[dpdk-stable] [dpdk-dev] [PATCH] net/af_xdp: fix support of secondary process

[Stephen Hemminger]

On Mon, 20 Sep 2021 13:23:57 +0000
"Loftus, Ciara" <ciara.loftus at intel.com> wrote:

> > -----Original Message-----
> > From: dev <dev-bounces at dpdk.org> On Behalf Of Stephen Hemminger
> > Sent: Friday 3 September 2021 17:15
> > To: dev at dpdk.org
> > Cc: Stephen Hemminger <stephen at networkplumber.org>;
> > stable at dpdk.org; xiaolong.ye at intel.com
> > Subject: [dpdk-dev] [PATCH] net/af_xdp: fix support of secondary process
> > 
> > Doing basic operations like info_get or get_stats was broken
> > in af_xdp PMD. The info_get would crash because dev->device
> > was NULL in secondary process. Fix this by doing same initialization
> > as af_packet and tap devices.
> > 
> > The get_stats would crash because the XDP socket is not open in
> > primary process. As a workaround don't query kernel for dropped
> > packets when called from secondary process.
> > 
> > Note: this does not address the other bug which is that transmitting
> > in secondary process is broken because the send() in tx_kick
> > will fail because XDP socket fd is not valid in secondary process.  
> 
> Hi Stephen,
> 
> Apologies for the delayed reply, I was on vacation.
> 
> In the Bugzilla report you suggest we:
> "mark AF_XDP as broken in with primary/secondary
> and return an error in probe in secondary process".
> I agree with this suggestion. However with this patch we still permit secondary, and just make sure it doesn't crash for get_stats. Did you change your mind?
> Personally, I would prefer to have primary/secondary either working 100% or else not allowed at all by throwing an error during probe. What do you think? Do you have a reason/use case to permit secondary processes despite some features not being available eg. full stats, tx?
> 
> Thanks,
> Ciara

There are two cases where secondary is useful even if send/receive can't work from secondary process.
The pdump and proc-info applications can work with these patches.

I am using XDP over pdump as an easy way to get packets into the code for testing.

The flag in the documentation doesn't have a "limited" version.
If you want, will send another patch to disable secondary support.

Supporting secondary, means adding a mechanism to pass the socket around.