xen-netback: better names for thresholds

This patch only changes some names to avoid confusion.

In this patch we have:

  MAX_SKB_SLOTS_DEFAULT -> FATAL_SKB_SLOTS_DEFAULT
  max_skb_slots -> fatal_skb_slots
  #define XEN_NETBK_LEGACY_SLOTS_MAX XEN_NETIF_NR_SLOTS_MIN

The fatal_skb_slots is the threshold to determine whether a packet is
malicious.

XEN_NETBK_LEGACY_SLOTS_MAX is the maximum slots a valid packet can have at
this point. It is defined to be XEN_NETIF_NR_SLOTS_MIN because that's
guaranteed to be supported by all backends.

Suggested-by: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 29 insertions, 20 deletions

diff --git a/drivers/net/xen-netback/netback.c b/drivers/net/xen-netback/netback.c
index ce8109f7d56f..37984e6d4e99 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -51,9 +51,17 @@
  * This is the maximum slots a skb can have. If a guest sends a skb
  * which exceeds this limit it is considered malicious.
  */
-#define MAX_SKB_SLOTS_DEFAULT 20
-static unsigned int max_skb_slots = MAX_SKB_SLOTS_DEFAULT;
-module_param(max_skb_slots, uint, 0444);
+#define FATAL_SKB_SLOTS_DEFAULT 20
+static unsigned int fatal_skb_slots = FATAL_SKB_SLOTS_DEFAULT;
+module_param(fatal_skb_slots, uint, 0444);
+
+/*
+ * To avoid confusion, we define XEN_NETBK_LEGACY_SLOTS_MAX indicating
+ * the maximum slots a valid packet can use. Now this value is defined
+ * to be XEN_NETIF_NR_SLOTS_MIN, which is supposed to be supported by
+ * all backend.
+ */
+#define XEN_NETBK_LEGACY_SLOTS_MAX XEN_NETIF_NR_SLOTS_MIN
 
 typedef unsigned int pending_ring_idx_t;
 #define INVALID_PENDING_RING_IDX (~0U)
@@ -953,25 +961,26 @@ static int netbk_count_requests(struct xenvif *vif,
                 /* This guest is really using too many slots and
                  * considered malicious.
                  */
-                if (unlikely(slots >= max_skb_slots)) {
+                if (unlikely(slots >= fatal_skb_slots)) {
                         netdev_err(vif->dev,
                                    "Malicious frontend using %d slots, threshold %u\n",
-                                   slots, max_skb_slots);
+                                   slots, fatal_skb_slots);
                         netbk_fatal_tx_err(vif);
                         return -E2BIG;
                 }
 
                 /* Xen network protocol had implicit dependency on
-                 * MAX_SKB_FRAGS. XEN_NETIF_NR_SLOTS_MIN is set to the
-                 * historical MAX_SKB_FRAGS value 18 to honor the same
-                 * behavior as before. Any packet using more than 18
-                 * slots but less than max_skb_slots slots is dropped
+                 * MAX_SKB_FRAGS. XEN_NETBK_LEGACY_SLOTS_MAX is set to
+                 * the historical MAX_SKB_FRAGS value 18 to honor the
+                 * same behavior as before. Any packet using more than
+                 * 18 slots but less than fatal_skb_slots slots is
+                 * dropped
                  */
-                if (!drop_err && slots >= XEN_NETIF_NR_SLOTS_MIN) {
+                if (!drop_err && slots >= XEN_NETBK_LEGACY_SLOTS_MAX) {
                         if (net_ratelimit())
                                 netdev_dbg(vif->dev,
                                            "Too many slots (%d) exceeding limit (%d), dropping packet\n",
-                                           slots, XEN_NETIF_NR_SLOTS_MIN);
+                                           slots, XEN_NETBK_LEGACY_SLOTS_MAX);
                         drop_err = -E2BIG;
                 }
 
@@ -1053,7 +1062,7 @@ static struct gnttab_copy *xen_netbk_get_requests(struct xen_netbk *netbk,
         struct pending_tx_info *first = NULL;
 
         /* At this point shinfo->nr_frags is in fact the number of
-         * slots, which can be as large as XEN_NETIF_NR_SLOTS_MIN.
+         * slots, which can be as large as XEN_NETBK_LEGACY_SLOTS_MAX.
          */
         nr_slots = shinfo->nr_frags;
 
@@ -1415,12 +1424,12 @@ static unsigned xen_netbk_tx_build_gops(struct xen_netbk *netbk)
         struct sk_buff *skb;
         int ret;
 
-        while ((nr_pending_reqs(netbk) + XEN_NETIF_NR_SLOTS_MIN
+        while ((nr_pending_reqs(netbk) + XEN_NETBK_LEGACY_SLOTS_MAX
                 < MAX_PENDING_REQS) &&
                 !list_empty(&netbk->net_schedule_list)) {
                 struct xenvif *vif;
                 struct xen_netif_tx_request txreq;
-                struct xen_netif_tx_request txfrags[XEN_NETIF_NR_SLOTS_MIN];
+                struct xen_netif_tx_request txfrags[XEN_NETBK_LEGACY_SLOTS_MAX];
                 struct page *page;
                 struct xen_netif_extra_info extras[XEN_NETIF_EXTRA_TYPE_MAX-1];
                 u16 pending_idx;
@@ -1508,7 +1517,7 @@ static unsigned xen_netbk_tx_build_gops(struct xen_netbk *netbk)
                 pending_idx = netbk->pending_ring[index];
 
                 data_len = (txreq.size > PKT_PROT_LEN &&
-                            ret < XEN_NETIF_NR_SLOTS_MIN) ?
+                            ret < XEN_NETBK_LEGACY_SLOTS_MAX) ?
                         PKT_PROT_LEN : txreq.size;
 
                 skb = alloc_skb(data_len + NET_SKB_PAD + NET_IP_ALIGN,
@@ -1787,7 +1796,7 @@ static inline int rx_work_todo(struct xen_netbk *netbk)
 static inline int tx_work_todo(struct xen_netbk *netbk)
 {
 
-        if ((nr_pending_reqs(netbk) + XEN_NETIF_NR_SLOTS_MIN
+        if ((nr_pending_reqs(netbk) + XEN_NETBK_LEGACY_SLOTS_MAX
              < MAX_PENDING_REQS) &&
              !list_empty(&netbk->net_schedule_list))
                 return 1;
@@ -1872,11 +1881,11 @@ static int __init netback_init(void)
         if (!xen_domain())
                 return -ENODEV;
 
-        if (max_skb_slots < XEN_NETIF_NR_SLOTS_MIN) {
+        if (fatal_skb_slots < XEN_NETBK_LEGACY_SLOTS_MAX) {
                 printk(KERN_INFO
-                       "xen-netback: max_skb_slots too small (%d), bump it to XEN_NETIF_NR_SLOTS_MIN (%d)\n",
-                       max_skb_slots, XEN_NETIF_NR_SLOTS_MIN);
-                max_skb_slots = XEN_NETIF_NR_SLOTS_MIN;
+                       "xen-netback: fatal_skb_slots too small (%d), bump it to XEN_NETBK_LEGACY_SLOTS_MAX (%d)\n",
+                       fatal_skb_slots, XEN_NETBK_LEGACY_SLOTS_MAX);
+                fatal_skb_slots = XEN_NETBK_LEGACY_SLOTS_MAX;
         }
 
         xen_netbk_group_nr = num_online_cpus();