ci: Add integration test for virtio-rtc

Integration test for virtio-devices/src/rtc.rs. Requires that
the test kernel has the following configs:

CONFIG_PTP_1588_CLOCK=y
CONFIG_VIRTIO_RTC=y
CONFIG_VIRTIO_RTC_PTP=y

Signed-off-by: Cameron Baird <cameronbaird@microsoft.com>

cloud-hypervisor/tests/integration.rs

@@ -2091,6 +2091,70 @@ mod common_parallel {
         _test_virtio_fs(&prepare_virtiofsd, false, true, Some(15));
     }
 
+    #[test]
+    fn test_virtio_rtc() {
+        let disk_config = UbuntuDiskConfig::new(JAMMY_IMAGE_NAME.to_string());
+        let guest = Guest::new(Box::new(disk_config));
+
+        let kernel_path = direct_kernel_boot_path();
+
+        // virtio-rtc is disabled by default and needs to be explicitly enabled.
+        let mut child = GuestCommand::new(&guest)
+            .default_cpus()
+            .default_memory()
+            .args(["--kernel", kernel_path.to_str().unwrap()])
+            .args(["--cmdline", DIRECT_KERNEL_BOOT_CMDLINE])
+            .args(["--rtc"])
+            .default_disks()
+            .default_net()
+            .capture_output()
+            .spawn()
+            .unwrap();
+
+        let r = std::panic::catch_unwind(|| {
+            guest.wait_vm_boot().unwrap();
+
+            // Fail fast if the virtio-rtc driver is not loaded.
+            assert_eq!(
+                guest
+                    .ssh_command(
+                        "test -d /sys/bus/virtio/drivers/virtio_rtc && echo ok || echo missing"
+                    )
+                    .unwrap()
+                    .trim(),
+                "ok"
+            );
+
+            // Find the PTP device backed by virtio-rtc (clock_name starts with
+            // "Virtio PTP"), which may coexist with KVM's "KVM virtual PTP".
+            let ptp_dev = guest
+                .ssh_command(
+                    "for d in /sys/class/ptp/ptp*; do \
+                   if grep -q '^Virtio PTP' \"$d/clock_name\" 2>/dev/null; then \
+                     basename \"$d\"; break; \
+                   fi; \
+                 done",
+                )
+                .unwrap();
+            let ptp_dev = ptp_dev.trim();
+            assert!(ptp_dev.starts_with("ptp"), "No virtio-rtc PTP device found");
+
+            // Verify the device node exists
+            assert_eq!(
+                guest
+                    .ssh_command(&format!("ls /dev/{ptp_dev} 2>/dev/null || echo missing"))
+                    .unwrap()
+                    .trim(),
+                format!("/dev/{ptp_dev}")
+            );
+        });
+
+        kill_child(&mut child);
+        let output = child.wait_with_output().unwrap();
+
+        handle_child_output(r, &output);
+    }
+
     #[test]
     fn test_virtio_pmem_discard_writes() {
         test_virtio_pmem(true, false);