fix: driver-sys MsiAllocation type chain — alloc_cpu_id + u32 irq

Add missing alloc_cpu_id() function (atomic round-robin CPU selection).
Fix type chain: MsiAllocation.irq u8→u32 to match allocate_irq_vector
return type. irq_set_affinity accepts u32 irq for consistency.

Verified: driver-sys compiles on Linux (x86_64-unknown-linux-gnu).
Full redbear-mini image builds and boots in QEMU.

local/recipes/drivers/redox-driver-sys/source/src/irq.rs

@@ -288,6 +288,18 @@ fn read_cpu_count() -> Result<u8> {
     Ok(buf[0].max(1))
 }
 
+#[cfg(target_os = "redox")]
+fn alloc_cpu_id() -> u8 {
+    match read_cpu_count() {
+        Ok(n) if n > 0 => {
+            use std::sync::atomic::{AtomicU8, Ordering};
+            static NEXT: AtomicU8 = AtomicU8::new(0);
+            NEXT.fetch_add(1, Ordering::Relaxed) % n
+        }
+        _ => 0,
+    }
+}
+
 #[cfg(target_os = "redox")]
 fn allocate_irq_vector(cpu_id: u8) -> Result<(u32, File)> {
     let dir = format!("/scheme/irq/cpu-{cpu_id:02x}");
@@ -431,7 +443,7 @@ mod tests {
 /// Standard MSI (non-X) interrupt allocation.
 /// For devices that support MSI but not MSI-X.
 pub struct MsiAllocation {
-    pub irq: u8,
+    pub irq: u32,
     pub fd: crate::pci::IrqFd,
     pub vector_count: u8,
 }
@@ -439,7 +451,7 @@ pub struct MsiAllocation {
 impl MsiAllocation {
     #[cfg(target_os = "redox")]
     pub fn request(multiple_message_capable: u8, requested: u8) -> Result<Self> {
-        let cpu_id = alloc_cpu_id(0);
+        let cpu_id = alloc_cpu_id();
         let count = requested.min(1u8 << multiple_message_capable);
         let (irq, fd) = allocate_irq_vector(cpu_id)?;
         log::info!("redox-driver-sys: allocated MSI vector -> irq {} on cpu {}", irq, cpu_id);
@@ -455,7 +467,7 @@ impl MsiAllocation {
 /// Set IRQ affinity to a specific CPU.
 /// Returns true if the affinity was successfully changed.
 #[cfg(target_os = "redox")]
-pub fn irq_set_affinity(irq: u8, cpu_id: u32) -> Result<()> {
+pub fn irq_set_affinity(irq: u32, cpu_id: u32) -> Result<()> {
     use std::io::Write;
     let path = format!("/scheme/irq/{}/affinity", irq);
     let mut f = std::fs::OpenOptions::new().write(true).open(&path)
@@ -465,6 +477,6 @@ pub fn irq_set_affinity(irq: u8, cpu_id: u32) -> Result<()> {
 }
 
 #[cfg(not(target_os = "redox"))]
-pub fn irq_set_affinity(_irq: u8, _cpu_id: u32) -> Result<()> {
+pub fn irq_set_affinity(_irq: u32, _cpu_id: u32) -> Result<()> {
     Err(DriverError::Irq("IRQ affinity is only available on target_os=redox".into()))
 }