virtio: make add_buf return capacity remaining

This API change means that virtio_net can tell how much capacity
remains for buffers.  It's necessarily fuzzy, since
VIRTIO_RING_F_INDIRECT_DESC means we can fit any number of descriptors
in one, *if* we can kmalloc.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Cc: Dinesh Subhraveti <dineshs@us.ibm.com>

8 files changed, 19 insertions, 15 deletions

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index aa1a3d5a3e2..d739ee4201f 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -139,7 +139,7 @@ static bool do_req(struct request_queue *q, struct virtio_blk *vblk,
                 }
         }
 
-        if (vblk->vq->vq_ops->add_buf(vblk->vq, vblk->sg, out, in, vbr)) {
+        if (vblk->vq->vq_ops->add_buf(vblk->vq, vblk->sg, out, in, vbr) < 0) {
                 mempool_free(vbr, vblk->pool);
                 return false;
         }
diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c
index 32216b62324..b6c24dcc987 100644
--- a/drivers/char/hw_random/virtio-rng.c
+++ b/drivers/char/hw_random/virtio-rng.c
@@ -51,7 +51,7 @@ static void register_buffer(void)
 
         sg_init_one(&sg, random_data+data_left, RANDOM_DATA_SIZE-data_left);
         /* There should always be room for one buffer. */
-        if (vq->vq_ops->add_buf(vq, &sg, 0, 1, random_data) != 0)
+        if (vq->vq_ops->add_buf(vq, &sg, 0, 1, random_data) < 0)
                 BUG();
         vq->vq_ops->kick(vq);
 }
diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index c74dacfa679..a035ae39a35 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -65,7 +65,7 @@ static int put_chars(u32 vtermno, const char *buf, int count)
 
         /* add_buf wants a token to identify this buffer: we hand it any
          * non-NULL pointer, since there's only ever one buffer. */
-        if (out_vq->vq_ops->add_buf(out_vq, sg, 1, 0, (void *)1) == 0) {
+        if (out_vq->vq_ops->add_buf(out_vq, sg, 1, 0, (void *)1) >= 0) {
                 /* Tell Host to go! */
                 out_vq->vq_ops->kick(out_vq);
                 /* Chill out until it's done with the buffer. */
@@ -85,7 +85,7 @@ static void add_inbuf(void)
         sg_init_one(sg, inbuf, PAGE_SIZE);
 
         /* We should always be able to add one buffer to an empty queue. */
-        if (in_vq->vq_ops->add_buf(in_vq, sg, 0, 1, inbuf) != 0)
+        if (in_vq->vq_ops->add_buf(in_vq, sg, 0, 1, inbuf) < 0)
                 BUG();
         in_vq->vq_ops->kick(in_vq);
 }
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 32266fb89c2..fbf04a553f5 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -320,7 +320,7 @@ static bool try_fill_recv_maxbufs(struct virtnet_info *vi, gfp_t gfp)
                 skb_queue_head(&vi->recv, skb);
 
                 err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, num, skb);
-                if (err) {
+                if (err < 0) {
                         skb_unlink(skb, &vi->recv);
                         trim_pages(vi, skb);
                         kfree_skb(skb);
@@ -373,7 +373,7 @@ static bool try_fill_recv(struct virtnet_info *vi, gfp_t gfp)
                 skb_queue_head(&vi->recv, skb);
 
                 err = vi->rvq->vq_ops->add_buf(vi->rvq, sg, 0, 1, skb);
-                if (err) {
+                if (err < 0) {
                         skb_unlink(skb, &vi->recv);
                         kfree_skb(skb);
                         break;
@@ -527,7 +527,7 @@ static int xmit_skb(struct virtnet_info *vi, struct sk_buff *skb)
         num = skb_to_sgvec(skb, sg+1, 0, skb->len) + 1;
 
         err = vi->svq->vq_ops->add_buf(vi->svq, sg, num, 0, skb);
-        if (!err && !vi->free_in_tasklet)
+        if (err >= 0 && !vi->free_in_tasklet)
                 mod_timer(&vi->xmit_free_timer, jiffies + (HZ/10));
 
         return err;
@@ -538,7 +538,7 @@ static void xmit_tasklet(unsigned long data)
         struct virtnet_info *vi = (void *)data;
 
         netif_tx_lock_bh(vi->dev);
-        if (vi->last_xmit_skb && xmit_skb(vi, vi->last_xmit_skb) == 0) {
+        if (vi->last_xmit_skb && xmit_skb(vi, vi->last_xmit_skb) >= 0) {
                 vi->svq->vq_ops->kick(vi->svq);
                 vi->last_xmit_skb = NULL;
         }
@@ -557,7 +557,7 @@ again:
 
         /* If we has a buffer left over from last time, send it now. */
         if (unlikely(vi->last_xmit_skb) &&
-            xmit_skb(vi, vi->last_xmit_skb) != 0)
+            xmit_skb(vi, vi->last_xmit_skb) < 0)
                 goto stop_queue;
 
         vi->last_xmit_skb = NULL;
@@ -565,7 +565,7 @@ again:
         /* Put new one in send queue and do transmit */
         if (likely(skb)) {
                 __skb_queue_head(&vi->send, skb);
-                if (xmit_skb(vi, skb) != 0) {
+                if (xmit_skb(vi, skb) < 0) {
                         vi->last_xmit_skb = skb;
                         skb = NULL;
                         goto stop_queue;
@@ -668,7 +668,7 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
                 sg_set_buf(&sg[i + 1], sg_virt(s), s->length);
         sg_set_buf(&sg[out + in - 1], &status, sizeof(status));
 
-        BUG_ON(vi->cvq->vq_ops->add_buf(vi->cvq, sg, out, in, vi));
+        BUG_ON(vi->cvq->vq_ops->add_buf(vi->cvq, sg, out, in, vi) < 0);
 
         vi->cvq->vq_ops->kick(vi->cvq);
 
diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
index 26b27826479..39789232646 100644
--- a/drivers/virtio/virtio_balloon.c
+++ b/drivers/virtio/virtio_balloon.c
@@ -84,7 +84,7 @@ static void tell_host(struct virtio_balloon *vb, struct virtqueue *vq)
         init_completion(&vb->acked);
 
         /* We should always be able to add one buffer to an empty queue. */
-        if (vq->vq_ops->add_buf(vq, &sg, 1, 0, vb) != 0)
+        if (vq->vq_ops->add_buf(vq, &sg, 1, 0, vb) < 0)
                 BUG();
         vq->vq_ops->kick(vq);
 
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index a882f260651..f5360058072 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -208,7 +208,11 @@ add_head:
 
         pr_debug("Added buffer head %i to %p\n", head, vq);
         END_USE(vq);
-        return 0;
+
+        /* If we're indirect, we can fit many (assuming not OOM). */
+        if (vq->indirect)
+                return vq->num_free ? vq->vring.num : 0;
+        return vq->num_free;
 }
 
 static void vring_kick(struct virtqueue *_vq)
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 4fca4f5440b..057a2e01075 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -34,7 +34,7 @@ struct virtqueue {
  *      out_num: the number of sg readable by other side
  *      in_num: the number of sg which are writable (after readable ones)
  *      data: the token identifying the buffer.
- *      Returns 0 or an error.
+ *      Returns remaining capacity of queue (sg segments) or a negative error.
  * @kick: update after add_buf
  *      vq: the struct virtqueue
  *      After one or more add_buf calls, invoke this to kick the other side.
diff --git a/net/9p/trans_virtio.c b/net/9p/trans_virtio.c
index 9bf0b737aa5..53c139d31a2 100644
--- a/net/9p/trans_virtio.c
+++ b/net/9p/trans_virtio.c
@@ -200,7 +200,7 @@ p9_virtio_request(struct p9_client *client, struct p9_req_t *req)
 
         req->status = REQ_STATUS_SENT;
 
-        if (chan->vq->vq_ops->add_buf(chan->vq, chan->sg, out, in, req->tc)) {
+        if (chan->vq->vq_ops->add_buf(chan->vq, chan->sg, out, in, req->tc) < 0) {
                 P9_DPRINTK(P9_DEBUG_TRANS,
                         "9p debug: virtio rpc add_buf returned failure");
                 return -EIO;