Support for filesystem abstractions

[ariel-miculas]

I've opened this issue to track the missing pieces for the initial rust filesystem abstractions.
I have backported @wedsonaf's branch fs on top of rust-next to get a sense about the missing modules, see rust-next-fs.
Here's a list of the missing parts:

• modules: cred, delay, file, fs, fs/param, io_buffer, iov_iter, mm, pages, user_ptr
• macros: count_paren_items in driver.rs, from_kernel_result in error.rs, offset_of/container_of in lib.rs
• allocator_api in rust_allowed_features
• unstable features: associated_type_defaults, c_size_t, const_mut_refs, duration_constants
• some helper functions in rust/helpers.c

The dependencies between the modules are:

• fs depends on file, delay and fs/param
• file depends on cred, fs, mm, io_buffer, iov_iter and user_ptr
• mm depends on pages
• iov_iter depends on io_buffer
• pages depends on io_buffer
• user_ptr depends on io_buffer

One strategy would be to start bottom-up, starting with io_buffer, page, iov_iter, cred and user_ptr and then continue with the rest. Remains to be seen how much of the code can be backported as it is and how much it needs to be changed.

[jyizheng]

I am happy to contribute to this issue.

[ariel-miculas]

The latest development is this patch series by Wedson Almeida which introduces abstractions for read-only filesystems.

[ariel-miculas]

FYI Wedson recently sent another patch series for the filesystem abstractions: https://lore.kernel.org/rust-for-linux/20240514131711.379322-1-wedsonaf@gmail.com/