2.5.47bk2 + current modutils == broken hotplug

2.5.47bk2 + current modutils == broken hotplug

[David Brownell]

The module-init-tools-0.6.tar.gz utilities (or something
related -- kbuild changes?) break hotplug since they no
longer produce the /lib/modules/$(uname -r)/modules.*map
files as output ... so the hotplug agents don't have the
pre-built database mapping device info to drivers.

What's the plan for getting that back?  (And module.conf
params etc.)  "Changes" says version 2.4.2 is fine, which
appears to be wrong...

- Dave

Re: 2.5.47bk2 + current modutils == broken hotplug

[Greg KH]

On Wed, Nov 13, 2002 at 12:11:01PM -0800, David Brownell wrote:
> The module-init-tools-0.6.tar.gz utilities (or something
> related -- kbuild changes?) break hotplug since they no
> longer produce the /lib/modules/$(uname -r)/modules.*map
> files as output ... so the hotplug agents don't have the
> pre-built database mapping device info to drivers.

Last I heard, Rusty's still working on this.  He's also going to be
changing the format so we don't expose kernel structures to userspace,
which would be a good thing.

In short, he knows this is a requirement, and shouldn't be broken for
long.

thanks,

greg k-h

Re: 2.5.47bk2 + current modutils == broken hotplug

[David Brownell]

Greg KH wrote:
> On Wed, Nov 13, 2002 at 12:11:01PM -0800, David Brownell wrote:
> 
>>The module-init-tools-0.6.tar.gz utilities (or something
>>related -- kbuild changes?) break hotplug since they no
>>longer produce the /lib/modules/$(uname -r)/modules.*map
>>files as output ... so the hotplug agents don't have the
>>pre-built database mapping device info to drivers.
> 
> 
> Last I heard, Rusty's still working on this.  He's also going to be
> changing the format so we don't expose kernel structures to userspace,
> which would be a good thing.

So long as the _information_ in those structures stays available, good.
And it'd be handy if the text format for that information didn't change;
how it's stored in object modules doesn't matter.


> In short, he knows this is a requirement, and shouldn't be broken for
> long.

Good, that's important.

- Dave


> thanks,
> 
> greg k-h
> 

Re: 2.5.47bk2 + current modutils == broken hotplug

[Jeff Garzik]

David Brownell wrote:

> Greg KH wrote:
>
> > On Wed, Nov 13, 2002 at 12:11:01PM -0800, David Brownell wrote:
> >
> >> The module-init-tools-0.6.tar.gz utilities (or something
> >> related -- kbuild changes?) break hotplug since they no
> >> longer produce the /lib/modules/$(uname -r)/modules.*map
> >> files as output ... so the hotplug agents don't have the
> >> pre-built database mapping device info to drivers.
> >
> >
> >
> > Last I heard, Rusty's still working on this.  He's also going to be
> > changing the format so we don't expose kernel structures to userspace,
> > which would be a good thing.
>
>
> So long as the _information_ in those structures stays available, good.


Agreed.

> And it'd be handy if the text format for that information didn't change;
> how it's stored in object modules doesn't matter.



Correction -- the tools that read the text format are buggy if they do 
not transparently support changes to the text format.
(Corollary: the text format is buggy if it does not support a method of 
noticing format changes)

I am planning on adding PCI revision id to the information exported via 
MODULE_DEVICE_TABLE(pci,...).  Tools which correctly read the 
first-line-format-definition will continue to function as before, 
regardless of additional fields I want to add.  Tools which make silly 
assumptions will have those assumptions come back to bite them ;-)

(tangent warning!)
Another long term idea I would eventually like to realize is the removal 
of device ids from the C source code.  I don't care where they go -- 
drivers/net/pci_ids [per directory ids?], drivers/net/3c59x.meta, 
whereever.  Anywhere but the C source code.  It's quite silly to require 
a driver rebuild just to add a single PCI id, and further, embedding 
metadata in C source is rarely a good idea in the long term.  [reference 
some of Linus's counter-arguments when it was mentioned that Donald 
Becker's method of including Config.{in,help} data in C source might be 
useful]

	Jeff

Re: 2.5.47bk2 + current modutils == broken hotplug

[Greg KH]

On Wed, Nov 13, 2002 at 03:59:56PM -0500, Jeff Garzik wrote:
> 
> (tangent warning!)
> Another long term idea I would eventually like to realize is the removal 
> of device ids from the C source code.  I don't care where they go -- 
> drivers/net/pci_ids [per directory ids?], drivers/net/3c59x.meta, 
> whereever.  Anywhere but the C source code.  It's quite silly to require 
> a driver rebuild just to add a single PCI id, and further, embedding 
> metadata in C source is rarely a good idea in the long term.  [reference 
> some of Linus's counter-arguments when it was mentioned that Donald 
> Becker's method of including Config.{in,help} data in C source might be 
> useful]

True, this would be nice, but how would the driver know to bind to a new
device, if it isn't rebuilt, and doesn't know about the new id that was
just added?  In the current scheme of driver matching to devices, I
don't see how this could be done.

Not to say I would not want to see this changed to allow this to happen,
I'm very tired of telling USB Palm users to get a new kernel version
just because a single device id was added which their new device has.

thanks,

greg k-h

Re: 2.5.47bk2 + current modutils == broken hotplug

[David Brownell]

>> And it'd be handy if the text format for that information didn't change;
>> how it's stored in object modules doesn't matter.
> 
> Correction -- the tools that read the text format are buggy if they do 
> not transparently support changes to the text format.

That's not a correction, it's a tangent!   Either way, it's still
"handy" ... since supporting new formats requires new tools, and it's
clearly "handy" not to need to write, debug, and deploy new tools
(including teaching, documenting, etc).

> I am planning on adding PCI revision id to the information exported via 
> MODULE_DEVICE_TABLE(pci,...).  Tools which correctly read the 
> first-line-format-definition will continue to function as before, 
> regardless of additional fields I want to add.  Tools which make silly 
> assumptions will have those assumptions come back to bite them ;-)

The "silly assumption" seems to be that the current "modules.*map"
format can reasonably be extended ... when no rules for extending those
file formats were really defined, and the _only_ precedent for even
changing them involved incompatibility between "versions".

I'd far rather have a decent file format for that data, and move
away from that ungainly syntax, than try to retrofit rules about
how to extend that syntax.  Such a format should:

  - allow comments
  - not have as much garbage (zeroes, 0xffffffff, etc)
  - still be easily parsable from shell scripts (*)
  - be easier for site admins to edit (insert vi/emacs flamewar)
  - have an explicit version code, and rules about evolution

Alternatively, the tried'n'true approach of coupling the format
to the filename works:  don't reuse "modules.*map", use "*.modules"
or something.
- Dave

(*) This is the annoying requirement.  Maybe worth relaxing.
     For example, an XML format could easily support all the
     other requirements ... but not (AFAIK) that one.

Re: 2.5.47bk2 + current modutils == broken hotplug

[Jeff Garzik]

Greg KH wrote:

> On Wed, Nov 13, 2002 at 03:59:56PM -0500, Jeff Garzik wrote:
>
> >(tangent warning!)
> >Another long term idea I would eventually like to realize is the removal
> >of device ids from the C source code.  I don't care where they go --
> >drivers/net/pci_ids [per directory ids?], drivers/net/3c59x.meta,
> >whereever.  Anywhere but the C source code.  It's quite silly to require
> >a driver rebuild just to add a single PCI id, and further, embedding
> >metadata in C source is rarely a good idea in the long term.  [reference
> >some of Linus's counter-arguments when it was mentioned that Donald
> >Becker's method of including Config.{in,help} data in C source might be
> >useful]
>
>
> True, this would be nice, but how would the driver know to bind to a new
> device, if it isn't rebuilt, and doesn't know about the new id that was
> just added?  In the current scheme of driver matching to devices, I
> don't see how this could be done.


I think that truly seamless rebinding is doable but would require too 
much additional complexity in the kernel.  Rebinding to a new id table 
between unregister() ... register() pairs, or between mod unload and mod 
load, should be enough to be useable for 98% of the cases.

It should be noted that David Hinds' pcmcia-cs package stores id in an 
external database.  There are both positive and negative lessons that 
have been learned from that experience (WRT external id tables only! 
:):)) too.


> Not to say I would not want to see this changed to allow this to happen,
> I'm very tired of telling USB Palm users to get a new kernel version
> just because a single device id was added which their new device has.


Indeed :/  There are also issues like vendors who want to GPG-sign 
drivers, and updating the PCI id table makes the GnuPG signature and the 
certification that goes along with it invalid, requiring a vendor update.

	Jeff

Re: 2.5.47bk2 + current modutils == broken hotplug

[David Brownell]

Jeff Garzik wrote:
> Greg KH wrote:
> 
>> On Wed, Nov 13, 2002 at 03:59:56PM -0500, Jeff Garzik wrote:
>>
>> >(tangent warning!)
>> >Another long term idea I would eventually like to realize is the removal
>> >of device ids from the C source code.  ...

Hmm, maybe Linux should use Microsoft's ".inf" file syntax?  %-)

That's one thing that it achieves, at the cost of serious chaos
when the files with the device IDs get out of sync with the
drivers they supposedly work with.


>> True, this would be nice, but how would the driver know to bind to a new
>> device, if it isn't rebuilt, and doesn't know about the new id that was
>> just added?  In the current scheme of driver matching to devices, I
>> don't see how this could be done.

It'd be good if we had ways that user mode tools can request drivers be
bound and un-bound.  "usbfs" has some support for that, not exactly
packaged in the way I'd most like (and "usbfs" is problematic too).


> I think that truly seamless rebinding is doable but would require too 
> much additional complexity in the kernel.  Rebinding to a new id table 
> between unregister() ... register() pairs, or between mod unload and mod 
> load, should be enough to be useable for 98% of the cases.

I'd rather not try swapping ID tables ... likely better to keep some
of that information compiled in to the drivers, but also ADD ways that
user mode tools can modify the bindings that the kernel does (or doesn't)
establish.  Unless someone wants to get radical and insist that ONLY the
user mode tools can define such policies (after bootstrapping is done).

Of course Greg's example of a Palm could be addressed using current
infrastructure and module parameters, with "wildcard" binding (to
make sure the driver can see if the device matches the parameters).

- Dave

Re: 2.5.47bk2 + current modutils == broken hotplug

[Rusty Russell]

In message <3DD2B1D5.7020903@pacbell.net> you write:
> The module-init-tools-0.6.tar.gz utilities (or something
> related -- kbuild changes?) break hotplug since they no
> longer produce the /lib/modules/$(uname -r)/modules.*map
> files as output ... so the hotplug agents don't have the
> pre-built database mapping device info to drivers.

Sorry, I've been feeding Linus (and lkml) slowly.  It's not permenant,
I promise 8) I discussed the issue with Greg Kroah-Hartman and have
sent him a patch for examination.  In the new method, external code
doesn't know about kernel datastructures.

> What's the plan for getting that back?  (And module.conf
> params etc.)

The question is whether to force an /sbin/hotplug change to use the
module alias mechanism, or generate the modules.*map files at "make
modules_install" time to avoid breakage.  I'm leaning towards #2, but
I haven't written it yet (should be simple).

0.7 has preliminary /etc/modprobe.conf support, but it only does
primitive aliases not options as yet.  That's next on my list for
userspace, along with "modprobe -r".

> "Changes" says version 2.4.2 is fine, which appears to be wrong...

Thanks for the feedback,
Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.

Re: 2.5.47bk2 + current modutils == broken hotplug

[David Brownell]

>>What's the plan for getting that back?  (And module.conf
>>params etc.)
> 
> 
> The question is whether to force an /sbin/hotplug change to use the
> module alias mechanism, or generate the modules.*map files at "make
> modules_install" time to avoid breakage.  I'm leaning towards #2, but
> I haven't written it yet (should be simple).

Yes, please.  The kmod style aliasing presumes the answer to
"what do I do with this device?" is "load these modules", which
makes answers like "mount the disk" or "start this daemon/driver"
needlessly hard to achieve.

Hotplugging may well change more in 2.5, but I'd rather have it do
so on a more flexible schedule than "quick, before 2.5.48 ships"!  :)


> 0.7 has preliminary /etc/modprobe.conf support, but it only does
> primitive aliases not options as yet.  That's next on my list for
> userspace, along with "modprobe -r".
> 
> 
>>"Changes" says version 2.4.2 is fine, which appears to be wrong...
> 
> 
> Thanks for the feedback,

Thanks for the info ... it didn't seem very visible, so I wanted
to know what the story was!  Heck, I'm just glad to see forward
motion in the module load/unload area.

Is it true that the infrastructure newly in place can easily be
made to provide (from user-space) the policy of "driver remains
loaded until the devices it's bound to are all unplugged"?

That'd be a user-friendly policy, but we'd still need to handle
today's developer-oriented "sysadmin can always remove module"
policy.  (Me, I'd run with the "user friendly" policy except
when hacking a driver.  Then I'd debug/rmmod/update/modprobe.)

- Dave



> Rusty.
> --
>   Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
> 

Re: 2.5.47bk2 + current modutils == broken hotplug

[Rusty Russell]

In message <3DD3589C.5000002@pacbell.net> you write:
> Hotplugging may well change more in 2.5, but I'd rather have it do
> so on a more flexible schedule than "quick, before 2.5.48 ships"!  :)

Hey, I want to get humpty dumpty back together ASAP, too.  But I'm in
Spain without an x86 box (my test box is available though a modem to
IBM's intranet, two ssh's away), so it's a little difficult for me,
too.  And I'm still catching up on mail.

> Is it true that the infrastructure newly in place can easily be
> made to provide (from user-space) the policy of "driver remains
> loaded until the devices it's bound to are all unplugged"?

That should always be true, unless I'm missing something.  What kind
of devices?

> That'd be a user-friendly policy, but we'd still need to handle
> today's developer-oriented "sysadmin can always remove module"
> policy.  (Me, I'd run with the "user friendly" policy except
> when hacking a driver.  Then I'd debug/rmmod/update/modprobe.)

rmmod -f is about as unfriendly as you can get, really 8)

Cheers,
Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.

Re: 2.5.47bk2 + current modutils == broken hotplug

[David Brownell]

This is about another of the limitations/flaws of the current
module framework, which I'm hoping the new one could fix...


>>Is it true that the infrastructure newly in place can easily be
>>made to provide (from user-space) the policy of "driver remains
>>loaded until the devices it's bound to are all unplugged"?
> 
> 
> That should always be true, unless I'm missing something.  What kind
> of devices?

Any device whose driver gets modprobed through hotplug ... it'd
be good to have the module unload automatically when the hardware
is gone.  The pcmcia tools do this already, with a more limited
problem domain, by tracking device-to-driver associations in the
kernel.  But other hotpluggable frameworks can't do it today, and
it seems to be the module framework which gets in the way.


Consider two instances of such a device.  Hotplug one, the driver
is loaded, refcount zero since it's not opened.  Then rmmod on
unplug would be appropriate:  the hardware is gone.

But instead of unplugging it, plug in a second.  Now rmmod is no
longer an appropriate default policy on unplug, even though the
module "refcount" is still zero, since the user could still try
access the other device.  (Maybe they were plugging in devices
until they found the one with the data they were after, and just
hadn't looked at that the other one yet.)


It's a case where the current modprobe/rmmod scheme is counting
the wrong kinds of things.  Changing module refcounts to track the
device bindings would be a "hard" policy, interfering with driver
developer and sysadmins (gotta reboot or unplug to change drivers).
Tracking such device-to-driver bindings in userland is fragile.
Today's workaround is not to rmmod ... an undesirable answer.

So I keep thinking the right answer is to have a separate count
to track hardware bindings, or at any rate some "soft" policy
hook is needed to prevent rmmod in such cases.  Sysadmins and
driver developers would be able to override the policy, but
Joe Tux-user would just stick to the default.

- Dave


>>That'd be a user-friendly policy, but we'd still need to handle
>>today's developer-oriented "sysadmin can always remove module"
>>policy.  (Me, I'd run with the "user friendly" policy except
>>when hacking a driver.  Then I'd debug/rmmod/update/modprobe.)
> 
> 
> rmmod -f is about as unfriendly as you can get, really 8)
> 
> Cheers,
> Rusty.
> --
>   Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
> 

Re: 2.5.47bk2 + current modutils == broken hotplug

[Rusty Russell]

In message <3DD3CD08.7080003@pacbell.net> you write:
> Consider two instances of such a device.  Hotplug one, the driver
> is loaded, refcount zero since it's not opened.  Then rmmod on
> unplug would be appropriate:  the hardware is gone.
> 
> But instead of unplugging it, plug in a second.  Now rmmod is no
> longer an appropriate default policy on unplug, even though the
> module "refcount" is still zero, since the user could still try
> access the other device.  (Maybe they were plugging in devices
> until they found the one with the data they were after, and just
> hadn't looked at that the other one yet.)

Hmmm, interesting problem.  Perhaps your idea of having drivers hold a
refcount for every device they control makes sense in this case, but
as you point out, it's a significant departure from current policy.

With "rmmod -f" it's not quite reboot time, though.

Anyway, I don't think this is a battle I want to fight 8)

Cheers,
Rusty.
--
  Anyone who quotes me in their sig is an idiot. -- Rusty Russell.

Re: 2.5.47bk2 + current modutils == broken hotplug

[Gerd Knorr]

>  The question is whether to force an /sbin/hotplug change to use the
>  module alias mechanism, or generate the modules.*map files at "make
>  modules_install" time to avoid breakage.  I'm leaning towards #2, but
>  I haven't written it yet (should be simple).

Doing that at modules_install time doesn't work for external drivers
(which are _not_ in the kernel tree) ...

  Gerd

-- 
You can't please everybody.  And usually if you _try_ to please
everybody, the end result is one big mess.
				-- Linus Torvalds, 2002-04-20