Linux Virtualization - Mar 2019 - [RFC PATCH net-next] failover: allow name change on IFF_UP slave interfaces

On Tue, Mar 05, 2019 at 04:51:00PM -0800, si-wei liu
wrote:
> 
> 
> On 3/5/2019 4:36 PM, Michael S. Tsirkin wrote:
> > On Tue, Mar 05, 2019 at 04:20:50PM -0800, si-wei liu wrote:
> > > 
> > > On 3/5/2019 4:06 PM, Michael S. Tsirkin wrote:
> > > > On Tue, Mar 05, 2019 at 11:35:50AM -0800, si-wei liu wrote:
> > > > > On 3/5/2019 11:24 AM, Stephen Hemminger wrote:
> > > > > > On Tue, 5 Mar 2019 11:19:32 -0800
> > > > > > si-wei liu <si-wei.liu at oracle.com> wrote:
> > > > > > 
> > > > > > > > I have a vague idea: would it work to
*not* set
> > > > > > > > IFF_UP on slave devices at all?
> > > > > > > Hmm, I ever thought about this option, and it
appears this solution is
> > > > > > > more invasive than required to convert
existing scripts, despite the
> > > > > > > controversy of introducing internal netdev
state to differentiate user
> > > > > > > visible state. Either we disallow slave to be
brought up by user, or to
> > > > > > > not set IFF_UP flag but instead use the
internal one, could end up with
> > > > > > > substantial behavioral change that breaks
scripts. Consider any admin
> > > > > > > script that does `ip link set dev ... up'
successfully just assumes the
> > > > > > > link is up and subsequent operation can be
done as usual.
> > > > How would it work when carrier is off?
> > > > 
> > > > > While it *may*
> > > > > > > work for dracut (yet to be verified), I'm
a bit concerned that there are
> > > > > > > more scripts to be converted than those that
don't follow volatile
> > > > > > > failover slave names. It's technically
doable, but may not worth the
> > > > > > > effort (in terms of porting existing
scripts/apps).
> > > > > > > 
> > > > > > > Thanks
> > > > > > > -Siwei
> > > > > > Won't work for most devices.  Many devices
turn off PHY and link layer
> > > > > > if not IFF_UP
> > > > > True, that's what I said about introducing internal
state for those driver
> > > > > and other kernel component. Very invasive change
indeed.
> > > > > 
> > > > > -Siwei
> > > > Well I did say it's vague.
> > > > How about hiding IFF_UP from dev_get_flags (and probably
> > > > __dev_change_flags)?
> > > > 
> > > Any different? This has small footprint for the kernel change for
sure,
> > > while the discrepancy is still there. Anyone who writes code for
IFF_UP will
> > > not notice IFF_FAILOVER_SLAVE.
> > > 
> > > Not to mention more userspace "fixup" work has to be
done due to this
> > > change.
> > > 
> > > -Siwei
> > > 
> > > 
> > Point is it's ok since most userspace should just ignore slaves
> > - hopefully it will just ignore it since it already
> > ignores interfaces that are down.
> Admin script thought the interface could be bright up and do further
> operations without checking the UP flag.
These scripts then would be broken  on any box with multiple interfaces
since not all of these would have carrier.

> It doesn't look to be a reliable
> way of prohibit userspace from operating against slaves.
> 
> -Siwei
> 
> 
This does not mean we shouldn't make an effort to disable broken
configurations.

I am not arguing against your patch. Not at all. I see better
hiding of slaves as a separate enhancement.


Acked-by: Michael S. Tsirkin <mst at redhat.com>


-- 
MST