Make qemu debug port output configurable

bin/propolis-server/src/lib/initializer.rs

@@ -267,6 +267,7 @@ impl<'a> MachineInitializer<'a> {
     }
 
     pub fn initialize_qemu_debug_port(&self) -> Result<(), Error> {
+        // TODO: Make the output file configurable
         let dbg = QemuDebugPort::create(&self.machine.bus_pio);
         let debug_file = std::fs::File::create("debug.out")?;
         let poller = chardev::BlockingFileOutput::new(debug_file);

bin/propolis-standalone/README.md

@@ -16,6 +16,8 @@ name = "testvm"
 cpus = 4
 bootrom = "/path/to/bootrom/OVMF_CODE.fd"
 memory = 1024
+# File path to store qemu debug port output (optional)
+# qemu_debug_file = "/path/to/output"
 
 [block_dev.alpine_iso]
 type = "file"

bin/propolis-standalone/src/main.rs

@@ -834,10 +834,20 @@ fn setup_instance(
     ps2_ctrl.attach(pio, chipset.as_ref());
     inv.register(&ps2_ctrl)?;
 
-    let debug_file = std::fs::File::create("debug.out")?;
-    let debug_out = chardev::BlockingFileOutput::new(debug_file);
+    // Qemu debug IO port
     let debug_device = hw::qemu::debug::QemuDebugPort::create(pio);
-    debug_out.attach(Arc::clone(&debug_device) as Arc<dyn BlockingSource>);
+    match &config.main.qemu_debug_file {
+        Some(path) => {
+            let debug_file = std::fs::File::create(path)?;
+            let debug_out = chardev::BlockingFileOutput::new(debug_file);
+            debug_out
+                .attach(Arc::clone(&debug_device) as Arc<dyn BlockingSource>);
+        }
+        None => {
+            // Send output bytes to the bit bucket
+            debug_device.set_consumer(Some(chardev::null_blocking_consumer()));
+        }
+    };
     inv.register(&debug_device)?;
 
     for (name, dev) in config.devices.iter() {

crates/propolis-standalone-config/src/lib.rs

@@ -3,6 +3,7 @@
 // file, You can obtain one at https://mozilla.org/MPL/2.0/.
 
 use std::collections::BTreeMap;
+use std::path::PathBuf;
 
 use serde::{Deserialize, Serialize};
 use strum::FromRepr;
@@ -50,6 +51,7 @@ pub struct Main {
     pub bootrom: String,
     pub memory: usize,
     pub use_reservoir: Option<bool>,
+    pub qemu_debug_file: Option<PathBuf>,
     pub cpuid_profile: Option<String>,
 }
 

lib/propolis/src/chardev/mod.rs

@@ -105,3 +105,10 @@ impl ConsumerCell {
         }
     }
 }
+
+/// Build a [`BlockingSourceConsumer`] which silently consumes any output bytes
+pub fn null_blocking_consumer() -> BlockingSourceConsumer {
+    Box::new(|_buf| {
+        // Simply do nothing with the buffer
+    })
+}