udev and parallel port support

udev and parallel port support

[Jason Dravet]

Hello,

I opened bugzilla bug 145148
(https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id\x145148) at the
beginning of this year.  Udev was creating a bunch of unnecessary items in
/dev.  The parallel ports were mentioned specifically along with a large
number of ttyS and tty nodes.  When redhat responded to the bug I found out
that udev had to create the parallel port nodes itself using a rule because
the parallel port module was not loading at boot time.  I opened the bug to
get the parallel port module to load at boot time so udev could dynamically
create the nodes instead of creating 4 parallel ports when most people have
(use) one.  

I received an email asking me to try the new fedora core 4 kernel.  I have
installed it and it works fine for me.  The issue is udev is still creating
the parallel port statically instead of dynamically.  When will udev be able
to dynamically create the nodes for parallel ports?

Thank you for your time,

Jason

P.S.  Does anyone know why udev creates 76 ttyS* nodes and 65 tty nodes in
/dev?



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Re: udev and parallel port support

[Greg KH]

On Mon, Oct 03, 2005 at 12:24:24PM -0500, Jason Dravet wrote:
> Hello,
> 
> I opened bugzilla bug 145148
> (https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id\x145148) at the
> beginning of this year.  Udev was creating a bunch of unnecessary items in
> /dev.  The parallel ports were mentioned specifically along with a large
> number of ttyS and tty nodes.  When redhat responded to the bug I found out
> that udev had to create the parallel port nodes itself using a rule because
> the parallel port module was not loading at boot time.  I opened the bug to
> get the parallel port module to load at boot time so udev could dynamically
> create the nodes instead of creating 4 parallel ports when most people have
> (use) one.  
> 
> I received an email asking me to try the new fedora core 4 kernel.  I have
> installed it and it works fine for me.  The issue is udev is still creating
> the parallel port statically instead of dynamically.  When will udev be able
> to dynamically create the nodes for parallel ports?

It does so today just fine, the last time I looked.  It's a kernel
issue, not a udev issue.

How could udev be creating devices "statically"?  It's up to the kernel
to export what it has availble, and right now, it just exports them all.
Is that what bothers you?  If so, feel free to change the kernel code to
work better if you wish.

But again, it's a kernel issue, not a udev issue.

thanks,

greg k-h


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RE: udev and parallel port support

[Jason Dravet]

> -----Original Message-----
> From: Greg KH [mailto:greg@kroah.com]
> Sent: Tuesday, October 04, 2005 4:31 PM
> To: Jason Dravet
> Cc: linux-hotplug-devel@lists.sourceforge.net
> Subject: Re: udev and parallel port support
> 
> On Mon, Oct 03, 2005 at 12:24:24PM -0500, Jason Dravet wrote:
> > Hello,
> >
> > I opened bugzilla bug 145148
> > (https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id\x145148) at the
> > beginning of this year.  Udev was creating a bunch of unnecessary items
> in
> > /dev.  The parallel ports were mentioned specifically along with a large
> > number of ttyS and tty nodes.  When redhat responded to the bug I found
> out
> > that udev had to create the parallel port nodes itself using a rule
> because
> > the parallel port module was not loading at boot time.  I opened the bug
> to
> > get the parallel port module to load at boot time so udev could
> dynamically
> > create the nodes instead of creating 4 parallel ports when most people
> have
> > (use) one.
> >
> > I received an email asking me to try the new fedora core 4 kernel.  I
> have
> > installed it and it works fine for me.  The issue is udev is still
> creating
> > the parallel port statically instead of dynamically.  When will udev be
> able
> > to dynamically create the nodes for parallel ports?
> 
> It does so today just fine, the last time I looked.  It's a kernel
> issue, not a udev issue.
> 
> How could udev be creating devices "statically"?  It's up to the kernel
> to export what it has availble, and right now, it just exports them all.
> Is that what bothers you?  If so, feel free to change the kernel code to
> work better if you wish.
> 
> But again, it's a kernel issue, not a udev issue.
> 
> thanks,
> 
> greg k-h

I am sorry I did not make my self clear.  What I meant is that udev creates
the /dev/lp0, /dev/parport0, /dev/lp1, ..., /dev/parport3 nodes by looking
at /etc/udev/makedev.d/50-udev.nodes instead of actually detecting the
ports.  In the 50-udev.nodes file it says "These device have to be created
manually" and proceeds to list several items include lp0.  At least that is
what happens in version 0.58.  Does it make sense now?

Thanks,

Jason



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Re: udev and parallel port support

[Greg KH]

On Tue, Oct 04, 2005 at 04:48:43PM -0500, Jason Dravet wrote:
> 
> I am sorry I did not make my self clear.  What I meant is that udev creates
> the /dev/lp0, /dev/parport0, /dev/lp1, ..., /dev/parport3 nodes by looking
> at /etc/udev/makedev.d/50-udev.nodes instead of actually detecting the
> ports.  In the 50-udev.nodes file it says "These device have to be created
> manually" and proceeds to list several items include lp0.

That sounds like a redhat specific change to udev, please take it up
with them.

> At least that is what happens in version 0.58.  Does it make sense
> now?

There is no such thing as a udev release numbered 0.58, sorry :)

thanks,

greg k-h


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Re: udev and parallel port support

[Kay Sievers]

On Tue, Oct 04, 2005 at 04:48:43PM -0500, Jason Dravet wrote:
> > -----Original Message-----
> > From: Greg KH [mailto:greg@kroah.com]
> > Sent: Tuesday, October 04, 2005 4:31 PM
> > To: Jason Dravet
> > Cc: linux-hotplug-devel@lists.sourceforge.net
> > Subject: Re: udev and parallel port support
> > 
> > On Mon, Oct 03, 2005 at 12:24:24PM -0500, Jason Dravet wrote:
> > > Hello,
> > >
> > > I opened bugzilla bug 145148
> > > (https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id\x145148) at the
> > > beginning of this year.  Udev was creating a bunch of unnecessary items
> > in
> > > /dev.  The parallel ports were mentioned specifically along with a large
> > > number of ttyS and tty nodes.  When redhat responded to the bug I found
> > out
> > > that udev had to create the parallel port nodes itself using a rule
> > because
> > > the parallel port module was not loading at boot time.  I opened the bug
> > to
> > > get the parallel port module to load at boot time so udev could
> > dynamically
> > > create the nodes instead of creating 4 parallel ports when most people
> > have
> > > (use) one.
> > >
> > > I received an email asking me to try the new fedora core 4 kernel.  I
> > have
> > > installed it and it works fine for me.  The issue is udev is still
> > creating
> > > the parallel port statically instead of dynamically.  When will udev be
> > able
> > > to dynamically create the nodes for parallel ports?
> > 
> > It does so today just fine, the last time I looked.  It's a kernel
> > issue, not a udev issue.
> > 
> > How could udev be creating devices "statically"?  It's up to the kernel
> > to export what it has availble, and right now, it just exports them all.
> > Is that what bothers you?  If so, feel free to change the kernel code to
> > work better if you wish.
> > 
> > But again, it's a kernel issue, not a udev issue.
> > 
> > thanks,
> > 
> > greg k-h
> 
> I am sorry I did not make my self clear.  What I meant is that udev creates
> the /dev/lp0, /dev/parport0, /dev/lp1, ..., /dev/parport3 nodes by looking
> at /etc/udev/makedev.d/50-udev.nodes instead of actually detecting the
> ports.  In the 50-udev.nodes file it says "These device have to be created
> manually" and proceeds to list several items include lp0.  At least that is
> what happens in version 0.58.  Does it make sense now?

/etc/udev/makedev.d/ exists only on Red Hat. Every distro has it's own
way to create the "static" nodes.

Kay


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RE: udev and parallel port support

[Jason Dravet]

> -----Original Message-----
> From: Greg KH [mailto:greg@kroah.com]
> Sent: Tuesday, October 04, 2005 4:56 PM
> To: Jason Dravet
> Cc: linux-hotplug-devel@lists.sourceforge.net
> Subject: Re: udev and parallel port support
> 
> On Tue, Oct 04, 2005 at 04:48:43PM -0500, Jason Dravet wrote:
> >
> > I am sorry I did not make my self clear.  What I meant is that udev
> creates
> > the /dev/lp0, /dev/parport0, /dev/lp1, ..., /dev/parport3 nodes by
> looking
> > at /etc/udev/makedev.d/50-udev.nodes instead of actually detecting the
> > ports.  In the 50-udev.nodes file it says "These device have to be
> created
> > manually" and proceeds to list several items include lp0.
> 
> That sounds like a redhat specific change to udev, please take it up
> with them.
> 
> > At least that is what happens in version 0.58.  Does it make sense
> > now?
> 
> There is no such thing as a udev release numbered 0.58, sorry :)
> 
> thanks,
> 
> greg k-h

I will change the bug from kernel to udev on redhat's website.  If you don't
know about a 0.58 release of udev I am guessing that it is redhat's version.
I just updated my fedora core 4 to the development version of glibc and udev
(0.69) and the /etc/udev/makedev.d/50-udev-nodes file is still there.

So in short udev CAN dynamically create the lp and parport nodes.  Is that
correct? 

Thanks,

Jason



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RE: udev and parallel port support

[Jason Dravet]

> -----Original Message-----
> From: Kay Sievers [mailto:kay.sievers@vrfy.org]
> Sent: Tuesday, October 04, 2005 4:58 PM
> To: Jason Dravet
> Cc: 'Greg KH'; linux-hotplug-devel@lists.sourceforge.net
> Subject: Re: udev and parallel port support
> 
> On Tue, Oct 04, 2005 at 04:48:43PM -0500, Jason Dravet wrote:
> > > -----Original Message-----
> > > From: Greg KH [mailto:greg@kroah.com]
> > > Sent: Tuesday, October 04, 2005 4:31 PM
> > > To: Jason Dravet
> > > Cc: linux-hotplug-devel@lists.sourceforge.net
> > > Subject: Re: udev and parallel port support
> > >
> > > On Mon, Oct 03, 2005 at 12:24:24PM -0500, Jason Dravet wrote:
> > > > Hello,
> > > >
> > > > I opened bugzilla bug 145148
> > > > (https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id\x145148) at the
> > > > beginning of this year.  Udev was creating a bunch of unnecessary
> items
> > > in
> > > > /dev.  The parallel ports were mentioned specifically along with a
> large
> > > > number of ttyS and tty nodes.  When redhat responded to the bug I
> found
> > > out
> > > > that udev had to create the parallel port nodes itself using a rule
> > > because
> > > > the parallel port module was not loading at boot time.  I opened the
> bug
> > > to
> > > > get the parallel port module to load at boot time so udev could
> > > dynamically
> > > > create the nodes instead of creating 4 parallel ports when most
> people
> > > have
> > > > (use) one.
> > > >
> > > > I received an email asking me to try the new fedora core 4 kernel.
> I
> > > have
> > > > installed it and it works fine for me.  The issue is udev is still
> > > creating
> > > > the parallel port statically instead of dynamically.  When will udev
> be
> > > able
> > > > to dynamically create the nodes for parallel ports?
> > >
> > > It does so today just fine, the last time I looked.  It's a kernel
> > > issue, not a udev issue.
> > >
> > > How could udev be creating devices "statically"?  It's up to the
> kernel
> > > to export what it has availble, and right now, it just exports them
> all.
> > > Is that what bothers you?  If so, feel free to change the kernel code
> to
> > > work better if you wish.
> > >
> > > But again, it's a kernel issue, not a udev issue.
> > >
> > > thanks,
> > >
> > > greg k-h
> >
> > I am sorry I did not make my self clear.  What I meant is that udev
> creates
> > the /dev/lp0, /dev/parport0, /dev/lp1, ..., /dev/parport3 nodes by
> looking
> > at /etc/udev/makedev.d/50-udev.nodes instead of actually detecting the
> > ports.  In the 50-udev.nodes file it says "These device have to be
> created
> > manually" and proceeds to list several items include lp0.  At least that
> is
> > what happens in version 0.58.  Does it make sense now?
> 
> /etc/udev/makedev.d/ exists only on Red Hat. Every distro has it's own
> way to create the "static" nodes.
> 
> Kay

Thank you for the response.  I realize that some devices need static nodes,
but I am wondering why parallel ports fall into this category at least they
do according to redhat anyways?

Thanks,

Jason



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Re: udev and parallel port support

[Greg KH]

On Tue, Oct 04, 2005 at 05:12:24PM -0500, Jason Dravet wrote:
> 
> So in short udev CAN dynamically create the lp and parport nodes.  Is that
> correct? 

Yes.

thanks,

greg k-h


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Re: udev and parallel port support

['Kay Sievers']

On Tue, Oct 04, 2005 at 05:14:11PM -0500, Jason Dravet wrote:
> > -----Original Message-----
> > From: Kay Sievers [mailto:kay.sievers@vrfy.org]
> > Sent: Tuesday, October 04, 2005 4:58 PM
> > To: Jason Dravet
> > Cc: 'Greg KH'; linux-hotplug-devel@lists.sourceforge.net
> > Subject: Re: udev and parallel port support
> > 
> > On Tue, Oct 04, 2005 at 04:48:43PM -0500, Jason Dravet wrote:
> > > > -----Original Message-----
> > > > From: Greg KH [mailto:greg@kroah.com]
> > > > Sent: Tuesday, October 04, 2005 4:31 PM
> > > > To: Jason Dravet
> > > > Cc: linux-hotplug-devel@lists.sourceforge.net
> > > > Subject: Re: udev and parallel port support
> > > >
> > > > On Mon, Oct 03, 2005 at 12:24:24PM -0500, Jason Dravet wrote:
> > > > > Hello,
> > > > >
> > > > > I opened bugzilla bug 145148
> > > > > (https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id\x145148) at the
> > > > > beginning of this year.  Udev was creating a bunch of unnecessary
> > items
> > > > in
> > > > > /dev.  The parallel ports were mentioned specifically along with a
> > large
> > > > > number of ttyS and tty nodes.  When redhat responded to the bug I
> > found
> > > > out
> > > > > that udev had to create the parallel port nodes itself using a rule
> > > > because
> > > > > the parallel port module was not loading at boot time.  I opened the
> > bug
> > > > to
> > > > > get the parallel port module to load at boot time so udev could
> > > > dynamically
> > > > > create the nodes instead of creating 4 parallel ports when most
> > people
> > > > have
> > > > > (use) one.
> > > > >
> > > > > I received an email asking me to try the new fedora core 4 kernel.
> > I
> > > > have
> > > > > installed it and it works fine for me.  The issue is udev is still
> > > > creating
> > > > > the parallel port statically instead of dynamically.  When will udev
> > be
> > > > able
> > > > > to dynamically create the nodes for parallel ports?
> > > >
> > > > It does so today just fine, the last time I looked.  It's a kernel
> > > > issue, not a udev issue.
> > > >
> > > > How could udev be creating devices "statically"?  It's up to the
> > kernel
> > > > to export what it has availble, and right now, it just exports them
> > all.
> > > > Is that what bothers you?  If so, feel free to change the kernel code
> > to
> > > > work better if you wish.
> > > >
> > > > But again, it's a kernel issue, not a udev issue.
> > > >
> > > > thanks,
> > > >
> > > > greg k-h
> > >
> > > I am sorry I did not make my self clear.  What I meant is that udev
> > creates
> > > the /dev/lp0, /dev/parport0, /dev/lp1, ..., /dev/parport3 nodes by
> > looking
> > > at /etc/udev/makedev.d/50-udev.nodes instead of actually detecting the
> > > ports.  In the 50-udev.nodes file it says "These device have to be
> > created
> > > manually" and proceeds to list several items include lp0.  At least that
> > is
> > > what happens in version 0.58.  Does it make sense now?
> > 
> > /etc/udev/makedev.d/ exists only on Red Hat. Every distro has it's own
> > way to create the "static" nodes.

> Thank you for the response.  I realize that some devices need static nodes,
> but I am wondering why parallel ports fall into this category at least they
> do according to redhat anyways?

Sure, if you always load the module, there is no need to create the nodes.
In the past opening the node loaded the module, so with the switch to
udev it was just easier just to create the node. :)
Today it should be possible to "coldplug" the module load with the pnp id.

The "raw" parport is in:
  /sys/class/ppdev/parport0

The lp is in:
  /sys/class/printer/lp0

udev creates the nodes for both devices if the module is loaded.

Kay


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Re: udev and parallel port support

[Sergey Vlasov]

[-- Attachment #1: Type: text/plain, Size: 1037 bytes --]

On Tue, 4 Oct 2005 17:14:11 -0500 Jason Dravet wrote:

> Thank you for the response.  I realize that some devices need static nodes,
> but I am wondering why parallel ports fall into this category at least they
> do according to redhat anyways?

Actually, the lowlevel port driver (parport_pc, or maybe something
other like parport_serial) can in many cases be loaded automatically
(on most modern machines the presence of a legacy parallel port is
shown by PnP or ACPI).  Only old hardware which does not support any
form of PnP will require manual loading of parport_pc.

The real problem is that currently there is nothing which will trigger
loading of the highlevel driver (lp or ppdev).  With recent hardware
it is possible to find out what is connected to the parallel port
(look at /proc/sys/dev/parport/parport0/autoprobe), but this is often
unreliable.  So the easy way is to create static nodes for /dev/lp*
and /dev/parport*, and then a program which tries to use these devices
will trigger loading of the appropriate module.

[-- Attachment #2: Type: application/pgp-signature, Size: 189 bytes --]

RE: udev and parallel port support

[Jason Dravet]

> -----Original Message-----
> From: Sergey Vlasov [mailto:vsu@altlinux.ru]
> Sent: Wednesday, October 05, 2005 6:48 AM
> To: Jason Dravet
> Cc: 'Kay Sievers'; linux-hotplug-devel@lists.sourceforge.net
> Subject: Re: udev and parallel port support
> 
> On Tue, 4 Oct 2005 17:14:11 -0500 Jason Dravet wrote:
> 
> > Thank you for the response.  I realize that some devices need static
> nodes,
> > but I am wondering why parallel ports fall into this category at least
> they
> > do according to redhat anyways?
> 
> Actually, the lowlevel port driver (parport_pc, or maybe something
> other like parport_serial) can in many cases be loaded automatically
> (on most modern machines the presence of a legacy parallel port is
> shown by PnP or ACPI).  Only old hardware which does not support any
> form of PnP will require manual loading of parport_pc.
> 
> The real problem is that currently there is nothing which will trigger
> loading of the highlevel driver (lp or ppdev).  With recent hardware
> it is possible to find out what is connected to the parallel port
> (look at /proc/sys/dev/parport/parport0/autoprobe), but this is often
> unreliable.  So the easy way is to create static nodes for /dev/lp*
> and /dev/parport*, and then a program which tries to use these devices
> will trigger loading of the appropriate module.

Thank you to all of you who responded.  I learned a lot from your responses.
I think I now have an understanding of the issues involved.

Jason Dravet



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Re: udev and parallel port support

[Marco d'Itri]

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On Oct 05, Sergey Vlasov <vsu@altlinux.ru> wrote:

> The real problem is that currently there is nothing which will trigger
> loading of the highlevel driver (lp or ppdev).  With recent hardware
> it is possible to find out what is connected to the parallel port
> (look at /proc/sys/dev/parport/parport0/autoprobe), but this is often
> unreliable.
Can you tell us more about how autodetection would work?

(Anyway, I think that forcing to load both lp and ppdev with a modprobe
install rule would be much better than manually creating the devices.)

-- 
ciao,
Marco

[-- Attachment #2: Digital signature --]
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