_of_files_to_copy_to_cache). Don't have to do anything here with dirs.
• serving from the cache (apply_transition_function). Need to do: create, rename, delete. Separate function for dirs.
• stdout files (copied to cache + removed from starting cwd)