netdev - Re: what's in a bus

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Date:	Fri, 04 Nov 2011 16:31:24 -0700
From:	Rick Jones <rick.jones2@...com>
To:	Ben Hutchings <bhutchings@...arflare.com>
CC:	netdev@...r.kernel.org, rusty@...tcorp.com.au, mst@...hat.com
Subject: Re: what's in a bus_info

On 11/04/2011 04:02 PM, Ben Hutchings wrote:
> On Fri, 2011-11-04 at 15:27 -0700, Rick Jones wrote:
>> ...or would an interface name smell as sweet? (as PCI bus addressing)
>>
>> Is there a "standard" for what is returned in bus_info of
>> ethtool_drvinfo?  I have been very used to seeing PCI bus addressing
>> information in that field (at least as displayed by ethtool -i) and when
>> I went to "leverage how to" from other drivers, to add "native" ethtool
>> -i support to virtio_net, I ended-up with "eth0" rather than the PCI
>> information I see in lspci output and in ethtool -i against other
>> devices.  Including an emulated e1000 interface in the same kernel.
>>
>> What I'm doing is calling pci_name(), feeding it with to_pci_dev() from
>> the address of the struct device in the struct net_device.
>
> to_pci_dev() just uses container_of() to find a pci_dev when you have a
> pointer to the generic device structure embedded in it.  However, you're
> passing a pointer to the device embedded in a net_device.  The net
> device is a child of the PCI device, so you need to do:
>
> 	dev_dev = dev->dev.parent;
>
> And you don't even have to assume that the parent is a PCI device,
> because you can use the generic dev_name().
>
> But you don't even need to this, since the ethtool core has a default
> implementation that does this...

Yes, I noticed that.  For a little while I was confused because ethtool 
-i was emitting something even before I added a ".get_drvinfo" - though 
what it ends-up returning in my case is "virtio0." Which is also what I 
get if I take the path through the virtio_device to the struct device 
therein instead of the path through the struct net_device alone.

I guess that wraps back around to the question of whether there is a 
"standard" for what should be in bus_info.  And if it is impractical to 
get the PCI bus information, whether it is better to return virtioN or 
ethN.  Or perhaps something else entirely.

> [...]
>> BTW, I notice some drivers call strlcpy and some strncpy, and some even
>> call strcpy.  Is there one that is meant to be preferred over the others?
>
> strlcpy() is preferred - if it has to truncate, it will at least leave a
> null terminator, as clients may expect.  Back when drivers handled
> SIOCETHTOOL directly strncpy() may have been preferable since they were
> responsible for initialising the entire structure returned to
> user-space.

Thanks.  Perhaps that is another "floor sweeping" opportunity.

rick jones
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