writeups for hotplugging S/390 chandev, PNP docking stations?

writeups for hotplugging S/390 chandev, PNP docking stations?

[David Brownell]

I notice that those two subsystems are now hotplug
enabled ... chandev in both 2.4 and 2.5, and the
docking station support in 2.5.7 (and maybe earlier).

Anyone know where there are writeups for those?
I want to keep the website reasonably complete
with regards to hotplug support in "official" kernels.
Documentation/s390/chandev.8 talks a bit about
that, but it's rather cryptic.  And I didn't see any
info about the docking station support.

Also, let us know if there are hotplug scripts that
should be incorporated into the standard toolset.

I'd suspect they'd be more generally useful for the
laptop docking stations than for the mainframes,
but I could easily get surprised!  :)

- Dave

http://linux-hotplug.sourceforge.net






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Re: writeups for hotplugging S/390 chandev, PNP docking stations?

[Rick Troth]

I've sent to Mark Post,  one of the info reference people 
in the S/390 (aka: zSeries) community.   Mark should be able to 
recommend someone who can clear-up the description.   This "chandev.8" 
probably came out of the lab that produces most of the S/390 patches. 
Their focus is on code,  I'm sure,  not doc.   But someone who 
understands the princ. of ops can probably make it plain. 
 
> Also, let us know if there are hotplug scripts that
> should be incorporated into the standard toolset.
> 
> I'd suspect they'd be more generally useful for the
> laptop docking stations than for the mainframes,
> but I could easily get surprised!  :)
 
Surprise!   The mainframe plugs and un-plugs all the time. 
Devices get  "varied online"  (or offline)  on demand. 
The situation only gets worse when you're running Linux in a 
virtual machine where one could  'hcp attach'  (or detach) 
things on-the-fly,  both virtual and real.   It's fun! 
 
Let's just say that the mainframe Linux crowd 
has been waiting for hotplug for a long time.   :-) 
Rebooting just to recognize a dynamic device is ... sub-optimal.   :-( 
 



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Re: writeups for hotplugging S/390 chandev, PNP docking stations?

[David Brownell]

> > Also, let us know if there are hotplug scripts that
> > should be incorporated into the standard toolset.
> > 
> > I'd suspect they'd be more generally useful for the
> > laptop docking stations than for the mainframes,
> > but I could easily get surprised!  :)
>  
> Surprise!   The mainframe plugs and un-plugs all the time. 

... actually I meant that in the sense that there are
more Linux laptops than Linux mainframes ... though
I'm sure some vendors would gladly change that
particular dynamic!  :)


> Let's just say that the mainframe Linux crowd 
> has been waiting for hotplug for a long time.   :-) 
> Rebooting just to recognize a dynamic device
> is ... sub-optimal.   :-( 

I seem to recall mentioning that to Linus way back
when I did the initial version of hotplug.  As you
imply, high availability servers need to really value
their uptime, and "hot" reconfiguration is key to
getting past just "five nines" into _really_ high
system availability ... 

- Dave




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Re: writeups for hotplugging S/390 chandev, PNP docking stations ?

[David Brownell]

> I normally use the "Device Drivers and Installation Commands" document when
> I want to refresh my memory on a particular command for a particular type of
> device.
> (http://www10.software.ibm.com/developerworks/opensource/linux390/docu/l390dd07.pdf)

Luckily Acrobat has a "find", and the hotplug discussion starts at the
front of chapter 8.  (It's not in the index or TOC ... :)

The hotplug script there doesn't follow the conventions of the
linux-hotplug project; that'd involve "/etc/hotplug/chandev.agent"
as the script doing the magic.  Which means that the network
hotplug events will get ignored ... why is that?  Seems to me
more natural to do network administration through network
hotplug events, not chandev ones!  (The /sbin/hotplug script
normally delegates the work to /etc/hotplug/$1.agent ...)


> This seems pretty clear and reasonably well-written.  If Dave
> finds this more acceptable, then I guess we're done.

I believe there's a bunch left unsaid there about what the
device names indicate.  I'd hope that eth0/eth1/eth2 are all
Ethernet, and that tr0 is token ring (it still lives? :), but I have
no clue what "ctc0" would be or, in general, how and what
those names are.  Wouldn't disk drives show up there?
And tape backup units, etc?

What I'll do is stick a pointer to it, and update the linux-hotplug
webpage about "chandev" to present some of that info.  My
understanding is that the management of mainframes has its
own families of idiosyncracies, developed over decades, that
it's not worth my time to master ... :)  For now I'm happy just
to keep the subsystem information current on the web

- Dave



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RE: writeups for hotplugging S/390 chandev, PNP docking stations ?

[Rick Troth]

> The hotplug script there doesn't follow the conventions of the
> linux-hotplug project; that'd involve "/etc/hotplug/chandev.agent"
> as the script doing the magic.  Which means that the network
> hotplug events will get ignored ... why is that?  Seems to me
> more natural to do network administration through network
> hotplug events, not chandev ones!  (The /sbin/hotplug script
> normally delegates the work to /etc/hotplug/$1.agent ...)
 
I can't speak to this, 
but I'm sure the S/390 subdivision of the Linux community 
would like to see it fixed. 
 
> I believe there's a bunch left unsaid there about what the
> device names indicate.  I'd hope that eth0/eth1/eth2 are all
> Ethernet, 
 
Yes. 
 
>           and that tr0 is token ring (it still lives? :), but I have
 
Token ring,  yes.   Still lives in some corners. 
 
> no clue what "ctc0" would be or, in general, how and what
> those names are.  Wouldn't disk drives show up there?
> And tape backup units, etc?
 
CTC is "channel-to-channel" which is a point-to-point thing 
conceptually like two SCSI chains having a bridge between them. 
 
Mainframe also has a network interface known as IUCV 
(iucv0, iucv1, etc),  but that has no representation in real hardware 
so I don't know if it would really fit in the "chandev" suite. 
 
> What I'll do is stick a pointer to it, and update the linux-hotplug
> webpage about "chandev" to present some of that info.  My
> understanding is that the management of mainframes has its
> own families of idiosyncracies, developed over decades, that
> it's not worth my time to master ... :)  For now I'm happy just
> to keep the subsystem information current on the web
 
Thanks for keeping it current. 
I for one very much value the commonality 
and hope that S/390 will be able to use most of this infrastructure 
rather than re-invent it. 
 


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