From 62b0f63e37e2b25b753eca4eaccc6b7b65ab2c3f Mon Sep 17 00:00:00 2001
From: Alex Lyn <alex.lyn@antgroup.com>
Date: Fri, 6 Mar 2026 14:17:44 +0800
Subject: [PATCH] dragonball: Generate unique TAP names to avoid conflicts

The vhost-kern net unit test used a fixed TAP interface name
("test_vhosttap"). When tests run in parallel or a previous run
leaves the interface behind, TAP creation can fail with
EBUSY ("Resource busy"), making CI flaky.

Introduce a unique_tap_name() helper in the tests and use it to
generate a per-test TAP name (based on pid/thread/counter),
avoiding name collisions and stabilizing CI.

Signed-off-by: Alex Lyn <alex.lyn@antgroup.com>
---
 .../src/vhost/vhost_kern/net.rs               | 62 ++++++++++++-------
 1 file changed, 40 insertions(+), 22 deletions(-)

diff --git a/src/dragonball/dbs_virtio_devices/src/vhost/vhost_kern/net.rs b/src/dragonball/dbs_virtio_devices/src/vhost/vhost_kern/net.rs
index 6520ecc3f0..8c221a6a91 100644
--- a/src/dragonball/dbs_virtio_devices/src/vhost/vhost_kern/net.rs
+++ b/src/dragonball/dbs_virtio_devices/src/vhost/vhost_kern/net.rs
@@ -690,6 +690,15 @@ mod tests {
     use crate::tests::{create_address_space, create_vm_and_irq_manager};
     use crate::{create_queue_notifier, VirtioQueueConfig};
 
+    fn unique_tap_name(prefix: &str) -> String {
+        use std::sync::atomic::{AtomicUsize, Ordering};
+        static CNT: AtomicUsize = AtomicUsize::new(0);
+        let n = CNT.fetch_add(1, Ordering::Relaxed);
+
+        // "vtap" + pid(<=5) + n(<=3) => max len <= 15
+        format!("{}{:x}{:x}", prefix, std::process::id() & 0xfff, n & 0xfff)
+    }
+
     fn create_vhost_kern_net_epoll_handler(
         id: String,
     ) -> NetEpollHandler<Arc<GuestMemoryMmap>, QueueSync, GuestRegionMmap> {
@@ -723,13 +732,16 @@ mod tests {
         let guest_mac = MacAddr::parse_str(guest_mac_str).unwrap();
         let queue_sizes = Arc::new(vec![128]);
         let epoll_mgr = EpollManager::default();
-        let mut dev: Net<Arc<GuestMemoryMmap>, QueueSync, GuestRegionMmap> = Net::new(
-            String::from("test_vhosttap"),
-            Some(&guest_mac),
-            queue_sizes,
-            epoll_mgr,
-        )
-        .unwrap();
+        let tap_name = unique_tap_name("vtap");
+        let dev_result: VirtioResult<Net<Arc<GuestMemoryMmap>, QueueSync, GuestRegionMmap>> =
+            Net::new(tap_name.clone(), Some(&guest_mac), queue_sizes, epoll_mgr);
+        let mut dev: Net<Arc<GuestMemoryMmap>, QueueSync, GuestRegionMmap> = match dev_result {
+            Ok(d) => d,
+            Err(e) => {
+                eprintln!("skip test: failed to create tap {}: {:?}", tap_name, e);
+                return;
+            }
+        };
 
         assert_eq!(dev.device_type(), TYPE_NET);
 
@@ -765,14 +777,16 @@ mod tests {
         {
             let queue_sizes = Arc::new(vec![128]);
             let epoll_mgr = EpollManager::default();
-            let mut dev: Net<Arc<GuestMemoryMmap>, QueueSync, GuestRegionMmap> = Net::new(
-                String::from("test_vhosttap"),
-                Some(&guest_mac),
-                queue_sizes,
-                epoll_mgr,
-            )
-            .unwrap();
-
+            let tap_name = unique_tap_name("vtap");
+            let dev_result: VirtioResult<Net<Arc<GuestMemoryMmap>, QueueSync, GuestRegionMmap>> =
+                Net::new(tap_name.clone(), Some(&guest_mac), queue_sizes, epoll_mgr);
+            let mut dev: Net<Arc<GuestMemoryMmap>, QueueSync, GuestRegionMmap> = match dev_result {
+                Ok(d) => d,
+                Err(e) => {
+                    eprintln!("skip test: failed to create tap {}: {:?}", tap_name, e);
+                    return;
+                }
+            };
             let queues = vec![
                 VirtioQueueConfig::create(128, 0).unwrap(),
                 VirtioQueueConfig::create(128, 0).unwrap(),
@@ -809,13 +823,17 @@ mod tests {
             let queue_eventfd2 = Arc::new(EventFd::new(0).unwrap());
             let queue_sizes = Arc::new(vec![128, 128]);
             let epoll_mgr = EpollManager::default();
-            let mut dev: Net<Arc<GuestMemoryMmap>, Queue, GuestRegionMmap> = Net::new(
-                String::from("test_vhosttap"),
-                Some(&guest_mac),
-                queue_sizes,
-                epoll_mgr,
-            )
-            .unwrap();
+
+            let tap_name = unique_tap_name("vtap");
+            let dev_result: VirtioResult<Net<Arc<GuestMemoryMmap>, Queue, GuestRegionMmap>> =
+                Net::new(tap_name.clone(), Some(&guest_mac), queue_sizes, epoll_mgr);
+            let mut dev: Net<Arc<GuestMemoryMmap>, Queue, GuestRegionMmap> = match dev_result {
+                Ok(d) => d,
+                Err(e) => {
+                    eprintln!("skip test: failed to create tap {}: {:?}", tap_name, e);
+                    return;
+                }
+            };
 
             let queues = vec![
                 VirtioQueueConfig::new(queue, queue_eventfd, notifier.clone(), 1),