In an effort to rewrite `bch2_read_super` from C to Rust,
it is neccessary to have `opt_get!` macro defined, and some
FMODE_* consts (defined as macro in `include/linux/blkdev.h`)
defined as Rust const.
Bindgen is currently unable to exapnd C functional macro [1],
this this commit use the workaround as introduced in [2].
[1] https://github.com/rust-lang/rust-bindgen/issues/753
[2] https://github.com/rust-lang/rust-bindgen/issues/753#issuecomment-608546390
Signed-off-by: TruongSinh Tran-Nguyen <i@truongsinh.pro>
This implements opt_set!(), which works exactly the same as the C
version and allows filesystem options to be specified in Rust code.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
