[Qemu-devel] [PATCH 1/2] libvhost-user: support resuming vq->last_avail_idx based on used_idx

[Marc-André Lureau]

This is the same workaround as commit 523b018dde3b765, which was lost
with libvhost-user transition in commit e10e798c85c2331.

Signed-off-by: Marc-André Lureau <address@hidden>
---
 contrib/libvhost-user/libvhost-user.h |  5 +++++
 contrib/libvhost-user/libvhost-user.c | 13 +++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/contrib/libvhost-user/libvhost-user.h 
b/contrib/libvhost-user/libvhost-user.h
index 53ef222c0b..aca71717c1 100644
--- a/contrib/libvhost-user/libvhost-user.h
+++ b/contrib/libvhost-user/libvhost-user.h
@@ -132,6 +132,7 @@ typedef void (*vu_set_features_cb) (VuDev *dev, uint64_t 
features);
 typedef int (*vu_process_msg_cb) (VuDev *dev, VhostUserMsg *vmsg,
                                   int *do_reply);
 typedef void (*vu_queue_set_started_cb) (VuDev *dev, int qidx, bool started);
+typedef bool (*vu_queue_resume_to_used_cb) (VuDev *dev, int qidx);
 
 typedef struct VuDevIface {
     /* called by VHOST_USER_GET_FEATURES to get the features bitmask */
@@ -148,6 +149,10 @@ typedef struct VuDevIface {
     vu_process_msg_cb process_msg;
     /* tells when queues can be processed */
     vu_queue_set_started_cb queue_set_started;
+    /* If the queue must be resumed to vring.used->idx. */
+    /* This can help to support resuming on unmanaged exit/crash when
+     * the slave/driver processes elements in order. */
+    vu_queue_resume_to_used_cb queue_resume_to_used;
 } VuDevIface;
 
 typedef void (*vu_queue_handler_cb) (VuDev *dev, int qidx);
diff --git a/contrib/libvhost-user/libvhost-user.c 
b/contrib/libvhost-user/libvhost-user.c
index 35fa0c5e56..36439caed6 100644
--- a/contrib/libvhost-user/libvhost-user.c
+++ b/contrib/libvhost-user/libvhost-user.c
@@ -521,6 +521,19 @@ vu_set_vring_addr_exec(VuDev *dev, VhostUserMsg *vmsg)
 
     vq->used_idx = vq->vring.used->idx;
 
+    if (vq->last_avail_idx != vq->used_idx) {
+        bool resume = dev->iface->queue_resume_to_used &&
+            dev->iface->queue_resume_to_used(dev, index);
+
+        DPRINT("Last avail index != used index: %u != %u%s\n",
+               vq->last_avail_idx, vq->used_idx,
+               resume ? ", resuming" : "");
+
+        if (resume) {
+            vq->shadow_avail_idx = vq->last_avail_idx = vq->used_idx;
+        }
+    }
+
     return false;
 }
 
-- 
2.14.1.146.gd35faa819