unittest: net: eliminate ReadTapMock::MockFrame

The test code has two ways to inject a packet to be read from the tap
device: Using the `TapTrafficSimulator`, which actually uses `sendto` to
send something through the tap device, or `MockFrame`, which hijacks
`Net::read_tap` to not actually read from the tap and just return the
packet. Eliminate the latter, as it was only used in a single test, and
needless complicates the test setup (well, arguably, unittests shouldn't
use actual Tap devices, and thus we should eliminte
`TapTrafficSimulator` instead, but I'm choosing my battles today).

Do the injection of the packet before we deplete the ratelimiter, as
otherwise the injection takes long enough for the ratelimiter to
replenish, causing the test to fail intermittently. Also increase the
replenish time.

Signed-off-by: Patrick Roy <[email protected]>

src/vmm/src/devices/virtio/net/device.rs

@@ -964,10 +964,6 @@ pub mod tests {
     impl Net {
         pub(crate) fn read_tap(&mut self) -> io::Result<usize> {
             match &self.tap.mocks.read_tap {
-                ReadTapMock::MockFrame(frame) => {
-                    self.rx_frame_buf[..frame.len()].copy_from_slice(frame);
-                    Ok(frame.len())
-                }
                 ReadTapMock::Failure => Err(io::Error::new(
                     io::ErrorKind::Other,
                     "Read tap synthetically failed.",
@@ -1911,18 +1907,22 @@ pub mod tests {
 
         // Test RX bandwidth rate limiting
         {
-            // create bandwidth rate limiter that allows 40960 bytes/s with bucket size 4096 bytes
-            let mut rl = RateLimiter::new(0x1000, 0, 100, 0, 0, 0).unwrap();
-            // use up the budget
-            assert!(rl.consume(0x1000, TokenType::Bytes));
-
-            // set this rx rate limiter to be used
-            th.net().rx_rate_limiter = rl;
+            // create bandwidth rate limiter that allows 2000 bytes/s with bucket size 1000 bytes
+            let mut rl = RateLimiter::new(1000, 0, 500, 0, 0, 0).unwrap();
 
             // set up RX
             assert!(!th.net().rx_deferred_frame);
             th.add_desc_chain(NetQueue::Rx, 0, &[(0, 4096, VIRTQ_DESC_F_WRITE)]);
 
+            let frame = inject_tap_tx_frame(&th.net(), 1000);
+
+            // use up the budget (do it after injecting the tx frame, as socket communication is
+            // slow enough that the ratelimiter could replenish in the meantime).
+            assert!(rl.consume(1000, TokenType::Bytes));
+
+            // set this rx rate limiter to be used
+            th.net().rx_rate_limiter = rl;
+
             // following RX procedure should fail because of bandwidth rate limiting
             {
                 // trigger the RX handler
@@ -1946,13 +1946,12 @@ pub mod tests {
                 assert_eq!(th.net().metrics.rx_rate_limiter_throttled.count(), 2);
             }
 
-            // wait for 100ms to give the rate-limiter timer a chance to replenish
-            // wait for an extra 100ms to make sure the timerfd event makes its way from the kernel
-            thread::sleep(Duration::from_millis(200));
+            // wait for 500ms to give the rate-limiter timer a chance to replenish
+            // wait for an extra 500ms to make sure the timerfd event makes its way from the kernel
+            thread::sleep(Duration::from_millis(1000));
 
             // following RX procedure should succeed because bandwidth should now be available
             {
-                let frame = &th.net().tap.mocks.read_tap.mock_frame();
                 // no longer throttled
                 check_metric_after_block!(
                     th.net().metrics.rx_rate_limiter_throttled,
@@ -1967,7 +1966,7 @@ pub mod tests {
                 assert_eq!(th.rxq.used.idx.get(), 1);
                 th.rxq
                     .check_used_elem(0, 0, frame.len().try_into().unwrap());
-                th.rxq.dtable[0].check_data(frame);
+                th.rxq.dtable[0].check_data(&frame);
             }
         }
     }
@@ -2025,18 +2024,20 @@ pub mod tests {
 
         // Test RX ops rate limiting
         {
-            // create ops rate limiter that allows 10 ops/s with bucket size 1 ops
-            let mut rl = RateLimiter::new(0, 0, 0, 1, 0, 100).unwrap();
+            // create ops rate limiter that allows 2 ops/s with bucket size 1 ops
+            let mut rl = RateLimiter::new(0, 0, 0, 1, 0, 500).unwrap();
+
+            // set up RX
+            assert!(!th.net().rx_deferred_frame);
+            th.add_desc_chain(NetQueue::Rx, 0, &[(0, 4096, VIRTQ_DESC_F_WRITE)]);
+            let frame = inject_tap_tx_frame(&th.net(), 1234);
+
             // use up the initial budget
             assert!(rl.consume(1, TokenType::Ops));
 
             // set this rx rate limiter to be used
             th.net().rx_rate_limiter = rl;
 
-            // set up RX
-            assert!(!th.net().rx_deferred_frame);
-            th.add_desc_chain(NetQueue::Rx, 0, &[(0, 4096, VIRTQ_DESC_F_WRITE)]);
-
             // following RX procedure should fail because of ops rate limiting
             {
                 // trigger the RX handler
@@ -2063,21 +2064,20 @@ pub mod tests {
                 assert_eq!(th.rxq.used.idx.get(), 0);
             }
 
-            // wait for 100ms to give the rate-limiter timer a chance to replenish
-            // wait for an extra 100ms to make sure the timerfd event makes its way from the kernel
-            thread::sleep(Duration::from_millis(200));
+            // wait for 500ms to give the rate-limiter timer a chance to replenish
+            // wait for an extra 500ms to make sure the timerfd event makes its way from the kernel
+            thread::sleep(Duration::from_millis(1000));
 
             // following RX procedure should succeed because ops should now be available
             {
-                let frame = &th.net().tap.mocks.read_tap.mock_frame();
                 th.simulate_event(NetEvent::RxRateLimiter);
                 // make sure the virtio queue operation completed this time
                 assert!(&th.net().irq_trigger.has_pending_irq(IrqType::Vring));
                 // make sure the data queue advanced
                 assert_eq!(th.rxq.used.idx.get(), 1);
                 th.rxq
                     .check_used_elem(0, 0, frame.len().try_into().unwrap());
-                th.rxq.dtable[0].check_data(frame);
+                th.rxq.dtable[0].check_data(&frame);
             }
         }
     }

src/vmm/src/devices/virtio/net/test_utils.rs

@@ -6,7 +6,6 @@
 use std::fs::File;
 use std::mem;
 use std::os::raw::c_ulong;
-use std::os::unix::ffi::OsStrExt;
 use std::os::unix::io::{AsRawFd, FromRawFd};
 use std::process::Command;
 use std::str::FromStr;
@@ -80,19 +79,9 @@ pub fn default_net_no_mmds() -> Net {
 #[derive(Debug)]
 pub enum ReadTapMock {
     Failure,
-    MockFrame(Vec<u8>),
     TapFrame,
 }
 
-impl ReadTapMock {
-    pub fn mock_frame(&self) -> Vec<u8> {
-        if let ReadTapMock::MockFrame(frame) = self {
-            return frame.clone();
-        }
-        panic!("Can't get last mock frame");
-    }
-}
-
 #[derive(Debug)]
 pub enum WriteTapMock {
     Failure,
@@ -119,9 +108,7 @@ impl Mocks {
 impl Default for Mocks {
     fn default() -> Mocks {
         Mocks {
-            read_tap: ReadTapMock::MockFrame(
-                utils::rand::rand_alphanumerics(1234).as_bytes().to_vec(),
-            ),
+            read_tap: ReadTapMock::TapFrame,
             write_tap: WriteTapMock::Success,
         }
     }
@@ -298,6 +285,8 @@ pub fn enable(tap: &Tap) {
 
 #[cfg(test)]
 pub(crate) fn inject_tap_tx_frame(net: &Net, len: usize) -> Vec<u8> {
+    use std::os::unix::ffi::OsStrExt;
+
     assert!(len >= vnet_hdr_len());
     let tap_traffic_simulator = TapTrafficSimulator::new(if_index(&net.tap));
     let mut frame = utils::rand::rand_alphanumerics(len - vnet_hdr_len())