1 files changed, 41 insertions, 0 deletions

diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
index 281c1bded1f6..51b968d3febb 100644
--- a/net/sched/sch_api.c
+++ b/net/sched/sch_api.c
@@ -285,6 +285,45 @@ static struct Qdisc_ops *qdisc_lookup_ops(struct nlattr *kind)
         return q;
 }
 
+/* The linklayer setting were not transferred from iproute2, in older
+ * versions, and the rate tables lookup systems have been dropped in
+ * the kernel. To keep backward compatible with older iproute2 tc
+ * utils, we detect the linklayer setting by detecting if the rate
+ * table were modified.
+ *
+ * For linklayer ATM table entries, the rate table will be aligned to
+ * 48 bytes, thus some table entries will contain the same value.  The
+ * mpu (min packet unit) is also encoded into the old rate table, thus
+ * starting from the mpu, we find low and high table entries for
+ * mapping this cell.  If these entries contain the same value, when
+ * the rate tables have been modified for linklayer ATM.
+ *
+ * This is done by rounding mpu to the nearest 48 bytes cell/entry,
+ * and then roundup to the next cell, calc the table entry one below,
+ * and compare.
+ */
+static __u8 __detect_linklayer(struct tc_ratespec *r, __u32 *rtab)
+{
+        int low       = roundup(r->mpu, 48);
+        int high      = roundup(low+1, 48);
+        int cell_low  = low >> r->cell_log;
+        int cell_high = (high >> r->cell_log) - 1;
+
+        /* rtab is too inaccurate at rates > 100Mbit/s */
+        if ((r->rate > (100000000/8)) || (rtab[0] == 0)) {
+                pr_debug("TC linklayer: Giving up ATM detection\n");
+                return TC_LINKLAYER_ETHERNET;
+        }
+
+        if ((cell_high > cell_low) && (cell_high < 256)
+            && (rtab[cell_low] == rtab[cell_high])) {
+                pr_debug("TC linklayer: Detected ATM, low(%d)=high(%d)=%u\n",
+                         cell_low, cell_high, rtab[cell_high]);
+                return TC_LINKLAYER_ATM;
+        }
+        return TC_LINKLAYER_ETHERNET;
+}
+
 static struct qdisc_rate_table *qdisc_rtab_list;
 
 struct qdisc_rate_table *qdisc_get_rtab(struct tc_ratespec *r, struct nlattr *tab)
@@ -308,6 +347,8 @@ struct qdisc_rate_table *qdisc_get_rtab(struct tc_ratespec *r, struct nlattr *ta
                 rtab->rate = *r;
                 rtab->refcnt = 1;
                 memcpy(rtab->data, nla_data(tab), 1024);
+                if (r->linklayer == TC_LINKLAYER_UNAWARE)
+                        r->linklayer = __detect_linklayer(r, rtab->data);
                 rtab->next = qdisc_rtab_list;
                 qdisc_rtab_list = rtab;
         }