chore(rust): add opt_get! and expose some FMODE_* as Rust const

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>

1 files changed, 28 insertions, 2 deletions

diff --git a/rust-src/bch_bindgen/src/opts.rs b/rust-src/bch_bindgen/src/opts.rs
index e2261993..d38d469c 100644
--- a/rust-src/bch_bindgen/src/opts.rs
+++ b/rust-src/bch_bindgen/src/opts.rs
@@ -3,7 +3,33 @@ macro_rules! opt_set {
     ($opts:ident, $n:ident, $v:expr) => {
         bch_bindgen::paste! {
             $opts.$n = $v;
-            $opts.[<set_ $n _defined>](1);
+            $opts.[<set_ $n _defined>](1)
         }
-    }
+    };
+}
+
+#[macro_export]
+macro_rules! opt_defined {
+    ($opts:ident, $n:ident) => {
+        bch_bindgen::paste! {
+            $opts.[< $n _defined>]()
+        }
+    };
+}
+
+#[macro_export]
+macro_rules! opt_get {
+    ($opts:ident, $n:ident) => {
+        if bch_bindgen::opt_defined!($opts, $n) == 0 {
+            bch_bindgen::paste! {
+                unsafe {
+                    bch_bindgen::bcachefs::bch2_opts_default.$n
+                }
+            }
+        } else {
+            bch_bindgen::paste! {
+                $opts.$n
+            }
+        }
+    };
 }