On Wed, 10 May 2017 11:36:22 +0200, Daniel Borkmann wrote:
> On 05/10/2017 05:18 AM, Jakub Kicinski wrote:
> > On Wed, 10 May 2017 03:31:31 +0200, Daniel Borkmann wrote:
> >> @@ -6851,6 +6851,32 @@ int dev_change_proto_down(struct net_device *dev,
> >> bool proto_down)
> >> }
> >> EXPORT_SYMBOL(dev_change_proto_down);
> >>
> >> +bool __dev_xdp_attached(struct net_device *dev, xdp_op_t xdp_op)
> >
> > Out of curiosity - the leading underscores refer to caller having to
> > hold rtnl? I assume they are not needed in the function below because
> > it's static?
>
> I think I don't quite follow the last question, but it probably makes
> sense to add an ASSERT_RTNL() into dev_xdp_attached() inline helper to
> make it clearly visible to callers of this api.
Sorry, I missed you have a dev_xdp_attached() defined in the header,
hence the confusion.
> >> +{
> >> + struct netdev_xdp xdp;
> >> +
> >> + memset(&xdp, 0, sizeof(xdp));
> >> + xdp.command = XDP_QUERY_PROG;
> >
> > Probably personal preference, but seems like designated struct
> > initializer would do quite nicely here and save the memset :)
>
> I had that initially, but I recalled that gcc < 4.6 does not handle this
> style for the initialization of anonymous struct/union properly (e.g.,
> we fixed that in iproute2 as well). Andrew Morton still uses gcc 4.4.4
> and occasionally sends kernel fixes, so we might end up like this anyway.
Ah, good to know!
> >> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> >> index dda9f16..99320f0 100644
> >> --- a/net/core/rtnetlink.c
> >> +++ b/net/core/rtnetlink.c
> >> @@ -1251,24 +1251,20 @@ static int rtnl_xdp_fill(struct sk_buff *skb,
> >> struct net_device *dev)
> >> {
> >> struct nlattr *xdp;
> >> u32 xdp_flags = 0;
> >> - u8 val = 0;
> >> int err;
> >> + u8 val;
> >>
> >> xdp = nla_nest_start(skb, IFLA_XDP);
> >> if (!xdp)
> >> return -EMSGSIZE;
> >> +
> >> if (rcu_access_pointer(dev->xdp_prog)) {
> >> xdp_flags = XDP_FLAGS_SKB_MODE;
> >> val = 1;
> >> - } else if (dev->netdev_ops->ndo_xdp) {
> >> - struct netdev_xdp xdp_op = {};
> >> -
> >> - xdp_op.command = XDP_QUERY_PROG;
> >> - err = dev->netdev_ops->ndo_xdp(dev, &xdp_op);
> >> - if (err)
> >> - goto err_cancel;
> >> - val = xdp_op.prog_attached;
> >> + } else {
> >> + val = dev_xdp_attached(dev);
> >> }
> >
> > Would it make sense to set xdp_flags to XDP_FLAGS_DRV_MODE here to keep
> > things symmetrical? I know you are just preserving existing behaviour
> > but it may seem slightly arbitrary to a new comer to report one of the
> > very similarly named flags in the dump but not the other.
>
> I thought about it, it's kind of redundant information since
> IFLA_XDP_ATTACHED attribute w/o IFLA_XDP_FLAGS attribute today
> says that it's native already. It might look strange if we add
> also XDP_FLAGS_DRV_MODE there, since it doesn't give anything
> new. I rather see it similar to XDP_FLAGS_UPDATE_IF_NOEXIST flag
> that is for updating fd only, but I don't really have a strong
> opinion on this though. I could add it to the respin if preferred.
XDP_FLAGS_UPDATE_IF_NOEXIST is indeed the precedent which makes things
a bit murky. There are no reasonably useful semantics for IF_NOEXIST
on dump :( Note that meaning of SKB_MODE flag shifts slightly between
set and dump IIUC. At set time it means:
"force installation at the generic hook",
at dump time it means:
"installed at generic hook - regardless of whether the flag was set at
installation time",
So I would argue that DRV_MODE flag is closer to SKB_MODE not only by
name but also by semantics, and it would be cool if we could keep the
semantics close on dump as well as set.
I understand the counter argument that from user space perspective it
would make things slightly more complicated because there would be two
conditions in which driver hook is used:
1) DRV_MODE set on dump;
2) flags attribute not present (old kernel).
I'm concerned about number 2). We can't simply depend on SKB_MODE
not being set because we may add more *_MODE flags in the future. So
doing:
if (flags & SKB_MODE)
printf("skb-mode");
else
printf("drv-mode");
is not correct. The flags attribute must not be present at all (think
HW_MODE flag). But going further there can also be non-MODE flags,
like, say.. NEVER_TX, and then there may be flags present in dump,
and if SKB_MODE isn't be set, the mode could be some new MODE user space
doesn't understand, or it could be DRV_MODE+a new non-MODE flag... no
way to tell :S
