fix: add try_port() to PciBar and try_irq_handle() to LegacyInterruptLine

Non-panicking variants needed by ac97d, vboxd, and other drivers that
prefer error handling over panics.

drivers/pcid/src/driver_interface/bar.rs

@@ -65,4 +65,14 @@ impl PciBar {
             _ => None,
         }
     }
+
+    pub fn try_port(&self) -> Result<u16, &'static str> {
+        match *self {
+            PciBar::Port(port) => Ok(port),
+            PciBar::Memory32 { .. } | PciBar::Memory64 { .. } => {
+                Err("expected port BAR, found memory BAR")
+            }
+            PciBar::None => Err("expected BAR to exist"),
+        }
+    }
 }

drivers/pcid/src/driver_interface/mod.rs

@@ -50,6 +50,29 @@ impl LegacyInterruptLine {
                 .unwrap_or_else(|err| panic!("{driver}: failed to open IRQ file: {err}"))
         }
     }
+
+    /// Non-panicking version of `irq_handle`.
+    pub fn try_irq_handle(self, _driver: &str) -> io::Result<File> {
+        if let Some((phandle, addr, cells)) = self.phandled {
+            let path = match cells {
+                1 => format!("/scheme/irq/phandle-{}/{}", phandle, addr[0]),
+                2 => format!("/scheme/irq/phandle-{}/{},{}", phandle, addr[0], addr[1]),
+                3 => format!(
+                    "/scheme/irq/phandle-{}/{},{},{}",
+                    phandle, addr[0], addr[1], addr[2]
+                ),
+                _ => {
+                    return Err(io::Error::new(
+                        io::ErrorKind::InvalidInput,
+                        format!("unexpected IRQ cells count: {cells}"),
+                    ))
+                }
+            };
+            File::create(path)
+        } else {
+            File::open(format!("/scheme/irq/{}", self.irq))
+        }
+    }
 }
 
 impl fmt::Display for LegacyInterruptLine {