xen/netfront: disentangle tx_skb_freelist

The tx_skb_freelist elements are in a single linked list with the
request id used as link reference. The per element link field is in a
union with the skb pointer of an in use request.

Move the link reference out of the union in order to enable a later
reuse of it for requests which need a populated skb pointer.

Rename add_id_to_freelist() and get_id_from_freelist() to
add_id_to_list() and get_id_from_list() in order to prepare using
those for other lists as well. Define ~0 as value to indicate the end
of a list and place that value into the link for a request not being
on the list.

When freeing a skb zero the skb pointer in the request. Use a NULL
value of the skb pointer instead of skb_entry_is_link() for deciding
whether a request has a skb linked to it.

Remove skb_entry_set_link() and open code it instead as it is really
trivial now.

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/xen-netfront.c b/drivers/net/xen-netfront.c
index 714fe9d..956e126 100644 (file)
--- a/drivers/net/xen-netfront.c
+++ b/drivers/net/xen-netfront.c
@@ -126,17 +126,11 @@ struct netfront_queue {
 
        /*
         * {tx,rx}_skbs store outstanding skbuffs. Free tx_skb entries
-        * are linked from tx_skb_freelist through skb_entry.link.
-        *
-        *  NB. Freelist index entries are always going to be less than
-        *  PAGE_OFFSET, whereas pointers to skbs will always be equal or
-        *  greater than PAGE_OFFSET: we use this property to distinguish
-        *  them.
+        * are linked from tx_skb_freelist through tx_link.
         */
-       union skb_entry {
-               struct sk_buff *skb;
-               unsigned long link;
-       } tx_skbs[NET_TX_RING_SIZE];
+       struct sk_buff *tx_skbs[NET_TX_RING_SIZE];
+       unsigned short tx_link[NET_TX_RING_SIZE];
+#define TX_LINK_NONE 0xffff
        grant_ref_t gref_tx_head;
        grant_ref_t grant_tx_ref[NET_TX_RING_SIZE];
        struct page *grant_tx_page[NET_TX_RING_SIZE];
@@ -181,33 +175,25 @@ struct netfront_rx_info {
        struct xen_netif_extra_info extras[XEN_NETIF_EXTRA_TYPE_MAX - 1];
 };
 
-static void skb_entry_set_link(union skb_entry *list, unsigned short id)
-{
-       list->link = id;
-}
-
-static int skb_entry_is_link(const union skb_entry *list)
-{
-       BUILD_BUG_ON(sizeof(list->skb) != sizeof(list->link));
-       return (unsigned long)list->skb < PAGE_OFFSET;
-}
-
 /*
  * Access macros for acquiring freeing slots in tx_skbs[].
  */
 
-static void add_id_to_freelist(unsigned *head, union skb_entry *list,
-                              unsigned short id)
+static void add_id_to_list(unsigned *head, unsigned short *list,
+                          unsigned short id)
 {
-       skb_entry_set_link(&list[id], *head);
+       list[id] = *head;
        *head = id;
 }
 
-static unsigned short get_id_from_freelist(unsigned *head,
-                                          union skb_entry *list)
+static unsigned short get_id_from_list(unsigned *head, unsigned short *list)
 {
        unsigned int id = *head;
-       *head = list[id].link;
+
+       if (id != TX_LINK_NONE) {
+               *head = list[id];
+               list[id] = TX_LINK_NONE;
+       }
        return id;
 }
 
@@ -406,7 +392,8 @@ static void xennet_tx_buf_gc(struct netfront_queue *queue)
                                continue;
 
                        id  = txrsp.id;
-                       skb = queue->tx_skbs[id].skb;
+                       skb = queue->tx_skbs[id];
+                       queue->tx_skbs[id] = NULL;
                        if (unlikely(gnttab_query_foreign_access(
                                queue->grant_tx_ref[id]) != 0)) {
                                pr_alert("%s: warning -- grant still in use by backend domain\n",
@@ -419,7 +406,7 @@ static void xennet_tx_buf_gc(struct netfront_queue *queue)
                                &queue->gref_tx_head, queue->grant_tx_ref[id]);
                        queue->grant_tx_ref[id] = GRANT_INVALID_REF;
                        queue->grant_tx_page[id] = NULL;
-                       add_id_to_freelist(&queue->tx_skb_freelist, queue->tx_skbs, id);
+                       add_id_to_list(&queue->tx_skb_freelist, queue->tx_link, id);
                        dev_kfree_skb_irq(skb);
                }
 
@@ -452,7 +439,7 @@ static void xennet_tx_setup_grant(unsigned long gfn, unsigned int offset,
        struct netfront_queue *queue = info->queue;
        struct sk_buff *skb = info->skb;
 
-       id = get_id_from_freelist(&queue->tx_skb_freelist, queue->tx_skbs);
+       id = get_id_from_list(&queue->tx_skb_freelist, queue->tx_link);
        tx = RING_GET_REQUEST(&queue->tx, queue->tx.req_prod_pvt++);
        ref = gnttab_claim_grant_reference(&queue->gref_tx_head);
        WARN_ON_ONCE(IS_ERR_VALUE((unsigned long)(int)ref));
@@ -460,7 +447,7 @@ static void xennet_tx_setup_grant(unsigned long gfn, unsigned int offset,
        gnttab_grant_foreign_access_ref(ref, queue->info->xbdev->otherend_id,
                                        gfn, GNTMAP_readonly);
 
-       queue->tx_skbs[id].skb = skb;
+       queue->tx_skbs[id] = skb;
        queue->grant_tx_page[id] = page;
        queue->grant_tx_ref[id] = ref;
 
@@ -1284,17 +1271,18 @@ static void xennet_release_tx_bufs(struct netfront_queue *queue)
 
        for (i = 0; i < NET_TX_RING_SIZE; i++) {
                /* Skip over entries which are actually freelist references */
-               if (skb_entry_is_link(&queue->tx_skbs[i]))
+               if (!queue->tx_skbs[i])
                        continue;
 
-               skb = queue->tx_skbs[i].skb;
+               skb = queue->tx_skbs[i];
+               queue->tx_skbs[i] = NULL;
                get_page(queue->grant_tx_page[i]);
                gnttab_end_foreign_access(queue->grant_tx_ref[i],
                                          GNTMAP_readonly,
                                          (unsigned long)page_address(queue->grant_tx_page[i]));
                queue->grant_tx_page[i] = NULL;
                queue->grant_tx_ref[i] = GRANT_INVALID_REF;
-               add_id_to_freelist(&queue->tx_skb_freelist, queue->tx_skbs, i);
+               add_id_to_list(&queue->tx_skb_freelist, queue->tx_link, i);
                dev_kfree_skb_irq(skb);
        }
 }
@@ -1851,13 +1839,14 @@ static int xennet_init_queue(struct netfront_queue *queue)
        snprintf(queue->name, sizeof(queue->name), "vif%s-q%u",
                 devid, queue->id);
 
-       /* Initialise tx_skbs as a free chain containing every entry. */
+       /* Initialise tx_skb_freelist as a free chain containing every entry. */
        queue->tx_skb_freelist = 0;
        for (i = 0; i < NET_TX_RING_SIZE; i++) {
-               skb_entry_set_link(&queue->tx_skbs[i], i+1);
+               queue->tx_link[i] = i + 1;
                queue->grant_tx_ref[i] = GRANT_INVALID_REF;
                queue->grant_tx_page[i] = NULL;
        }
+       queue->tx_link[NET_TX_RING_SIZE - 1] = TX_LINK_NONE;
 
        /* Clear out rx_skbs */
        for (i = 0; i < NET_RX_RING_SIZE; i++) {