Re: Requesting DLT_* values for Ethernet switches proprietary tagging protocol

[Guy Harris <gharris () sonic net>]

On Jan 17, 2019, at 7:49 PM, Florian Fainelli <f.fainelli () gmail com> wrote:

> Le 1/17/19 à 6:29 PM, Guy Harris a écrit :
> > On Jan 17, 2019, at 6:01 PM, Florian Fainelli <f.fainelli () gmail com> wrote:
> >
> > > Correct. The other ports are exposed as regular Ethernet network devices.
> >
> > OK, I've updated a comment in the pull request for that.
> >
> > So, in any pre-4.19 kernels, does the directory /sys/class/net/{device}/dsa exist even if there's no tagging file in 
> > that directory?
>
> Neither the directory nor the file actually exist.
>
> > Or is there some other way, in pre-4.19 kernels, to determine if a NIC is a DSA management-port NIC?
> >
> > If so, then, even though you can't determine the tag type from userland, you could offer all the DLT_s for the 
> > various tag types in the DLT list and let the user choose which one to use; they might be able to do so if they know 
> > what type of device they're capturing on.  (If the tagging file *does* exist, you can just offer them the one DLT_ 
> > that's correct for the device.)
>
> Good idea, people would certainly know which device they are capturing
> on. Thanks!

But if /sys/class/net/{device}/dsa doesn't exist in pre-4.19 kernels, how can you determine, from userland, whether a 
device is a DSA management-port NIC or not, in a system with a pre-4.19 kernel?  If you can't determine that, you can't 
know whether to offer a list of DSA management-port tag type DLTs or not.

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