Rust: Start of cmd_list rewrite

This is a _very_ preliminary rewrite of the cmd_list tool in rust, which
is intended to be a testing ground for a safe interface in Rust to the
core btree interface. This adds rust wrappers for:

bch_fs:		provides bch2_fs_open(), bch2_fs_stop
btree_trans:	provides bch2_trans_init(), bch2_trans_exit()
btree_iter:	provides peek, peek_and_restart, advance
bch_errcode:	implements Display (wraps bch2_err_str())
bpos:		implements Ord (wraps bpos_cmp())
bkey_s_c:	implements Display (wraps bch2_bkey_val_to_text())

and other assorted types.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

1 files changed, 40 insertions, 0 deletions

diff --git a/rust-src/bch_bindgen/src/errcode.rs b/rust-src/bch_bindgen/src/errcode.rs
new file mode 100644
index 00000000..4d75f1d2
--- /dev/null
+++ b/rust-src/bch_bindgen/src/errcode.rs
@@ -0,0 +1,40 @@
+use crate::bcachefs;
+use std::ffi::CStr;
+use std::fmt;
+
+pub use crate::c::bch_errcode;
+
+impl fmt::Display for bch_errcode {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        let s = unsafe { CStr::from_ptr(bcachefs::bch2_err_str(*self as i32)) };
+        write!(f, "{:?}", s)
+    }
+}
+
+/* Can we make a function generic over ptr constness? */
+
+pub fn errptr_to_result<T>(p: *mut T) -> Result<*mut T, bch_errcode> {
+    let addr = p as usize;
+    let max_err: isize = -4096;
+    if addr > max_err as usize {
+        let addr = addr as i32;
+        let err: bch_errcode = unsafe { std::mem::transmute(-addr) };
+        Err(err)
+    } else {
+        Ok(p)
+    }
+}
+
+pub fn errptr_to_result_c<T>(p: *const T) -> Result<*const T, bch_errcode> {
+    let addr = p as usize;
+    let max_err: isize = -4096;
+    if addr > max_err as usize {
+        let addr = addr as i32;
+        let err: bch_errcode = unsafe { std::mem::transmute(-addr) };
+        Err(err)
+    } else {
+        Ok(p)
+    }
+}
+
+impl std::error::Error for bch_errcode {}