Re: Legacy Linux kernel support

[Mario Rugiero <mrugiero () gmail com>]

El lun., 7 oct. 2019 a las 12:32, Michael Richardson
(<mcr+ietf () sandelman ca>) escribió:
> Mario Rugiero <mrugiero () gmail com> wrote:
>     > The 'pcap-linux.c' implementation is plagued by #ifdefs and special
>     > cases aiming to support kernels as old as the 2.0.x family era.
>     > The oldest version supported by upstream is 3.16.74.
>
>     > The most 'bleeding-edge' supported family has been there since the
>     > 2.6.y times, almost 10 years ago, so I think we can assume it's
>     > present on any current user's box.
>
> So what would be the oldest kernel that your revised code would support?
> I'm reading 3.16?
Yes. Probably older, but as a side effect only, and I wouldn't like that support
to be advertised.
>     > Anybody not upgrading the kernel for as long is very unlikely to want
>     > to update libpcap.
>
> Well, that's not really true.
> There are many cases where people have to debug some silly appliance
> that has been locked down to some 2.6 (or 2.4 due to binary blog drivers)
> kernel.  They often have to build libpcap/tcpdump elsewhere and copy the
> binary over.
>
> Reasonably, though, they could probably build an old version of libpcap.
> So, I would ask that the simplified code point to the last version of libpcap
> (1.9) that will work in the error message.  Your revision could be in 1.10.
That's reasonable.
We could report it at runtime checking `uname` and at build time by checking
`#ifdef`s and throwing a build time error.
>     > I think it would be useful to have the closest to a single build that
>     > we can get.
>     > I get having different builds for different user facing features
>     > (sniffing USB, for example), but not for something the user generally
>     > won't know, such as if the kernel where libpcap was built supported
>     > TPACKET V2 or V3.
>
> Yes, so the USB sniffer is not in pcap-linux.c, but pcap-usb-linux.c, and I
> don't think you propose to change that.
Indeed, I'm not proposing touching that.
>     > In the same note, assuming an environment from this decade brings us
>     > some possibilities to write simpler and shorter code.
>     > For example, querying the present interfaces becomes way easier
>     > calling if_nameindex than the current crawl through sysfs.
>
> +1
>
> Now that 1.9.1 is out, now is a great time to do this.
> I will attempt to crawl through pull requests that update pcap-linux.c, and
> see if there is any low-hanging fruit that we should merge before you
> cleanup. I will make some tag for this.  You may want to go ahead of me, as I
> won't start before oct. 14, probably finish wednesday Oct. 16.
Great, I'll try to start this week.
> --
> Michael Richardson <mcr+IETF () sandelman ca>, Sandelman Software Works
>  -= IPv6 IoT consulting =-
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