tests/qtest/libqos: add qvirtqueue_reset_pool() for descriptor pool reset

Add a function to reset the virtqueue descriptor pool state without
reinitializing the device. This is useful for tests that issue a high
number of requests and are limited by the simplified virtio test
driver's descriptor tracking, which decrements num_free but never
increments it back.

The function is safe for synchronous test code where requests are
sent and completed before the next request is issued.

Acked-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/qemu-devel/96cf23eea1204b34443218fe76bd4a5eaf9163e8.1779126034.git.qemu_oss@crudebyte.com
Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
(cherry picked from commit be33c56898f8b18617cff91525f0b68abee8de07)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

2 files changed, 25 insertions, 0 deletions

diff --git a/tests/qtest/libqos/virtio.c b/tests/qtest/libqos/virtio.c
index 2e7979652f..dfa94700cb 100644
--- a/tests/qtest/libqos/virtio.c
+++ b/tests/qtest/libqos/virtio.c
@@ -442,6 +442,29 @@ bool qvirtqueue_get_buf(QTestState *qts, QVirtQueue *vq, uint32_t *desc_idx,
     return true;
 }
 
+/*
+ * qvirtqueue_reset_pool:
+ * @vq: The virtqueue to reset
+ *
+ * Reset the descriptor pool state without reinitializing the device.
+ * This is useful for tests that issue a high number of requests and
+ * are limited by the simplified virtio test driver's descriptor tracking,
+ * which decrements num_free but never increments it back.
+ *
+ * This is only safe for synchronous test code where requests are
+ * sent and completed before the next request is issued. Do not use
+ * with asynchronous code where multiple requests may be in-flight.
+ *
+ * Note: This only resets the available descriptor pool (free_head,
+ * num_free). The used ring position (last_used_idx) is NOT reset
+ * and should continue to track consumed responses across iterations.
+ */
+void qvirtqueue_reset_pool(QVirtQueue *vq)
+{
+    vq->free_head = 0;
+    vq->num_free = vq->size;
+}
+
 void qvirtqueue_set_used_event(QTestState *qts, QVirtQueue *vq, uint16_t idx)
 {
     g_assert(vq->event);
diff --git a/tests/qtest/libqos/virtio.h b/tests/qtest/libqos/virtio.h
index 7adc7cbd10..d6486ba7f9 100644
--- a/tests/qtest/libqos/virtio.h
+++ b/tests/qtest/libqos/virtio.h
@@ -148,6 +148,8 @@ void qvirtqueue_kick(QTestState *qts, QVirtioDevice *d, QVirtQueue *vq,
 bool qvirtqueue_get_buf(QTestState *qts, QVirtQueue *vq, uint32_t *desc_idx,
                         uint32_t *len);
 
+void qvirtqueue_reset_pool(QVirtQueue *vq);
+
 void qvirtqueue_set_used_event(QTestState *qts, QVirtQueue *vq, uint16_t idx);
 
 void qvirtio_start_device(QVirtioDevice *vdev);