netdev - Re: [RFC][PATCH] Fix another namespace issue with devices assigned to classes

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Date:	Tue, 8 Jun 2010 16:47:57 +0200
From:	Kay Sievers <kay.sievers@...y.org>
To:	Johannes Berg <johannes@...solutions.net>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Greg KH <greg@...ah.com>, netdev <netdev@...r.kernel.org>
Subject: Re: [RFC][PATCH] Fix another namespace issue with devices assigned to 
	classes

On Tue, Jun 8, 2010 at 16:26, Johannes Berg <johannes@...solutions.net> wrote:
> On Tue, 2010-06-08 at 16:21 +0200, Kay Sievers wrote:
>
>> > Well they will be unregistered and everything, but once all the netdevs
>> > are gone etc. the devices you create in the patch might stick around
>> > because somebody has them open in sysfs, and I see nothing that would
>> > pin the module in that case?
>>
>> That's what I mean, I have no idea how to solve that with network
>> devices. I don't think any other subsytem allows to unload the module,
>> when devices, the module has created, are in use.
>
> You're right ... the would only be unregistered from your release, which
> would happen after the module is long gone ...
>
>> The current code uses the in-core class_create() logic, which was only
>> meant for devices with a device node, and which is cleaned up by the
>> core itself. That's why this issue never appeared before.
>>
>> But as said, I have no idea how to solve that with a single module. It
>> might not work at all without moving stuff into the core. That people
>> use device_create() with no major/minor might indicate that something
>> else is needed here. :)
>
> So ... can we apply Eric's patch for now then?

It might break other stuff we don't know about yet. Just like we did
not know about what things hwsim is doing here. :)

Eric's patch change the sysfs layout and insert directories into the
device path, and stuff which hardcodes things, or accesses devices
with ../<name> will break.

I don't mind trying it, but I wouldn't be surprised if that needs to
be reverted when issues caused by this appear.

The hwsim issues are caused by the current hwsim code, by doing things
it should not do. Class devices of different classes must never be
stacked (the core should not allow that in the first place). Class
devices must never have a driver assigned behind its back. Also
device_create() should not be used for devices without a major/minor
(but that seems to be done in several other places too).

To fix the hwsim driver core interaction, core changes will probably
be needed to allow network modules to be removed while their devices
are active. That's something which seems not to work for bus devices
currently.

Kay
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