virtio: vhost: user: remove Error type parameter for VhostUserBackend

This type is never set to anything else than `anyhow::Error` and makes
it harder to work with VhostUserBackends as trait objects.

BUG=b:217480043
TEST=cargo build

Change-Id: Iae0be59f9b2bcec1e3fe9b22cbec2f9b99a59020
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3702776
Tested-by: kokoro <noreply+kokoro@google.com>
Commit-Queue: Alexandre Courbot <acourbot@chromium.org>
Reviewed-by: Keiichi Watanabe <keiichiw@chromium.org>
Reviewed-by: Morg <morg@chromium.org>

devices/src/virtio/vhost/user/device/block.rs

@@ -130,8 +130,6 @@ impl VhostUserBackend for BlockBackend {
     const MAX_QUEUE_NUM: usize = NUM_QUEUES as usize;
     const MAX_VRING_LEN: u16 = QUEUE_SIZE;
 
-    type Error = anyhow::Error;
-
     fn features(&self) -> u64 {
         self.avail_features
     }

devices/src/virtio/vhost/user/device/console.rs

@@ -237,8 +237,6 @@ impl VhostUserBackend for ConsoleBackend {
     const MAX_QUEUE_NUM: usize = 2; /* transmit and receive queues */
     const MAX_VRING_LEN: u16 = 256;
 
-    type Error = anyhow::Error;
-
     fn features(&self) -> u64 {
         self.device.avail_features
     }

devices/src/virtio/vhost/user/device/cras_snd.rs

@@ -91,8 +91,6 @@ impl VhostUserBackend for CrasSndBackend {
     const MAX_QUEUE_NUM: usize = MAX_QUEUE_NUM;
     const MAX_VRING_LEN: u16 = MAX_VRING_LEN;
 
-    type Error = anyhow::Error;
-
     fn features(&self) -> u64 {
         self.avail_features
     }

devices/src/virtio/vhost/user/device/fs.rs

@@ -104,8 +104,6 @@ impl VhostUserBackend for FsBackend {
     const MAX_QUEUE_NUM: usize = 2; /* worker queue and high priority queue */
     const MAX_VRING_LEN: u16 = 1024;
 
-    type Error = anyhow::Error;
-
     fn features(&self) -> u64 {
         self.avail_features
     }

devices/src/virtio/vhost/user/device/gpu.rs

@@ -151,8 +151,6 @@ impl VhostUserBackend for GpuBackend {
     const MAX_QUEUE_NUM: usize = gpu::QUEUE_SIZES.len();
     const MAX_VRING_LEN: u16 = gpu::QUEUE_SIZES[0];
 
-    type Error = anyhow::Error;
-
     fn features(&self) -> u64 {
         self.gpu.borrow().features() | VhostUserVirtioFeatures::PROTOCOL_FEATURES.bits()
     }

devices/src/virtio/vhost/user/device/handler.rs

@@ -155,19 +155,15 @@ pub fn create_guest_memory(
 pub trait VhostUserBackend
 where
     Self: Sized,
-    Self::Error: std::fmt::Display,
 {
     const MAX_QUEUE_NUM: usize;
     const MAX_VRING_LEN: u16;
 
-    /// Error type specific to this backend.
-    type Error;
-
     /// The set of feature bits that this backend supports.
     fn features(&self) -> u64;
 
     /// Acknowledges that this set of features should be enabled.
-    fn ack_features(&mut self, value: u64) -> std::result::Result<(), Self::Error>;
+    fn ack_features(&mut self, value: u64) -> anyhow::Result<()>;
 
     /// Returns the set of enabled features.
     fn acked_features(&self) -> u64;
@@ -176,7 +172,7 @@ where
     fn protocol_features(&self) -> VhostUserProtocolFeatures;
 
     /// Acknowledges that this set of protocol features should be enabled.
-    fn ack_protocol_features(&mut self, _value: u64) -> std::result::Result<(), Self::Error>;
+    fn ack_protocol_features(&mut self, _value: u64) -> anyhow::Result<()>;
 
     /// Returns the set of enabled protocol features.
     fn acked_protocol_features(&self) -> u64;
@@ -188,10 +184,7 @@ where
     fn write_config(&self, _offset: u64, _data: &[u8]) {}
 
     /// Sets the channel for device-specific communication.
-    fn set_device_request_channel(
-        &mut self,
-        _channel: File,
-    ) -> std::result::Result<(), Self::Error> {
+    fn set_device_request_channel(&mut self, _channel: File) -> anyhow::Result<()> {
         Ok(())
     }
 
@@ -205,7 +198,7 @@ where
         mem: GuestMemory,
         doorbell: Arc<Mutex<Doorbell>>,
         kick_evt: Event,
-    ) -> std::result::Result<(), Self::Error>;
+    ) -> anyhow::Result<()>;
 
     /// Indicates that the backend should stop processing requests for virtio queue number `idx`.
     fn stop_queue(&mut self, idx: usize);
@@ -697,13 +690,11 @@ mod tests {
         const MAX_QUEUE_NUM: usize = 16;
         const MAX_VRING_LEN: u16 = 256;
 
-        type Error = anyhow::Error;
-
         fn features(&self) -> u64 {
             self.avail_features
         }
 
-        fn ack_features(&mut self, value: u64) -> std::result::Result<(), Self::Error> {
+        fn ack_features(&mut self, value: u64) -> anyhow::Result<()> {
             let unrequested_features = value & !self.avail_features;
             if unrequested_features != 0 {
                 bail!(
@@ -723,7 +714,7 @@ mod tests {
             VhostUserProtocolFeatures::CONFIG
         }
 
-        fn ack_protocol_features(&mut self, features: u64) -> std::result::Result<(), Self::Error> {
+        fn ack_protocol_features(&mut self, features: u64) -> anyhow::Result<()> {
             let features = VhostUserProtocolFeatures::from_bits(features).ok_or(anyhow!(
                 "invalid protocol features are given: 0x{:x}",
                 features
@@ -750,7 +741,7 @@ mod tests {
             _mem: GuestMemory,
             _doorbell: Arc<Mutex<Doorbell>>,
             _kick_evt: Event,
-        ) -> std::result::Result<(), Self::Error> {
+        ) -> anyhow::Result<()> {
             Ok(())
         }
 

devices/src/virtio/vhost/user/device/net.rs

@@ -105,8 +105,6 @@ where
     const MAX_QUEUE_NUM: usize = MAX_QUEUE_NUM; /* rx, tx, ctrl */
     const MAX_VRING_LEN: u16 = MAX_VRING_LEN;
 
-    type Error = anyhow::Error;
-
     fn features(&self) -> u64 {
         self.avail_features
     }

devices/src/virtio/vhost/user/device/wl.rs

@@ -116,8 +116,6 @@ impl VhostUserBackend for WlBackend {
     const MAX_QUEUE_NUM: usize = wl::QUEUE_SIZES.len();
     const MAX_VRING_LEN: u16 = wl::QUEUE_SIZE;
 
-    type Error = anyhow::Error;
-
     fn features(&self) -> u64 {
         self.features
     }