[PATCH net v2 1/4] net/core: relax BUILD_BUG_ON in netdev_stats_to_stats64

From: Jarod Wilson
Date: Thu Jan 28 2016 - 10:50:19 EST


The netdev_stats_to_stats64 function copies the deprecated
net_device_stats format stats into rtnl_link_stats64 for legacy support
purposes, but with the BUILD_BUG_ON as it was, it wasn't possible to
extend rtnl_link_stats64 without also extending net_device_stats. Relax
the BUILD_BUG_ON to only require that rtnl_link_stats64 is larger, and
zero out all the stat counters that aren't present in net_device_stats.

CC: Eric Dumazet <edumazet@xxxxxxxxxx>
Signed-off-by: Jarod Wilson <jarod@xxxxxxxxxx>
---
net/core/dev.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 8cba3d8..575a7df 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -7253,25 +7253,30 @@ void netdev_run_todo(void)
}
}

-/* Convert net_device_stats to rtnl_link_stats64. They have the same
- * fields in the same order, with only the type differing.
+/* Convert net_device_stats to rtnl_link_stats64. rtnl_link_stats64 has
+ * all the same fields in the same order as net_device_stats, with only
+ * the type differing, but rtnl_link_stats64 may have additional fields
+ * at the end for newer counters.
*/
void netdev_stats_to_stats64(struct rtnl_link_stats64 *stats64,
const struct net_device_stats *netdev_stats)
{
#if BITS_PER_LONG == 64
- BUILD_BUG_ON(sizeof(*stats64) != sizeof(*netdev_stats));
+ BUILD_BUG_ON(sizeof(*stats64) < sizeof(*netdev_stats));
memcpy(stats64, netdev_stats, sizeof(*stats64));
#else
size_t i, n = sizeof(*stats64) / sizeof(u64);
const unsigned long *src = (const unsigned long *)netdev_stats;
u64 *dst = (u64 *)stats64;

- BUILD_BUG_ON(sizeof(*netdev_stats) / sizeof(unsigned long) !=
+ BUILD_BUG_ON(sizeof(*netdev_stats) / sizeof(unsigned long) >
sizeof(*stats64) / sizeof(u64));
for (i = 0; i < n; i++)
dst[i] = src[i];
#endif
+ /* zero out counters that only exist in rtnl_link_stats64 */
+ memset((char *)stats64 + sizeof(*netdev_stats), 0,
+ sizeof(*stats64) - sizeof(*netdev_stats));
}
EXPORT_SYMBOL(netdev_stats_to_stats64);

--
1.8.3.1