[PATCH RFC 04/13] vhost: cleanup fetch_buf return code handling

[Michael S. Tsirkin]

Return code of fetch_buf is confusing, so callers resort to
tricks to get to sane values. Let's switch to something standard:
0 empty, >0 non-empty, <0 error.

Signed-off-by: Michael S. Tsirkin <m...@redhat.com>
---
 drivers/vhost/vhost.c | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index aca2a5b0d078..bd52b44b0d23 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -2146,6 +2146,8 @@ static int fetch_indirect_descs(struct vhost_virtqueue 
*vq,
        return 0;
 }
 
+/* This function returns a value > 0 if a descriptor was found, or 0 if none 
were found.
+ * A negative code is returned on error. */
 static int fetch_buf(struct vhost_virtqueue *vq)
 {
        unsigned int i, head, found = 0;
@@ -2162,7 +2164,7 @@ static int fetch_buf(struct vhost_virtqueue *vq)
        if (unlikely(vq->avail_idx == vq->last_avail_idx)) {
                /* If we already have work to do, don't bother re-checking. */
                if (likely(vq->ndescs))
-                       return vq->num;
+                       return 0;
 
                if (unlikely(vhost_get_avail_idx(vq, &avail_idx))) {
                        vq_err(vq, "Failed to access avail idx at %p\n",
@@ -2181,7 +2183,7 @@ static int fetch_buf(struct vhost_virtqueue *vq)
                 * invalid.
                 */
                if (vq->avail_idx == last_avail_idx)
-                       return vq->num;
+                       return 0;
 
                /* Only get avail ring entries after they have been
                 * exposed by guest.
@@ -2251,12 +2253,14 @@ static int fetch_buf(struct vhost_virtqueue *vq)
        /* On success, increment avail index. */
        vq->last_avail_idx++;
 
-       return 0;
+       return 1;
 }
 
+/* This function returns a value > 0 if a descriptor was found, or 0 if none 
were found.
+ * A negative code is returned on error. */
 static int fetch_descs(struct vhost_virtqueue *vq)
 {
-       int ret = 0;
+       int ret;
 
        if (unlikely(vq->first_desc >= vq->ndescs)) {
                vq->first_desc = 0;
@@ -2266,10 +2270,14 @@ static int fetch_descs(struct vhost_virtqueue *vq)
        if (vq->ndescs)
                return 0;
 
-       while (!ret && vq->ndescs <= vhost_vq_num_batch_descs(vq))
-               ret = fetch_buf(vq);
+       for (ret = 1;
+            ret > 0 && vq->ndescs <= vhost_vq_num_batch_descs(vq);
+            ret = fetch_buf(vq))
+               ;
 
-       return vq->ndescs ? 0 : ret;
+       /* On success we expect some descs */
+       BUG_ON(ret > 0 && !vq->ndescs);
+       return ret;
 }
 
 /* This looks in the virtqueue and for the first available buffer, and converts
@@ -2288,7 +2296,7 @@ int vhost_get_vq_desc(struct vhost_virtqueue *vq,
        int ret = fetch_descs(vq);
        int i;
 
-       if (ret)
+       if (ret <= 0)
                return ret;
 
        /* Now convert to IOV */
-- 
MST