virtio-devices: Factor out NEEDS_RESET helpers

Both block and net implement the same DEVICE_NEEDS_RESET bookkeeping
when a corrupted virtqueue request is detected. They set the bit,
trigger a config change interrupt and log a warning. Move that logic
into shared device_needs_reset and mark_device_needs_reset helpers in
lib.rs and update both call sites to use them.

No functional change.

Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>

virtio-devices/src/lib.rs

@@ -11,6 +11,7 @@
 //! Implements virtio devices, queues, and transport mechanisms.
 
 use std::io;
+use std::sync::atomic::{AtomicU8, Ordering};
 
 use serde::{Deserialize, Serialize};
 use thiserror::Error;
@@ -69,6 +70,33 @@ const DEVICE_FEATURES_OK: u32 = 0x08;
 const DEVICE_NEEDS_RESET: u32 = 0x40;
 const DEVICE_FAILED: u32 = 0x80;
 
+/// Returns true if `device_status` has the `DEVICE_NEEDS_RESET` bit set.
+pub(crate) fn device_needs_reset(device_status: &AtomicU8) -> bool {
+    (device_status.load(Ordering::Acquire) & DEVICE_NEEDS_RESET as u8) != 0
+}
+
+/// Marks a virtio device as `NEEDS_RESET` and notifies the guest via a config
+/// change interrupt. Used when a guest induced error (corrupted virtqueue,
+/// malformed descriptor chain or similar) is detected and the device wants
+/// to stop further queue processing without killing the worker thread.
+///
+/// `context` is included verbatim in the warning log to identify the cause.
+pub(crate) fn mark_device_needs_reset(
+    device_status: &AtomicU8,
+    interrupt_cb: &dyn self::VirtioInterrupt,
+    context: std::fmt::Arguments<'_>,
+) {
+    log::warn!(
+        "Corrupted request detected ({context}). Setting device status to 'NEEDS_RESET' and stopping processing queues until reset."
+    );
+
+    device_status.fetch_or(DEVICE_NEEDS_RESET as u8, Ordering::SeqCst);
+
+    if let Err(e) = interrupt_cb.trigger(self::VirtioInterruptType::Config) {
+        log::error!("Failed to signal config interrupt: {e:?}");
+    }
+}
+
 const VIRTIO_F_RING_INDIRECT_DESC: u32 = 28;
 const VIRTIO_F_RING_EVENT_IDX: u32 = 29;
 const VIRTIO_F_VERSION_1: u32 = 32;