In-tree crate built-in.rlib support? #1091

Hello, everyone. So recently i've been working on a possible rewrite of a filesystem module in rust. I'm already implemented a small and thin core-only crate (which is also used for userspace progs) and i want to embed it into kernel tree . Given the current status of vfs, the code only provides some ffi hooks to the original C implementations before the virtual filesystem abstraction is ready to be merged. But i have some problems here.

1. Apart from the default kernel/core/alloc cfg provided in rust/Makefile, can i specify my own extra cfgs for rustc so that my in-kernel rust driver source can find the crate i introduce?
2. Are there any built-in rlib recipes so that i can designate a lib.rs and produce a rlib file and then make it to the linking stage?
3. It seems that in the current implementation of generate_rust_analyzer.py, the code only provides only minimal deps configs for kernel/core/alloc crate and does not respect the KBuild/Makefile if i want to introduce some module-local crates that also depends on kernel crate there. I've looked through Third-party crates support: proc-macro2, quote, syn, serde and serde_derive #1007 which seems to introduce those crates kernel-wide, however i want to keep it module-local. So maybe we need some enhancements on this part too?

for folder in extra_dirs:
        for path in folder.rglob("*.rs"):
            logging.info("Checking %s", path)
            name = path.name.replace(".rs", "")

            # Skip those that are not crate roots.
            if not is_root_crate(path.parent / "Makefile", name) and \
               not is_root_crate(path.parent / "Kbuild", name):
                continue

            logging.info("Adding %s", name)
            append_crate(
                name,
                path,
                ["core", "alloc", "kernel"],
                cfg=cfg,
            )

Any help or replies are much appreciated! Thanks!