Re: [PATCH 2/2] e1000e: Make WOL info in ethtool consistent with device wake up ability

[Chen Yu]

Hi Michal,
Thanks for reviewing,
and sorry for late reply.
On Thu, May 21, 2020 at 09:23:42PM +0200, Michal Kubecek wrote:
> On Fri, May 22, 2020 at 01:59:13AM +0800, Chen Yu wrote:
> > Currently the ethtool shows that WOL(Wake On Lan) is enabled
> > even if the device wakeup ability has been disabled via sysfs:
> >   cat /sys/devices/pci0000:00/0000:00:1f.6/power/wakeup
> >    disabled
> > 
> >   ethtool eno1
> >   ...
> >   Wake-on: g
> > 
> > Fix this in ethtool to check if the user has explicitly disabled the
> > wake up ability for this device.
> 
> Wouldn't this lead to rather unexpected and inconsistent behaviour when
> the wakeup is disabled? As you don't touch the set_wol handler, I assume
> it will still allow setting enabled modes as usual so that you get e.g.
> 
>   ethtool -s eth0 wol g   # no error or warning, returns 0
>   ethtool eth0            # reports no modes enabled
> 
> The first command would set the enabled wol modes but that would be
> hidden from user and even the netlink notification would claim something
> different. Another exampe (with kernel and ethtool >= 5.6):
> 
>   ethtool -s eth0 wol g
>   ethtool -s eth0 wol +m
> 
> resulting in "mg" if device wakeup is enabled but "m" when it's disabled
> (but the latter would be hidden from user and only revealed when you
> enable the device wakeup).
> 
I've tested ethtool v5.6 on top of kernel v5.7-rc6, it looks like
the scenario you described will not happen as it will not allow
the user to enable the wol options with device wakeup disabled,
not sure if I missed something:

/sys/devices/pci0000:00/0000:00:1f.6/power# echo disabled > wakeup

ethtool -s eno1 wol g
netlink error: cannot enable unsupported WoL mode (offset 36)
netlink error: Invalid argument

I've not digged into the code too much, but according to
ethhl_set_wol(), it will first get the current wol options
via dev->ethtool_ops->get_wol(), and both the wolopts and
wol.supported are 0 when device wake up are disabled. Then
ethnl_update_bitset32 might manipulate on wolopts and
make it non-zero each is controdict with the precondition that
no opts should be enabled due to 0 wol.supported.
> This is a general problem discussed recently for EEE and pause
> autonegotiation: if setting A can be effectively used only when B is
> enabled, should we hide actual setting of A from userspace when B is
> disabled or even reset the value of A whenever B gets toggled or rather
> allow setting A and B independently? AFAICS the consensus seemed to be
> that A should be allowed to be set and queried independently of the
> value of B.

But then there would be an inconsistence between A and B. I was thinking
if there's a way to align them in kernel space and  maintain the difference in user space?

Thanks,
Chenyu
> 
> Michal
> 
> > Fixes: 6ff68026f475 ("e1000e: Use device_set_wakeup_enable")
> > Reported-by: Len Brown <len.brown@xxxxxxxxx>
> > Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> > Cc: <Stable@xxxxxxxxxxxxxxx>
> > Signed-off-by: Chen Yu <yu.c.chen@xxxxxxxxx>
> > ---
> >  drivers/net/ethernet/intel/e1000e/ethtool.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/ethernet/intel/e1000e/ethtool.c b/drivers/net/ethernet/intel/e1000e/ethtool.c
> > index 1d47e2503072..0cccd823ff24 100644
> > --- a/drivers/net/ethernet/intel/e1000e/ethtool.c
> > +++ b/drivers/net/ethernet/intel/e1000e/ethtool.c
> > @@ -1891,7 +1891,7 @@ static void e1000_get_wol(struct net_device *netdev,
> >  	wol->wolopts = 0;
> >  
> >  	if (!(adapter->flags & FLAG_HAS_WOL) ||
> > -	    !device_can_wakeup(&adapter->pdev->dev))
> > +	    !device_may_wakeup(&adapter->pdev->dev))
> >  		return;
> >  
> >  	wol->supported = WAKE_UCAST | WAKE_MCAST |
> > -- 
> > 2.17.1
> >