xen: begin work on xen grant mappings

crates/xen/xengnt/src/error.rs

@@ -0,0 +1,13 @@
+use std::io;
+
+#[derive(thiserror::Error, Debug)]
+pub enum Error {
+    #[error("kernel error")]
+    Kernel(#[from] nix::errno::Errno),
+    #[error("io issue encountered")]
+    Io(#[from] io::Error),
+    #[error("failed to read structure")]
+    StructureReadFailed,
+}
+
+pub type Result<T> = std::result::Result<T, Error>;