netdev - Re: [RFC] RESEND - rdmatool

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Date:   Thu, 19 Jan 2017 11:03:08 -0700
From:   Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:     Leon Romanovsky <leon@...nel.org>
Cc:     Bart Van Assche <bart.vanassche@...disk.com>,
        Or Gerlitz <gerlitz.or@...il.com>,
        Ariel Almog <arielalmogworkemails@...il.com>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
        Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: [RFC] RESEND - rdmatool - tool for RDMA users

On Thu, Jan 19, 2017 at 08:33:26AM +0200, Leon Romanovsky wrote:
> On Wed, Jan 18, 2017 at 01:45:14PM -0800, Bart Van Assche wrote:
> > On 01/18/2017 10:31 AM, Jason Gunthorpe wrote:
> > > I think it depends on what this tool is supposed to cover, but based
> > > on the description, I would start with netlink-only.
> > >
> > > The only place verbs covers a similar ground is in 'device
> > > capabilities' - for some of that you might want to open a new-uAPI
> > > verbs fd, but even the capability data from that would not be
> > > totally offensive to be accessed over netlink.
> > >
> > > IMHO netlink should cover almost everything found in sysfs today.
> >
> > We would need a very strong argument to introduce a netlink API that
> > duplicates existing sysfs API functionality. Since the sysfs API is
> > extensible, why not extend that API further? E.g. the SCST sysfs API
> > shows that more is possible with sysfs than what most kernel drivers
> > realize.
> 
> We didn't look deeply on sysfs mainly because it is unpopular
> in netdev community. Maybe we were misled and it is simply not true.

sysfs is unpopular because the 'one value per file' dogma is laregly
unsuitable for complex mulit-value atomic changes which are common in
netdev. You can force it to work, but it is pretty horrible..

It is also very expensive if you want to shuttle a lot of data, eg I
could not see doing something like 'netstat' for IB through sysfs

Maybe you should start by showing some examples of command out you
wish to have in a rdmatool ..

Jason