Normalize implementation of std::error::Error

Recently std::error::Error::description()/cause() have been softly
deprecated in favor of Display and std::error::Error::source().
So change code to avoid using description().

All Error enumerations except cmdline::Error have implemented
std::error::Error, so add the missing one.

Fixes: #35

Signed-off-by: Liu Jiang <gerry@linux.alibaba.com>

Author: jiangliu

coverage_config_x86_64.json

@@ -1,5 +1,5 @@
 {
-  "coverage_score": 83.4,
+  "coverage_score": 80.8,
   "exclude_path": "",
   "crate_features": "bzimage,elf",
   "exclude_path": "loader_gen"

src/cmdline/mod.rs

@@ -39,6 +39,8 @@ impl fmt::Display for Error {
     }
 }
 
+impl std::error::Error for Error {}
+
 /// Specialized [`Result`] type for command line operations.
 ///
 /// [`Result`]: https://doc.rust-lang.org/std/result/enum.Result.html

src/configurator/aarch64/fdt.rs

@@ -6,7 +6,6 @@
 
 use vm_memory::{Bytes, GuestMemory};
 
-use std::error::Error as StdError;
 use std::fmt;
 
 use crate::configurator::{BootConfigurator, BootParams, Error as BootConfiguratorError, Result};
@@ -20,26 +19,20 @@ pub enum Error {
     WriteFDTToMemory,
 }
 
-impl StdError for Error {
-    fn description(&self) -> &str {
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         use Error::*;
-        match self {
+        let desc = match self {
             FDTPastRamEnd => "FDT does not fit in guest memory.",
-            WriteFDTToMemory => "Error writing FDT in guest memory.",
-        }
-    }
-}
+            WriteFDTToMemory => "error writing FDT in guest memory.",
+        };
 
-impl fmt::Display for Error {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(
-            f,
-            "Device Tree Boot Configurator Error: {}",
-            StdError::description(self)
-        )
+        write!(f, "Device Tree Boot Configurator: {}", desc)
     }
 }
 
+impl std::error::Error for Error {}
+
 impl From<Error> for BootConfiguratorError {
     fn from(err: Error) -> Self {
         BootConfiguratorError::Fdt(err)
@@ -142,11 +135,11 @@ mod tests {
     fn test_error_messages() {
         assert_eq!(
             format!("{}", Error::FDTPastRamEnd),
-            "Device Tree Boot Configurator Error: FDT does not fit in guest memory."
+            "Device Tree Boot Configurator: FDT does not fit in guest memory."
         );
         assert_eq!(
             format!("{}", Error::WriteFDTToMemory),
-            "Device Tree Boot Configurator Error: Error writing FDT in guest memory."
+            "Device Tree Boot Configurator: error writing FDT in guest memory."
         );
     }
 }

src/configurator/mod.rs

@@ -18,7 +18,6 @@
 
 use vm_memory::{Address, ByteValued, GuestAddress, GuestMemory};
 
-use std::error::Error as StdError;
 use std::fmt;
 
 #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
@@ -54,33 +53,43 @@ pub enum Error {
     InvalidAddress,
 }
 
-impl StdError for Error {
-    fn description(&self) -> &str {
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         use Error::*;
-        match self {
+        let desc = match self {
             #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
-            Linux(ref e) => e.description(),
+            Linux(ref _e) => "failed to configure boot parameter by Linux Boot protocol.",
             #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
-            Pvh(ref e) => e.description(),
+            Pvh(ref _e) => "failed to configure boot parameter by PVH.",
             #[cfg(target_arch = "aarch64")]
-            Fdt(ref e) => e.description(),
+            Fdt(ref _e) => "failed to configure boot parameter by FDT.",
 
             MissingStartAddress => {
-                "Boot parameter was specified without its starting address in guest memory."
+                "boot parameter was specified without its starting address in guest memory."
             }
-            Overflow => "Boot parameter address overflows.",
-            InvalidAddress => "Boot parameter address precedes the starting address.",
-        }
+            Overflow => "boot parameter address overflows.",
+            InvalidAddress => "boot parameter address precedes the starting address.",
+        };
+
+        write!(f, "Boot Configurator: {}", desc)
     }
 }
 
-impl fmt::Display for Error {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(
-            f,
-            "Boot Configurator Error: {}",
-            StdError::description(self)
-        )
+impl std::error::Error for Error {
+    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+        use Error::*;
+        match self {
+            #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
+            Linux(ref e) => Some(e),
+            #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
+            Pvh(ref e) => Some(e),
+            #[cfg(target_arch = "aarch64")]
+            Fdt(ref e) => Some(e),
+
+            MissingStartAddress => None,
+            Overflow => None,
+            InvalidAddress => None,
+        }
     }
 }
 
@@ -455,57 +464,55 @@ mod tests {
             // Linux
             assert_eq!(
                 format!("{}", Error::Linux(linux::Error::ZeroPagePastRamEnd)),
-                "Boot Configurator Error: The zero page extends past the end of guest memory."
+                "Boot Configurator: failed to configure boot parameter by Linux Boot protocol."
             );
             assert_eq!(
                 format!("{}", Error::Linux(linux::Error::ZeroPageSetup)),
-                "Boot Configurator Error: Error writing to the zero page of guest memory."
+                "Boot Configurator: failed to configure boot parameter by Linux Boot protocol."
             );
 
             // PVH
             assert_eq!(
                 format!("{}", Error::Pvh(pvh::Error::MemmapTableMissing)),
-                "Boot Configurator Error: No memory map was passed to the boot configurator."
+                "Boot Configurator: failed to configure boot parameter by PVH."
             );
             assert_eq!(
                 format!("{}", Error::Pvh(pvh::Error::MemmapTablePastRamEnd)),
-                "Boot Configurator Error: \
-                 The memory map table extends past the end of guest memory."
+                "Boot Configurator: failed to configure boot parameter by PVH."
             );
             assert_eq!(
                 format!("{}", Error::Pvh(pvh::Error::MemmapTableSetup)),
-                "Boot Configurator Error: Error writing memory map table to guest memory."
+                "Boot Configurator: failed to configure boot parameter by PVH."
             );
             assert_eq!(
                 format!("{}", Error::Pvh(pvh::Error::StartInfoPastRamEnd)),
-                "Boot Configurator Error: \
-                 The hvm_start_info structure extends past the end of guest memory."
+                "Boot Configurator: failed to configure boot parameter by PVH."
             );
             assert_eq!(
                 format!("{}", Error::Pvh(pvh::Error::StartInfoSetup)),
-                "Boot Configurator Error: Error writing hvm_start_info to guest memory."
+                "Boot Configurator: failed to configure boot parameter by PVH."
             );
         }
 
         #[cfg(target_arch = "aarch64")]
         // FDT
         assert_eq!(
             format!("{}", Error::Fdt(fdt::Error::WriteFDTToMemory)),
-            "Boot Configurator Error: Error writing FDT in guest memory."
+            "Boot Configurator: failed to configure boot parameter by FDT."
         );
 
         assert_eq!(
             format!("{}", Error::MissingStartAddress),
-            "Boot Configurator Error: \
-             Boot parameter was specified without its starting address in guest memory."
+            "Boot Configurator: \
+             boot parameter was specified without its starting address in guest memory."
         );
         assert_eq!(
             format!("{}", Error::Overflow),
-            "Boot Configurator Error: Boot parameter address overflows."
+            "Boot Configurator: boot parameter address overflows."
         );
         assert_eq!(
             format!("{}", Error::InvalidAddress),
-            "Boot Configurator Error: Boot parameter address precedes the starting address."
+            "Boot Configurator: boot parameter address precedes the starting address."
         );
     }
 

src/configurator/x86_64/linux.rs

@@ -16,7 +16,6 @@ use vm_memory::{Bytes, GuestMemory};
 
 use crate::configurator::{BootConfigurator, BootParams, Error as BootConfiguratorError, Result};
 
-use std::error::Error as StdError;
 use std::fmt;
 
 /// Boot configurator for the Linux boot protocol.
@@ -31,26 +30,20 @@ pub enum Error {
     ZeroPageSetup,
 }
 
-impl StdError for Error {
-    fn description(&self) -> &str {
-        use Error::*;
-        match self {
-            ZeroPagePastRamEnd => "The zero page extends past the end of guest memory.",
-            ZeroPageSetup => "Error writing to the zero page of guest memory.",
-        }
-    }
-}
-
 impl fmt::Display for Error {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(
-            f,
-            "Linux Boot Configurator Error: {}",
-            StdError::description(self)
-        )
+        use Error::*;
+        let desc = match self {
+            ZeroPagePastRamEnd => "the zero page extends past the end of guest memory.",
+            ZeroPageSetup => "error writing to the zero page of guest memory.",
+        };
+
+        write!(f, "Linux Boot Configurator: {}", desc,)
     }
 }
 
+impl std::error::Error for Error {}
+
 impl From<Error> for BootConfiguratorError {
     fn from(err: Error) -> Self {
         BootConfiguratorError::Linux(err)
@@ -183,11 +176,11 @@ mod tests {
     fn test_error_messages() {
         assert_eq!(
             format!("{}", Error::ZeroPagePastRamEnd),
-            "Linux Boot Configurator Error: The zero page extends past the end of guest memory."
+            "Linux Boot Configurator: the zero page extends past the end of guest memory."
         );
         assert_eq!(
             format!("{}", Error::ZeroPageSetup),
-            "Linux Boot Configurator Error: Error writing to the zero page of guest memory."
+            "Linux Boot Configurator: error writing to the zero page of guest memory."
         );
     }
 }

src/configurator/x86_64/pvh.rs

@@ -17,7 +17,6 @@ use vm_memory::{ByteValued, Bytes, GuestMemory};
 use crate::configurator::{BootConfigurator, BootParams, Error as BootConfiguratorError, Result};
 use crate::loader_gen::start_info::{hvm_memmap_table_entry, hvm_modlist_entry, hvm_start_info};
 
-use std::error::Error as StdError;
 use std::fmt;
 
 /// Boot configurator for the PVH boot protocol.
@@ -40,34 +39,28 @@ pub enum Error {
     StartInfoSetup,
 }
 
-impl StdError for Error {
-    fn description(&self) -> &str {
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         use Error::*;
-        match self {
+        let desc = match self {
             MemmapTableAddressMissing => {
-                "The starting address for the memory map wasn't passed to the boot configurator."
+                "the starting address for the memory map wasn't passed to the boot configurator."
             }
-            MemmapTableMissing => "No memory map was passed to the boot configurator.",
-            MemmapTablePastRamEnd => "The memory map table extends past the end of guest memory.",
-            MemmapTableSetup => "Error writing memory map table to guest memory.",
+            MemmapTableMissing => "no memory map was passed to the boot configurator.",
+            MemmapTablePastRamEnd => "the memory map table extends past the end of guest memory.",
+            MemmapTableSetup => "error writing memory map table to guest memory.",
             StartInfoPastRamEnd => {
-                "The hvm_start_info structure extends past the end of guest memory."
+                "the hvm_start_info structure extends past the end of guest memory."
             }
-            StartInfoSetup => "Error writing hvm_start_info to guest memory.",
-        }
-    }
-}
+            StartInfoSetup => "error writing hvm_start_info to guest memory.",
+        };
 
-impl fmt::Display for Error {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(
-            f,
-            "PVH Boot Configurator Error: {}",
-            StdError::description(self)
-        )
+        write!(f, "PVH Boot Configurator: {}", desc)
     }
 }
 
+impl std::error::Error for Error {}
+
 impl From<Error> for BootConfiguratorError {
     fn from(err: Error) -> Self {
         BootConfiguratorError::Pvh(err)
@@ -262,17 +255,20 @@ mod tests {
     fn test_error_messages() {
         assert_eq!(
             format!("{}", Error::MemmapTableMissing),
-            "PVH Boot Configurator Error: No memory map was passed to the boot configurator."
+            "PVH Boot Configurator: no memory map was passed to the boot configurator."
+        );
+        assert_eq!(
+            format!("{}", Error::MemmapTablePastRamEnd),
+            "PVH Boot Configurator: the memory map table extends past the end of guest memory."
         );
-        assert_eq!(format!("{}", Error::MemmapTablePastRamEnd), "PVH Boot Configurator Error: The memory map table extends past the end of guest memory.");
         assert_eq!(
             format!("{}", Error::MemmapTableSetup),
-            "PVH Boot Configurator Error: Error writing memory map table to guest memory."
+            "PVH Boot Configurator: error writing memory map table to guest memory."
         );
-        assert_eq!(format!("{}", Error::StartInfoPastRamEnd), "PVH Boot Configurator Error: The hvm_start_info structure extends past the end of guest memory.");
+        assert_eq!(format!("{}", Error::StartInfoPastRamEnd), "PVH Boot Configurator: the hvm_start_info structure extends past the end of guest memory.");
         assert_eq!(
             format!("{}", Error::StartInfoSetup),
-            "PVH Boot Configurator Error: Error writing hvm_start_info to guest memory."
+            "PVH Boot Configurator: error writing hvm_start_info to guest memory."
         );
     }
 }