[Qemu-devel] [RFC/ PATCH 4/4] virtio-9p: convert lstat to use async infrastructure.

[Gautham R Shenoy <ego@in.ibm.com>]

This patch converts v9fs_stat() to make use of the async infrastructure.

Every call to v9fs_stat() is processed in the context of the vcpu thread before
offloading the actual stat operation onto an async-thread. The post operation is
handled in the context of the io-thread which in turn does the complete()
operation for this particular v9fs_stat() operation.

Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
---
 hw/virtio-9p.c |   34 ++++++++++++++++++++++------------
 hw/virtio-9p.h |    4 ++++
 2 files changed, 26 insertions(+), 12 deletions(-)

diff --git a/hw/virtio-9p.c b/hw/virtio-9p.c
index f8f60d3..a57fffc 100644
--- a/hw/virtio-9p.c
+++ b/hw/virtio-9p.c
@@ -1218,26 +1218,38 @@ out:
     v9fs_string_free(&aname);
 }
 
-static void v9fs_stat_post_lstat(V9fsState *s, V9fsStatState *vs, int err)
+static void v9fs_stat_post_lstat(void *opaque)
 {
-    if (err == -1) {
-        err = -errno;
+    V9fsStatState *vs = (V9fsStatState *)opaque;
+
+    if (vs->err == -1) {
+        vs->err = -(vs->v9fs_errno);
         goto out;
     }
 
-    err = stat_to_v9stat(s, &vs->fidp->path, &vs->stbuf, &vs->v9stat);
-    if (err) {
+    vs->err = stat_to_v9stat(vs->s, &vs->fidp->path, &vs->stbuf, &vs->v9stat);
+    if (vs->err) {
         goto out;
     }
     vs->offset += pdu_marshal(vs->pdu, vs->offset, "wS", 0, &vs->v9stat);
-    err = vs->offset;
+    vs->err = vs->offset;
 
 out:
-    complete_pdu(s, vs->pdu, err);
+    complete_pdu(vs->s, vs->pdu, vs->err);
     v9fs_stat_free(&vs->v9stat);
     qemu_free(vs);
 }
 
+static void v9fs_stat_do_lstat(struct work_item *work)
+{
+    V9fsStatState *vs = (V9fsStatState *)work->private;
+
+    vs->err = v9fs_do_lstat(vs->s, &vs->fidp->path, &vs->stbuf);
+    vs->v9fs_errno = errno;
+
+    v9fs_async_signal(vs->post_fn, vs);
+}
+
 static void v9fs_stat(V9fsState *s, V9fsPDU *pdu)
 {
     int32_t fid;
@@ -1247,6 +1259,7 @@ static void v9fs_stat(V9fsState *s, V9fsPDU *pdu)
     vs = qemu_malloc(sizeof(*vs));
     vs->pdu = pdu;
     vs->offset = 7;
+    vs->s = s;
 
     memset(&vs->v9stat, 0, sizeof(vs->v9stat));
 
@@ -1258,8 +1271,8 @@ static void v9fs_stat(V9fsState *s, V9fsPDU *pdu)
         goto out;
     }
 
-    err = v9fs_do_lstat(s, &vs->fidp->path, &vs->stbuf);
-    v9fs_stat_post_lstat(s, vs, err);
+    v9fs_do_async_posix(vs, v9fs_stat_do_lstat, &vs->post_fn,
+                        v9fs_stat_post_lstat);
     return;
 
 out:
@@ -2559,8 +2572,5 @@ VirtIODevice *virtio_9p_init(DeviceState *dev, V9fsConf *conf)
     /* Create async queue. */
     async_queue_init(&v9fs_async_struct.virtio_9p_aqueue, 10, 3);
 
-    (void)v9fs_do_async_posix;
-    (void)v9fs_async_signal;
-
     return &s->vdev;
 }
diff --git a/hw/virtio-9p.h b/hw/virtio-9p.h
index 992c765..b4a1d46 100644
--- a/hw/virtio-9p.h
+++ b/hw/virtio-9p.h
@@ -173,6 +173,10 @@ typedef struct V9fsStatState {
     V9fsStat v9stat;
     V9fsFidState *fidp;
     struct stat stbuf;
+    V9fsState *s;
+    int err;
+    int v9fs_errno;
+    void (*post_fn)(void *arg);
 } V9fsStatState;
 
 typedef struct V9fsWalkState {