fix(balloon): improve error message in case of too much requested memory

The balloon device always returns "Amount of pages requested cannot fit
in u32" even if it fails due to the guest memory check.

Reword the error to make it more clear.

Signed-off-by: Riccardo Mancini <[email protected]>

Author: Manciukic

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

@@ -41,7 +41,9 @@ const SIZE_OF_STAT: usize = std::mem::size_of::<BalloonStat>();
 fn mib_to_pages(amount_mib: u32) -> Result<u32, BalloonError> {
     amount_mib
         .checked_mul(MIB_TO_4K_PAGES)
-        .ok_or(BalloonError::TooManyPagesRequested)
+        .ok_or(BalloonError::TooMuchMemoryRequested(
+            u32::MAX / MIB_TO_4K_PAGES,
+        ))
 }
 
 fn pages_to_mib(amount_pages: u32) -> u32 {
@@ -455,7 +457,7 @@ impl Balloon {
             // The balloon cannot have a target size greater than the size of
             // the guest memory.
             if u64::from(amount_mib) > mem_size_mib(mem) {
-                return Err(BalloonError::TooManyPagesRequested);
+                return Err(BalloonError::TooMuchMemoryRequested(amount_mib));
             }
             self.config_space.num_pages = mib_to_pages(amount_mib)?;
             self.interrupt_trigger()

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

@@ -83,8 +83,8 @@ pub enum BalloonError {
     StatisticsDisabled,
     /// Statistics cannot be enabled/disabled after activation.
     StatisticsStateChange,
-    /// Amount of pages requested cannot fit in `u32`.
-    TooManyPagesRequested,
+    /// Requested memory should be less than {0}MiB
+    TooMuchMemoryRequested(u32),
     /// Error while processing the virt queues: {0}
     Queue(#[from] QueueError),
     /// {0}