On 09/18/2017 11:15 AM, Ben Pfaff wrote:
On Mon, Sep 18, 2017 at 10:58:28AM -0700, Greg Rose wrote:
On 09/12/2017 08:37 PM, ychen wrote:
in function nla_alloc_flow_actions(), there is a check if action length is
greater than MAX_ACTIONS_BUFSIZE(32k), then kernel datapath flow will not be
installed, and packets will droppped.
but in function xlate_actions(), there is such clause:
if (nl_attr_oversized(ctx.odp_actions->size)) {
/* These datapath actions are too big for a Netlink attribute, so we
* can't hand them to the kernel directly. dpif_execute() can execute
* them one by one with help, so just mark the result as SLOW_ACTION to
* prevent the flow from being installed. */
COVERAGE_INC(xlate_actions_oversize);
ctx.xout->slow |= SLOW_ACTION;
}
and in function nl_attr_oversized(), the clause is like this:
return payload_size > UINT16_MAX - NLA_HDRLEN;
so we can see that in user space, max action length is almost 64K, but in
kernel space, max action length is only 32K.
my question is: why the max action length is different? packet will drop when
its action length exceeds 32K, but packet can excute in slow path when its
action length exceeds 64K?
It's a kernel limitation.
http://www.spinics.net/lists/netdev/msg431592.html
It sounds like the userspace limit, then, should also be 32 kB (or
possibly 16 kB). I guess we should fix that.
Correct, the user space limit should be 32KB. That's what it is in iproute2.
Thanks,
- Greg
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