From: Roopa Prabhu <ro...@cumulusnetworks.com>
Date: Mon, 18 Apr 2016 14:10:19 -0700
> This patch adds a new RTM_GETSTATS message to query link stats via
> netlink from the kernel. RTM_NEWLINK also dumps stats today, but
> RTM_NEWLINK returns a lot more than just stats and is expensive in
> some cases when frequent polling for stats from userspace is a
> common operation.
I'm holding off on this until we sort out the 64-bit netlink
attribute alignment issue.
Meanwhile, I'll some kind of a fix into the tree for the
rtnl_fill_stats() change so that it doesn't cause unaligned
accesses.
I just tested out a clever idea, where for architectures where
unaligned accesses is a problem, we insert a zero length NOP attribute
before the 64-bit stats. This makes it properly aligned. A quick
hack patch just passed testing on my sparc64 box, but I'll go over it
some more.
diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
index bb3a90b..5ffdcb3 100644
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -155,6 +155,7 @@ enum {
IFLA_PROTO_DOWN,
IFLA_GSO_MAX_SEGS,
IFLA_GSO_MAX_SIZE,
+ IFLA_PAD,
__IFLA_MAX
};
diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
index a7a3d34..b192576 100644
--- a/net/core/rtnetlink.c
+++ b/net/core/rtnetlink.c
@@ -1052,6 +1052,15 @@ static noinline_for_stack int rtnl_fill_stats(struct
sk_buff *skb,
struct rtnl_link_stats64 *sp;
struct nlattr *attr;
+ /* Add a zero length NOP attribute so that the nla_data()
+ * of the IFLA_STATS64 will be 64-bit aligned.
+ */
+#ifndef HAVE_EFFICIENT_UNALIGNED_ACCESS
+ attr = nla_reserve(skb, IFLA_PAD, 0);
+ if (!attr)
+ return -EMSGSIZE;
+#endif
+
attr = nla_reserve(skb, IFLA_STATS64,
sizeof(struct rtnl_link_stats64));
if (!attr)
