virtio-devices: vhost-user: Use TimerFd connect_vhost_user

Replace the use of sleeps with a TimerFd. Initially this is functionally
equivalent but it can be extended to also handle other events.

Signed-off-by: Rob Bradford <rbradford@meta.com>

virtio-devices/src/seccomp_filters.rs

@@ -198,6 +198,8 @@ fn virtio_vhost_fs_thread_rules() -> Vec<(i64, Vec<SeccompRule>)> {
         (libc::SYS_sendmsg, vec![]),
         (libc::SYS_sendto, vec![]),
         (libc::SYS_socket, vec![]),
+        (libc::SYS_timerfd_create, vec![]),
+        (libc::SYS_timerfd_settime, vec![]),
     ]
 }
 
@@ -212,6 +214,8 @@ fn virtio_generic_vhost_user_thread_rules() -> Vec<(i64, Vec<SeccompRule>)> {
         (libc::SYS_sendmsg, vec![]),
         (libc::SYS_sendto, vec![]),
         (libc::SYS_socket, vec![]),
+        (libc::SYS_timerfd_create, vec![]),
+        (libc::SYS_timerfd_settime, vec![]),
     ]
 }
 
@@ -232,6 +236,8 @@ fn virtio_vhost_net_thread_rules() -> Vec<(i64, Vec<SeccompRule>)> {
         (libc::SYS_sendmsg, vec![]),
         (libc::SYS_sendto, vec![]),
         (libc::SYS_socket, vec![]),
+        (libc::SYS_timerfd_create, vec![]),
+        (libc::SYS_timerfd_settime, vec![]),
         #[cfg(target_arch = "x86_64")]
         (libc::SYS_unlink, vec![]),
         #[cfg(target_arch = "aarch64")]
@@ -247,6 +253,8 @@ fn virtio_vhost_block_thread_rules() -> Vec<(i64, Vec<SeccompRule>)> {
         (libc::SYS_recvmsg, vec![]),
         (libc::SYS_sendmsg, vec![]),
         (libc::SYS_socket, vec![]),
+        (libc::SYS_timerfd_create, vec![]),
+        (libc::SYS_timerfd_settime, vec![]),
     ]
 }
 

virtio-devices/src/vhost_user/mod.rs

@@ -72,7 +72,7 @@ pub enum Error {
     #[error("Failed to open vhost device")]
     VhostUserOpen(#[source] VhostError),
     #[error("Connection to socket failed")]
-    VhostUserConnect,
+    VhostUserConnect(#[source] VhostError),
     #[error("Get features failed")]
     VhostUserGetFeatures(#[source] VhostError),
     #[error("Get queue max number failed")]
@@ -159,6 +159,18 @@ pub enum Error {
     VringBasesCountMismatch(usize, usize),
     #[error("Backend state and vring bases must both be present or both be absent")]
     InconsistentBackendState,
+    #[error("Failed to create timerfd")]
+    TimerFdCreate(#[source] io::Error),
+    #[error("Failed to arm timerfd")]
+    TimerFdArm(#[source] io::Error),
+    #[error("Failed waiting on timerfd")]
+    TimerFdWait(#[source] io::Error),
+    #[error("Failed to create epoll instance")]
+    EpollCreate(#[source] io::Error),
+    #[error("Failed to add fd to epoll")]
+    EpollCtl(#[source] io::Error),
+    #[error("Failed waiting on epoll")]
+    EpollWait(#[source] io::Error),
 }
 type Result<T> = std::result::Result<T, Error>;
 

virtio-devices/src/vhost_user/vu_common_ctrl.rs

@@ -8,7 +8,6 @@ use std::os::unix::io::{AsRawFd, FromRawFd, OwnedFd, RawFd};
 use std::os::unix::net::{UnixListener, UnixStream};
 use std::sync::Arc;
 use std::sync::atomic::Ordering;
-use std::thread::sleep;
 use std::time::{Duration, Instant};
 
 use log::{error, info};
@@ -26,7 +25,9 @@ use virtio_queue::{Queue, QueueT};
 use vm_memory::guest_memory::Error as MmapError;
 use vm_memory::{Address, FileOffset, GuestAddress, GuestMemory, GuestMemoryRegion};
 use vm_migration::protocol::MemoryRangeTable;
+use vmm_sys_util::epoll::{ControlOperation, Epoll, EpollEvent, EventSet};
 use vmm_sys_util::eventfd::EventFd;
+use vmm_sys_util::timerfd::TimerFd;
 
 use super::{Error, Result, VhostUserState};
 use crate::vhost_user::Inflight;
@@ -402,10 +403,28 @@ impl VhostUserHandle {
                 queue_indexes: Vec::new(),
             })
         } else {
-            let now = Instant::now();
+            const RETRY_INTERVAL: Duration = Duration::from_millis(100);
+            const CONNECT_TIMEOUT: Duration = Duration::from_secs(60);
+            const TIMER_EVENT: u64 = 0;
 
-            // Retry connecting for a full minute
-            let err = loop {
+            let mut retry_timer = TimerFd::new().map_err(|e| Error::TimerFdCreate(e.into()))?;
+            retry_timer
+                .reset(RETRY_INTERVAL, Some(RETRY_INTERVAL))
+                .map_err(|e| Error::TimerFdArm(e.into()))?;
+
+            let epoll = Epoll::new().map_err(Error::EpollCreate)?;
+            epoll
+                .ctl(
+                    ControlOperation::Add,
+                    retry_timer.as_raw_fd(),
+                    EpollEvent::new(EventSet::IN, TIMER_EVENT),
+                )
+                .map_err(Error::EpollCtl)?;
+
+            let start = Instant::now();
+            let mut events = [EpollEvent::default(); 1];
+
+            loop {
                 let err = match Frontend::connect(socket_path, num_queues) {
                     Ok(m) => {
                         return Ok(VhostUserHandle {
@@ -421,17 +440,27 @@ impl VhostUserHandle {
                     }
                     Err(e) => e,
                 };
-                sleep(Duration::from_millis(100));
 
-                if now.elapsed().as_secs() >= 60 {
-                    break err;
+                if start.elapsed() >= CONNECT_TIMEOUT {
+                    error!(
+                        "Failed connecting the backend after trying for 1 minute for socket {socket_path}: {err:?}"
+                    );
+                    return Err(Error::VhostUserConnect(err));
                 }
-            };
 
-            error!(
-                "Failed connecting the backend after trying for 1 minute for socket {socket_path}: {err:?}"
-            );
-            Err(Error::VhostUserConnect)
+                loop {
+                    match epoll.wait(-1, &mut events) {
+                        Ok(_) => break,
+                        Err(e) if e.kind() == std::io::ErrorKind::Interrupted => continue,
+                        Err(e) => return Err(Error::EpollWait(e)),
+                    }
+                }
+
+                // Drain the timerfd so it stops signaling.
+                retry_timer
+                    .wait()
+                    .map_err(|e| Error::TimerFdWait(e.into()))?;
+            }
         }
     }