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

[Igor Ryzhov <iryzhov@nfware.com>]

Hi again,

Forgot to mention netif_carrier_off changes. Your changes are necessary for
correct link status management,
but netif_carrier_off call should also be added to kni_ioctl_create before
the register_netdev call.
That's needed for correct link status even before first call to ndo_open.

Best regards,
Igor

On Thu, Aug 30, 2018 at 12:49 PM, 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
>
> On Thu, Aug 30, 2018 at 2:10 AM, Stephen Hemminger <
> stephen@networkplumber.org> wrote:
>
>> On Wed, 29 Aug 2018 19:41:23 -0300
>> Dan Gora <dg@adax.com> wrote:
>>
>> > On Wed, Aug 29, 2018 at 7:12 PM, Dan Gora <dg@adax.com> wrote:
>> > > On Wed, Aug 29, 2018 at 7:00 PM, Stephen Hemminger
>> > > <stephen@networkplumber.org> wrote:
>> > >>> >> Add a new API function to KNI, rte_kni_update_link() to allow
>> DPDK
>> > >>> >> applications to update the link state for the KNI network
>> interfaces
>> > >>> >> in the linux kernel.
>> > >>> >>
>> > >>> >> Note that the default carrier state is set to off when the
>> interface
>> > >>> >> is opened.
>> > >>> >>
>> > >>> >> Signed-off-by: Dan Gora <dg@adax.com>
>> > >>> >
>> > >>> > Do you really need a special ioctl for this?
>> > >>> > There is already ability to set link state via sysfs or netlink.
>> > >>>
>> > >>> I think yes.. AFAIK sysfs does not constitute a stable API;
>> > >>
>> > >> It is a stable API on Linux.
>> > >
>> >
>> > Actually this does not seem to be completely true...
>> >
>> > From Documentation/admin-guide/sysfs-rules.rst:
>> >
>> > Rules on how to access information in sysfs
>> > ===========================================
>> >
>> > The kernel-exported sysfs exports internal kernel implementation details
>> > and depends on internal kernel structures and layout. It is agreed upon
>> > by the kernel developers that the Linux kernel does not provide a stable
>> > internal API. Therefore, there are aspects of the sysfs interface that
>> > may not be stable across kernel releases.
>> >
>> > <snip>
>> >
>> > - devices are only "devices"
>> >     There is no such thing like class-, bus-, physical devices,
>> >     interfaces, and such that you can rely on in userspace. Everything
>> is
>> >     just simply a "device". Class-, bus-, physical, ... types are just
>> >     kernel implementation details which should not be expected by
>> >     applications that look for devices in sysfs.
>> >
>> >     The properties of a device are:
>> >
>> >     - devpath (``/devices/pci0000:00/0000:00:1d.1/usb2/2-2/2-2:1.0``)
>> > <snip>
>> >
>> >     - kernel name (``sda``, ``tty``, ``0000:00:1f.2``, ...)
>> > <snip>
>> >
>> >     - subsystem (``block``, ``tty``, ``pci``, ...)
>> > <snip>
>> >
>> >     - driver (``tg3``, ``ata_piix``, ``uhci_hcd``)
>> > <snip>
>> >
>> >     - attributes
>> > <snip>
>> >
>> >     Everything else is just a kernel driver-core implementation detail
>> >     that should not be assumed to be stable across kernel releases.
>>
>> Network device sysfs is stable. No one ever got around to putting it in
>> documentation
>> I wouldn't worry, once anything in /sys/class/net is added it is not
>> going to change without major breakage in many many tools.
>>
>
>