refactor: Cleanuo Balloon error

Add from #[from] annotation to avoid map_err() calls, and delete unused
variants.

Signed-off-by: Patrick Roy <roypat@amazon.co.uk>

Author: roypat

src/vmm/src/devices/virtio/balloon/device.rs

@@ -339,7 +339,7 @@ impl Balloon {
 
                 // Acknowledge the receipt of the descriptor.
                 // 0 is number of bytes the device has written to memory.
-                queue.add_used(head.index, 0).map_err(BalloonError::Queue)?;
+                queue.add_used(head.index, 0)?;
                 needs_interrupt = true;
             }
 
@@ -376,7 +376,7 @@ impl Balloon {
         let mut needs_interrupt = false;
 
         while let Some(head) = queue.pop() {
-            queue.add_used(head.index, 0).map_err(BalloonError::Queue)?;
+            queue.add_used(head.index, 0)?;
             needs_interrupt = true;
         }
 
@@ -397,9 +397,7 @@ impl Balloon {
                 // We shouldn't ever have an extra buffer if the driver follows
                 // the protocol, but return it if we find one.
                 error!("balloon: driver is not compliant, more than one stats buffer received");
-                self.queues[STATS_INDEX]
-                    .add_used(prev_stats_desc, 0)
-                    .map_err(BalloonError::Queue)?;
+                self.queues[STATS_INDEX].add_used(prev_stats_desc, 0)?;
             }
             for index in (0..head.len).step_by(SIZE_OF_STAT) {
                 // Read the address at position `index`. The only case
@@ -447,9 +445,7 @@ impl Balloon {
         // The communication is driven by the device by using the buffer
         // and sending a used buffer notification
         if let Some(index) = self.stats_desc_index.take() {
-            self.queues[STATS_INDEX]
-                .add_used(index, 0)
-                .map_err(BalloonError::Queue)?;
+            self.queues[STATS_INDEX].add_used(index, 0)?;
             self.signal_used_queue()
         } else {
             error!("Failed to update balloon stats, missing descriptor.");

src/vmm/src/devices/virtio/balloon/mod.rs

@@ -11,7 +11,6 @@ pub mod test_utils;
 mod util;
 
 use log::error;
-use vm_memory::GuestMemoryError;
 
 pub use self::device::{Balloon, BalloonConfig, BalloonStats};
 use super::queue::QueueError;
@@ -68,16 +67,12 @@ const VIRTIO_BALLOON_S_HTLB_PGFAIL: u16 = 9;
 /// Balloon device related errors.
 #[derive(Debug, thiserror::Error, displaydoc::Display)]
 pub enum BalloonError {
-    /// Activation error: {0}
-    Activate(super::ActivateError),
     /// No balloon device found.
     DeviceNotFound,
     /// Device not activated yet.
     DeviceNotActive,
     /// EventFd error: {0}
     EventFd(std::io::Error),
-    /// Guest gave us bad memory addresses: {0}
-    GuestMemory(GuestMemoryError),
     /// Received error while sending an interrupt: {0}
     InterruptError(std::io::Error),
     /// Guest gave us a malformed descriptor.
@@ -93,9 +88,7 @@ pub enum BalloonError {
     /// Amount of pages requested cannot fit in `u32`.
     TooManyPagesRequested,
     /// Error while processing the virt queues: {0}
-    Queue(QueueError),
-    /// Error removing a memory region at inflate time: {0}
-    RemoveMemoryRegion(RemoveRegionError),
+    Queue(#[from] QueueError),
     /// Error creating the statistics timer: {0}
     Timer(std::io::Error),
 }