Re: [dpdk-dev] [PATCH v2 10/10] kni: add API to set link status on kernel interface

[Dan Gora <dg@adax.com>]

Hi All,

So I'm a little unclear as to what to do here moving forward..

Do we all agree at least that there should be some function in DPDK in
order to set the link state for KNI interfaces?

I'm a strong yes on this point.  I don't think that every KNI user
should have to implement something like this themselves if we can
provide a simple interface to do it.  It seems like a natural
extension of the KNI functionality IMHO.

If so, should we use a new ioctl as in my patch, or just use the
"write to /sys.../carrier" method as shown below?

I'm kind of ambivalent about this point.  The ioctl method has two
minor advantages to my mind:

1) It's already done :)

2) You can set the link speed and duplex as well and get a pretty
message in the syslog when the link status changes:

[ 2100.016079] rte_kni: adax0 NIC Link is Up 10000 Mbps Full Duplex.
[ 2100.016094] IPv6: ADDRCONF(NETDEV_CHANGE): adax0: link becomes ready
[ 2262.532126] IPv6: ADDRCONF(NETDEV_UP): adax1: link is not ready
[ 2263.432148] rte_kni: adax1 NIC Link is Up 10000 Mbps Full Duplex.
[ 2263.432170] IPv6: ADDRCONF(NETDEV_CHANGE): adax1: link becomes ready

On the other hand, the "write to /sys" method is a bit more simple and
confines the changes to the user space library.  If we're confident
that the /sys ABI is stable and not going to be changed going forward
it seems like a valid alternative.

I'm willing to do it either way.  I'll defer to the judgement of the
community...

thanks
dan


On Thu, Aug 30, 2018 at 6:49 AM, Igor Ryzhov <iryzhov@nfware.com> wrote:
> Hi Dan,
>
> We use KNI device exactly the same way you described – with IP addresses,
> routing, etc.
> And we also faced the same problem of having the actual link status in Linux
> kernel.
>
> There is a special callback for link state management in net_device_ops for
> soft-devices like KNI called ndo_change_carrier.
> Current KNI driver implements it already, you just need to write to
> /sys/class/net/<iface>/carrier to change link status.
>
> Right now we implement it on application side, but I think it'll be good to
> have this in rte_kni API.
>
> Here is our implementation:
>
> static int
> linux_set_carrier(const char *name, int status)
> {
> char path[64];
> const char *carrier = status ? "1" : "0";
> int fd, ret;
>
> sprintf(path, "/sys/devices/virtual/net/%s/carrier", name);
> fd = open(path, O_WRONLY);
> if (fd == -1) {
> return -errno;
> }
>
> ret = write(fd, carrier, 2);
> if (ret == -1) {
> close(fd);
> return -errno;
> }
>
> close(fd);
>
> return 0;
> }
>
> Best regards,
> Igor