[Xen-devel] [PATCH net-next v7 1/9] xen-netback: Use skb->cb for pending_idx

[Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>]

Storing the pending_idx at the first byte of the linear buffer never looked
good, skb->cb is a more proper place for this. It also prevents the header to
be directly grant copied there, and we don't have the pending_idx after we
copied the header here, so it's time to change it.
It also introduces helpers for the RX side

Signed-off-by: Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>
---
v7:
- using helpers to access skb->cb, on RX side too

diff --git a/drivers/net/xen-netback/netback.c 
b/drivers/net/xen-netback/netback.c
index e5284bc..43ae4ba 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -455,10 +455,12 @@ static void xenvif_add_frag_responses(struct xenvif *vif, 
int status,
        }
 }
 
-struct skb_cb_overlay {
+struct xenvif_rx_cb {
        int meta_slots_used;
 };
 
+#define XENVIF_RX_CB(skb) ((struct xenvif_rx_cb *)(skb)->cb)
+
 void xenvif_kick_thread(struct xenvif *vif)
 {
        wake_up(&vif->wq);
@@ -474,7 +476,6 @@ static void xenvif_rx_action(struct xenvif *vif)
        LIST_HEAD(notify);
        int ret;
        unsigned long offset;
-       struct skb_cb_overlay *sco;
        bool need_to_notify = false;
 
        struct netrx_pending_operations npo = {
@@ -513,9 +514,8 @@ static void xenvif_rx_action(struct xenvif *vif)
                } else
                        vif->rx_last_skb_slots = 0;
 
-               sco = (struct skb_cb_overlay *)skb->cb;
-               sco->meta_slots_used = xenvif_gop_skb(skb, &npo);
-               BUG_ON(sco->meta_slots_used > max_slots_needed);
+               XENVIF_RX_CB(skb)->meta_slots_used = xenvif_gop_skb(skb, &npo);
+               BUG_ON(XENVIF_RX_CB(skb)->meta_slots_used > max_slots_needed);
 
                __skb_queue_tail(&rxq, skb);
        }
@@ -529,7 +529,6 @@ static void xenvif_rx_action(struct xenvif *vif)
        gnttab_batch_copy(vif->grant_copy_op, npo.copy_prod);
 
        while ((skb = __skb_dequeue(&rxq)) != NULL) {
-               sco = (struct skb_cb_overlay *)skb->cb;
 
                if ((1 << vif->meta[npo.meta_cons].gso_type) &
                    vif->gso_prefix_mask) {
@@ -540,19 +539,21 @@ static void xenvif_rx_action(struct xenvif *vif)
 
                        resp->offset = vif->meta[npo.meta_cons].gso_size;
                        resp->id = vif->meta[npo.meta_cons].id;
-                       resp->status = sco->meta_slots_used;
+                       resp->status = XENVIF_RX_CB(skb)->meta_slots_used;
 
                        npo.meta_cons++;
-                       sco->meta_slots_used--;
+                       XENVIF_RX_CB(skb)->meta_slots_used--;
                }
 
 
                vif->dev->stats.tx_bytes += skb->len;
                vif->dev->stats.tx_packets++;
 
-               status = xenvif_check_gop(vif, sco->meta_slots_used, &npo);
+               status = xenvif_check_gop(vif,
+                                         XENVIF_RX_CB(skb)->meta_slots_used,
+                                         &npo);
 
-               if (sco->meta_slots_used == 1)
+               if (XENVIF_RX_CB(skb)->meta_slots_used == 1)
                        flags = 0;
                else
                        flags = XEN_NETRXF_more_data;
@@ -589,13 +590,13 @@ static void xenvif_rx_action(struct xenvif *vif)
 
                xenvif_add_frag_responses(vif, status,
                                          vif->meta + npo.meta_cons + 1,
-                                         sco->meta_slots_used);
+                                         XENVIF_RX_CB(skb)->meta_slots_used);
 
                RING_PUSH_RESPONSES_AND_CHECK_NOTIFY(&vif->rx, ret);
 
                need_to_notify |= !!ret;
 
-               npo.meta_cons += sco->meta_slots_used;
+               npo.meta_cons += XENVIF_RX_CB(skb)->meta_slots_used;
                dev_kfree_skb(skb);
        }
 
@@ -772,6 +773,13 @@ static struct page *xenvif_alloc_page(struct xenvif *vif,
        return page;
 }
 
+
+struct xenvif_tx_cb {
+       u16 pending_idx;
+};
+
+#define XENVIF_TX_CB(skb) ((struct xenvif_tx_cb *)(skb)->cb)
+
 static struct gnttab_copy *xenvif_get_requests(struct xenvif *vif,
                                               struct sk_buff *skb,
                                               struct xen_netif_tx_request *txp,
@@ -779,7 +787,7 @@ static struct gnttab_copy *xenvif_get_requests(struct 
xenvif *vif,
 {
        struct skb_shared_info *shinfo = skb_shinfo(skb);
        skb_frag_t *frags = shinfo->frags;
-       u16 pending_idx = *((u16 *)skb->data);
+       u16 pending_idx = XENVIF_TX_CB(skb)->pending_idx;
        u16 head_idx = 0;
        int slot, start;
        struct page *page;
@@ -897,7 +905,7 @@ static int xenvif_tx_check_gop(struct xenvif *vif,
                               struct gnttab_copy **gopp)
 {
        struct gnttab_copy *gop = *gopp;
-       u16 pending_idx = *((u16 *)skb->data);
+       u16 pending_idx = XENVIF_TX_CB(skb)->pending_idx;
        struct skb_shared_info *shinfo = skb_shinfo(skb);
        struct pending_tx_info *tx_info;
        int nr_frags = shinfo->nr_frags;
@@ -944,7 +952,7 @@ static int xenvif_tx_check_gop(struct xenvif *vif,
                        continue;
 
                /* First error: invalidate header and preceding fragments. */
-               pending_idx = *((u16 *)skb->data);
+               pending_idx = XENVIF_TX_CB(skb)->pending_idx;
                xenvif_idx_release(vif, pending_idx, XEN_NETIF_RSP_OKAY);
                for (j = start; j < i; j++) {
                        pending_idx = frag_get_pending_idx(&shinfo->frags[j]);
@@ -1236,7 +1244,7 @@ static unsigned xenvif_tx_build_gops(struct xenvif *vif, 
int budget)
                memcpy(&vif->pending_tx_info[pending_idx].req,
                       &txreq, sizeof(txreq));
                vif->pending_tx_info[pending_idx].head = index;
-               *((u16 *)skb->data) = pending_idx;
+               XENVIF_TX_CB(skb)->pending_idx = pending_idx;
 
                __skb_put(skb, data_len);
 
@@ -1283,7 +1291,7 @@ static int xenvif_tx_submit(struct xenvif *vif)
                u16 pending_idx;
                unsigned data_len;
 
-               pending_idx = *((u16 *)skb->data);
+               pending_idx = XENVIF_TX_CB(skb)->pending_idx;
                txp = &vif->pending_tx_info[pending_idx].req;
 
                /* Check the remap error code. */

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