Hotplugging ethernet cables.

Hotplugging ethernet cables.

[oliver]

After a quick search through the maillinglist archives I stumbled across 
http://marc.theaimsgroup.com/?t\x108195295700001&r=1&w=2

They mention ifplugd and even though this seems to work reasonably, I 
was wondering why hotplugging doesn't support ethernet hotplugging 
nativly? As I understand it the hotplugging daemon responds to events 
created by several devices, where the ifplugd polls and the device. Also 
this seems to fit perfectly into hotplugging as you plug something in :).
Also having a daemon for everything seems kinda normal these days, which 
I think is becoming out of hand.

Or is my gentoo installation just very misconfigured and does 
hotplugging indeed support ethernet cable hotplugging.

oliver


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Re: Hotplugging ethernet cables.

[Kay Sievers]

On Sun, 2005-01-02 at 02:11 +0100, oliver wrote:
> They mention ifplugd and even though this seems to work reasonably, I 
> was wondering why hotplugging doesn't support ethernet hotplugging 
> nativly?

Hotplug supports device add and remove, not state changes of hardware.

> As I understand it the hotplugging daemon responds to events 
> created by several devices, where the ifplugd polls and the device.

There is no such daemon involved in the hotplug handling. Hotplug is
driven by more or less stateless scripts invoked by the kernel.

The network link state changes can be received on a netlink socket from
the kernel. These events are not hotplug events and don't really fit
into the model of linux hotplug.

Kay




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Re: Hotplugging ethernet cables.

[Linas Vepstas]

Hi,

A naive question re ethernet hotplug:  what if its iSCSI?

On Sun, Jan 02, 2005 at 01:43:32AM +0100, Kay Sievers was heard to remark:
> On Sun, 2005-01-02 at 02:11 +0100, oliver wrote:
> > They mention ifplugd and even though this seems to work reasonably, I 
> > was wondering why hotplugging doesn't support ethernet hotplugging 
> > nativly?
> 
> Hotplug supports device add and remove, not state changes of hardware.
> 
> > As I understand it the hotplugging daemon responds to events 
> > created by several devices, where the ifplugd polls and the device.
> 
> There is no such daemon involved in the hotplug handling. Hotplug is
> driven by more or less stateless scripts invoked by the kernel.
> 
> The network link state changes can be received on a netlink socket from
> the kernel. These events are not hotplug events and don't really fit
> into the model of linux hotplug.


I can imagine  a scenario where Linux has mounted a filesystem that
is sitting on an iSCSI disk device.  Thus, in many respects, this is
analogous to a USB disk being plugged and unplugged.  I also presume
that iSCSI devices need not be just disks, but could be "anything",
thus making the situation even more analogous to USB.  

I'm also curious about plans for things like infiniband fabrics,
which might be plugged/unplugged in various ways, which the OS might
want to know about.  Again, this seems clearly analogous to USB fabrics
...


--linas


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Re: Hotplugging ethernet cables.

[Kay Sievers]

On Tue, 2005-01-04 at 11:44 -0600, Linas Vepstas wrote:
> A naive question re ethernet hotplug:  what if its iSCSI?
> 
> On Sun, Jan 02, 2005 at 01:43:32AM +0100, Kay Sievers was heard to remark:
> > On Sun, 2005-01-02 at 02:11 +0100, oliver wrote:
> > > They mention ifplugd and even though this seems to work reasonably, I 
> > > was wondering why hotplugging doesn't support ethernet hotplugging 
> > > nativly?
> > 
> > Hotplug supports device add and remove, not state changes of hardware.
> > 
> > > As I understand it the hotplugging daemon responds to events 
> > > created by several devices, where the ifplugd polls and the device.
> > 
> > There is no such daemon involved in the hotplug handling. Hotplug is
> > driven by more or less stateless scripts invoked by the kernel.
> > 
> > The network link state changes can be received on a netlink socket from
> > the kernel. These events are not hotplug events and don't really fit
> > into the model of linux hotplug.
> 
> 
> I can imagine  a scenario where Linux has mounted a filesystem that
> is sitting on an iSCSI disk device.  Thus, in many respects, this is
> analogous to a USB disk being plugged and unplugged.  I also presume
> that iSCSI devices need not be just disks, but could be "anything",
> thus making the situation even more analogous to USB.  

Sure, it's similar in some aspects, but linux-hotplug is only a device
"add" or "remove" notification. Every event corresponds to a created or
removed directory in /sys. There is no such thing for a network link.

If you add/remove the network device you get hotplug events. You don't
get hotplug events if you press a button of an USB device, which is very
similar to the network link state change. :)

Some networking applications produce a very high event traffic for state
changes - like the zebra routing daemon, this is definitely not possible
to do with the event-by-forked-helper-application-hotplug system. They
use the netlink socket for good reason. What do you think is the problem
to get network layer events over netlink? It works nicely this way for a
long time.

For a application level feature rich example, you may look how HAL is
collecting all available kernel events and offers a unified interface to
applications to subscribe to these events:
  http://cvs.freedesktop.org/*checkout*/hal/hal/doc/spec/hal-spec.html?rev=1.36.2.5

> I'm also curious about plans for things like infiniband fabrics,
> which might be plugged/unplugged in various ways, which the OS might
> want to know about.  Again, this seems clearly analogous to USB fabrics

Never seen such a thing. :)

Kay



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Re: Hotplugging ethernet cables.

[Oliver Schinagl]

What about SATA? sata is hotpluggable. And then, what if we have an 
external hdd rack via USB with a hot plugable sata connector in that. 
(as long as we don't have external sata connectors on laptops/PC's 
sounds reasonable)
Linux-hotplug would notice the USB event, while sata would have to deal 
with the hotplugging of the sata?

Also what about firewire? does linux-hotplugging handle firewire aswell? 
just curious ...

Kay Sievers wrote:

>On Tue, 2005-01-04 at 11:44 -0600, Linas Vepstas wrote:
>  
>
>>A naive question re ethernet hotplug:  what if its iSCSI?
>>
>>On Sun, Jan 02, 2005 at 01:43:32AM +0100, Kay Sievers was heard to remark:
>>    
>>
>>>On Sun, 2005-01-02 at 02:11 +0100, oliver wrote:
>>>      
>>>
>>>>They mention ifplugd and even though this seems to work reasonably, I 
>>>>was wondering why hotplugging doesn't support ethernet hotplugging 
>>>>nativly?
>>>>        
>>>>
>>>Hotplug supports device add and remove, not state changes of hardware.
>>>
>>>      
>>>
>>>>As I understand it the hotplugging daemon responds to events 
>>>>created by several devices, where the ifplugd polls and the device.
>>>>        
>>>>
>>>There is no such daemon involved in the hotplug handling. Hotplug is
>>>driven by more or less stateless scripts invoked by the kernel.
>>>
>>>The network link state changes can be received on a netlink socket from
>>>the kernel. These events are not hotplug events and don't really fit
>>>into the model of linux hotplug.
>>>      
>>>
>>I can imagine  a scenario where Linux has mounted a filesystem that
>>is sitting on an iSCSI disk device.  Thus, in many respects, this is
>>analogous to a USB disk being plugged and unplugged.  I also presume
>>that iSCSI devices need not be just disks, but could be "anything",
>>thus making the situation even more analogous to USB.  
>>    
>>
>
>Sure, it's similar in some aspects, but linux-hotplug is only a device
>"add" or "remove" notification. Every event corresponds to a created or
>removed directory in /sys. There is no such thing for a network link.
>
>If you add/remove the network device you get hotplug events. You don't
>get hotplug events if you press a button of an USB device, which is very
>similar to the network link state change. :)
>
>Some networking applications produce a very high event traffic for state
>changes - like the zebra routing daemon, this is definitely not possible
>to do with the event-by-forked-helper-application-hotplug system. They
>use the netlink socket for good reason. What do you think is the problem
>to get network layer events over netlink? It works nicely this way for a
>long time.
>
>For a application level feature rich example, you may look how HAL is
>collecting all available kernel events and offers a unified interface to
>applications to subscribe to these events:
>  http://cvs.freedesktop.org/*checkout*/hal/hal/doc/spec/hal-spec.html?rev=1.36.2.5
>
>  
>
>>I'm also curious about plans for things like infiniband fabrics,
>>which might be plugged/unplugged in various ways, which the OS might
>>want to know about.  Again, this seems clearly analogous to USB fabrics
>>    
>>
>
>Never seen such a thing. :)
>
>Kay
>
>  
>


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