Re: [PATCH] tests/qtest/libqos: Avoid double swapping when using modern virtio

[Philippe Mathieu-Daudé]

On 30/4/25 09:33, Thomas Huth wrote:
From: Thomas Huth <th...@redhat.com>
The logic in the qvirtio_read/write function is rather a headache,
involving byte-swapping when the target is big endian, just to
maybe involve another byte-swapping  in the qtest_read/write
function immediately afterwards (on the QEMU side). Let's do it in
a more obvious way here: For virtio 1.0, we know that the values have
to be little endian, so let's read/write the bytes in that well known
order here.

Thanks for looking at this!


Signed-off-by: Thomas Huth <th...@redhat.com>
---
  This also decreases our usage of qtest_big_endian() which might (or
  might not) get helpful for the universal binary one day...

  tests/qtest/libqos/virtio.c | 61 ++++++++++++++++++++++++++-----------
  1 file changed, 44 insertions(+), 17 deletions(-)

diff --git a/tests/qtest/libqos/virtio.c b/tests/qtest/libqos/virtio.c
index 2e7979652fd..078adf3c8dc 100644
--- a/tests/qtest/libqos/virtio.c
+++ b/tests/qtest/libqos/virtio.c
@@ -25,49 +25,76 @@
   */
  static uint16_t qvirtio_readw(QVirtioDevice *d, QTestState *qts, uint64_t 
addr)
  {
-    uint16_t val = qtest_readw(qts, addr);
+    uint8_t buf[2];
  
-    if (d->features & (1ull << VIRTIO_F_VERSION_1) && qtest_big_endian(qts)) {
-        val = bswap16(val);
+    if (d->features & (1ull << VIRTIO_F_VERSION_1)) {
+        qtest_memread(qts, addr, buf, sizeof(buf));
+        return (buf[1] << 8) | buf[0];
+    } else {
+        return qtest_readw(qts, addr);
      }
-    return val;
  }

What about using cpu_to_le() API?

-- >8 --
 static uint16_t qvirtio_readw(QVirtioDevice *d, QTestState *qts, 
uint64_t addr)
 {
-    uint16_t val = qtest_readw(qts, addr);
+    uint16_t val;

-    if (d->features & (1ull << VIRTIO_F_VERSION_1) && 
qtest_big_endian(qts)) {
-        val = bswap16(val);
+    if (d->features & (1ull << VIRTIO_F_VERSION_1)) {
+        qtest_memread(qts, addr, &val, sizeof(val));
+        cpu_to_le16s(&val);
+    } else {
+        val = qtest_readw(qts, addr);
     }
+
     return val;
 }
---