On Tue, 2012-06-12 at 16:33 +0200, Eric Dumazet wrote: 

On Tue, 2012-06-12 at 16:03 +0200, Eric Dumazet wrote:

quoted

On Tue, 2012-06-12 at 15:48 +0200, Rostislav Lisovy wrote:

quoted

em_canid is an ematch capable of classifying CAN frames according to
their CAN IDs.

This RFC/Patch contains a reworked classifier initially posted in
http://www.spinics.net/lists/netdev/msg200114.html
The functionality is the same however there is almost 50% reduction
in the source code length.

There is a slight difference between this ematch and other available
ematches. Other ematches implement only a simple match operation and
are meant to be combined with logic conjunctions (e.g. AND, OR).
Our ematch makes it possible to use up to 32 rules in single
'configuration statement' (with OR semantics). This allows us to take
the advantage of the bit field data-structure in the implementation of
the match function.

Example: canid(sff 0x123 eff 0x124 sff 0x230:0x7f0)
This ematch would match CAN SFF frames with the following IDs:
0x123, 0x230--0x23f or EFF frame with ID 0x124.

Signed-off-by: Rostislav Lisovy <redacted>
---
 include/linux/can.h     |    3 +
 include/linux/pkt_cls.h |    5 +-
 net/sched/Kconfig       |   10 +++
 net/sched/Makefile      |    1 +
 net/sched/em_canid.c    |  217 +++++++++++++++++++++++++++++++++++++++++++++++
 5 files changed, 234 insertions(+), 2 deletions(-)
 create mode 100644 net/sched/em_canid.c

diff --git a/include/linux/can.h b/include/linux/can.h
index 9a19bcb..08d1610 100644
--- a/include/linux/can.h
+++ b/include/linux/can.h

@@ -38,6 +38,9 @@
  */
 typedef __u32 canid_t;
 
+#define CAN_SFF_ID_BITS		11
+#define CAN_EFF_ID_BITS		29
+

quoted

+struct canid_match {
+	struct can_filter rules_raw[EM_CAN_RULES_SIZE]; /* Raw rules copied
+		from netlink message; Used for sending information to
+		userspace (when 'tc filter show' is invoked) AND when
+		matching EFF frames*/
+	DECLARE_BITMAP(match_sff, (1 << CAN_SFF_ID_BITS)); /* For each SFF CAN
+		ID (11 bit) there is one record in this	bitfield */
+	int rules_count;
+	int eff_rules_count;
+	int sff_rules_count;
+
+	struct rcu_head rcu;
+};

The size of kmalloc() blob to hold this structure is 4 Mbytes

This is a huge cost, and unlikely to succeed but shortly after boot...

(this happens to be the largest possible kmalloc() allocation by the way
on x86)

Oh well, I mixed CAN_SFF_ID_BITS / CAN_EFF_ID_BITS

Indeed; On x86_64 the sizeof(struct canid_match) is 544 bytes;

Regards;
Rostislav Lisovy