errors: Improve error types and implement Debug

As our error types are enums, we can include the "source" error in our
later error types. This allows for more information when debugging
failures. To this end, we also implement Debug.

Signed-off-by: Joe Richey <joerichey@google.com>

Author: josephlr

src/bzimage.rs

@@ -14,16 +14,17 @@
 
 use crate::fat::{self, Read};
 
+#[derive(Debug)]
 pub enum Error {
-    FileError,
+    FileError(fat::Error),
     KernelOld,
     MagicMissing,
     NotRelocatable,
 }
 
 impl From<fat::Error> for Error {
-    fn from(_: fat::Error) -> Error {
-        Error::FileError
+    fn from(e: fat::Error) -> Error {
+        Error::FileError(e)
     }
 }
 
@@ -85,7 +86,7 @@ pub fn load_initrd(f: &mut dyn Read) -> Result<(), Error> {
             let mut data: [u8; 512] = [0; 512];
             match f.read(&mut data) {
                 Err(crate::fat::Error::EndOfFile) => break,
-                Err(_) => return Err(Error::FileError),
+                Err(e) => return Err(Error::FileError(e)),
                 Ok(_) => {}
             }
             let dst = initrd_region.as_mut_slice(u64::from(offset), u64::from(bytes_remaining));
@@ -96,7 +97,7 @@ pub fn load_initrd(f: &mut dyn Read) -> Result<(), Error> {
         let dst = initrd_region.as_mut_slice(u64::from(offset), 512);
         match f.read(dst) {
             Err(crate::fat::Error::EndOfFile) => break,
-            Err(_) => return Err(Error::FileError),
+            Err(e) => return Err(Error::FileError(e)),
             Ok(_) => {}
         }
 
@@ -202,7 +203,7 @@ pub fn load_kernel(f: &mut dyn Read) -> Result<u64, Error> {
                 // 0x200 is the startup_64 offset
                 return Ok(u64::from(KERNEL_LOCATION) + 0x200);
             }
-            Err(_) => return Err(Error::FileError),
+            Err(e) => return Err(Error::FileError(e)),
             Ok(_) => {}
         };
 

src/loader.rs

@@ -23,20 +23,21 @@ pub struct LoaderConfig {
     pub cmdline: [u8; 4096],
 }
 
+#[derive(Debug)]
 pub enum Error {
-    FileError,
-    BzImageError,
+    FileError(fat::Error),
+    BzImageError(bzimage::Error),
 }
 
 impl From<fat::Error> for Error {
-    fn from(_: fat::Error) -> Error {
-        Error::FileError
+    fn from(e: fat::Error) -> Error {
+        Error::FileError(e)
     }
 }
 
 impl From<bzimage::Error> for Error {
-    fn from(_: bzimage::Error) -> Error {
-        Error::BzImageError
+    fn from(e: bzimage::Error) -> Error {
+        Error::BzImageError(e)
     }
 }
 

src/virtio.rs

@@ -13,6 +13,7 @@
 // limitations under the License.
 
 /// Virtio related errors
+#[derive(Debug)]
 pub enum Error {
     VirtioUnsupportedDevice,
     VirtioLegacyOnly,