v2.3: xdp: fix draining at exit when zerocopy is enabled (backport of #7284) (#7293)

xdp: fix draining at exit when zerocopy is enabled (#7284)

Starting from 219f805 we always add
some umem frames to the fill ring to avoid driver bugs. Since we don't
actually use the RX path, those frames are never filled and returned to
the umem, therefore shouldn't wait for them when we drain on exit.

(cherry picked from commit 77450a5)

Co-authored-by: Alessandro Decina <[email protected]>

Author: mergify[bot]

xdp/src/tx_loop.rs

@@ -77,6 +77,7 @@ pub fn tx_loop<T: AsRef<[u8]>>(
     };
 
     let umem = socket.umem();
+    let umem_tx_capacity = umem.available();
     let Tx {
         // this is where we'll queue frames
         ring,
@@ -271,11 +272,11 @@ pub fn tx_loop<T: AsRef<[u8]>>(
     assert_eq!(batched_packets, 0);
 
     // drain the ring
-    while umem.available() < umem.capacity() || ring.available() < ring.capacity() {
+    while umem.available() < umem_tx_capacity || ring.available() < ring.capacity() {
         log::debug!(
             "draining xdp ring umem {}/{} ring {}/{}",
             umem.available(),
-            umem.capacity(),
+            umem_tx_capacity,
             ring.available(),
             ring.capacity()
         );