Udev rule $attr substitution

Udev rule $attr substitution

[Josua Dietze]

Hi, everyone!

I'm scratching my head over this:

Rule line:
KERNEL="ttyUSB*" RUN+="myprog %p %s{idVendor} %s{idProduct}"

%p expands to something like:
/devices/pci0000:00/0000:00:1d.7/usb1/1-5/1-5:1.2/ttyUSB2/tty/ttyUSB2

But the %s (or $attr) format string will not be substituted with anything when 
using udev version 157. The same rule works fine with version 125.

When doing the attribute walk with "udevadm info", the attributes are of course 
found in the parent chain.

Did I miss something?

Re: Udev rule $attr substitution

[Josua Dietze]

Never mind, I figured it out.

It was all a problem of not-quite-accurate man pages.

I found the man page (well, xml file) in the git tree and just added an ATTRS 
match to the top level USB device.

This worked:
KERNEL="ttyUSB*", ATTRS{bNumConfigurations}="*", RUN+="myprog %p %s{idVendor} 
%s{idProduct}"

Sorry for the noise, thanks anyway.

But I might add that there is certainly some documentation lacking on this one, 
practially everything I found was outdated or inaccurate ...


Josua Dietze

Re: Udev rule $attr substitution

[Martin Pitt]

Hello Josua,

Josua Dietze [2010-12-21 21:25 +0100]:
> I found the man page (well, xml file) in the git tree and just added
> an ATTRS match to the top level USB device.
> 
> This worked:
> KERNEL="ttyUSB*", ATTRS{bNumConfigurations}="*", RUN+="myprog %p
> %s{idVendor} %s{idProduct}"

Right, you need to "select" the parent device of which you need the
id* attribute.

> But I might add that there is certainly some documentation lacking
> on this one, practially everything I found was outdated or
> inaccurate ...

This is indeed a common trap, so some time ago I tried to point this
out more clearly in the manpage:

      $attr{file}, %s{file}
           The value of a sysfs attribute found at the device, where all keys
           of the rule have matched. If the matching device does not have such
           an attribute, and a previous KERNELS, SUBSYSTEMS, DRIVERS, or ATTRS
           test selected a parent device, use the attribute from that parent
           device.

This tries to point out that this won't match attributes from any
parent device. Do you think this paragraph is unclear? If so, do you
have a suggestion how to improve it? Or did you not see it in the
first place?

Thank you,

Martin
-- 
Martin Pitt                        | http://www.piware.de
Ubuntu Developer (www.ubuntu.com)  | Debian Developer  (www.debian.org)

Re: Udev rule $attr substitution

[Josua Dietze]

Am 22.12.2010 09:51, schrieb Martin Pitt:
>> But I might add that there is certainly some documentation lacking
>> on this one, practially everything I found was outdated or
>> inaccurate ...
>
> This is indeed a common trap, so some time ago I tried to point this
> out more clearly in the manpage:
>
>        $attr{file}, %s{file}
>             The value of a sysfs attribute found at the device, where all keys
>             of the rule have matched. If the matching device does not have such
>             an attribute, and a previous KERNELS, SUBSYSTEMS, DRIVERS, or ATTRS
>             test selected a parent device, use the attribute from that parent
>             device.
>
> This tries to point out that this won't match attributes from any
> parent device. Do you think this paragraph is unclear? If so, do you
> have a suggestion how to improve it? Or did you not see it in the
> first place?

The entry in the current man page is fine.

I was broadly referring to the documentation floating around in the 
Web, examples, howtos and forum discussions. Nothing of your 
responsibility, really.

What's a bit unfortunate though is the discrepancy between man pages 
and functionality of versions before the man page correction. 
OpenSUSE 11.3 ships with v. 157 which claims to do the upward chain 
search for $attr but doesn't.

Maybe an "official" udev page consisting of the current man page and 
two or three additional notes regarding changes in previously 
available features would help. Or does it exist and I missed it?

Just my 2c,

Josua Dietze

Re: Udev rule $attr substitution

[Martin Pitt]

Hello Josua,

Josua Dietze [2010-12-22 12:42 +0100]:
> What's a bit unfortunate though is the discrepancy between man pages
> and functionality of versions before the man page correction.

That's right, there was a time when the manpage was still wrong. The
manpage was fixed in August:

  http://git.kernel.org/?p=linux/hotplug/udev.git;a=commitdiff;hƒ184d008ba2

> Maybe an "official" udev page consisting of the current man page and
> two or three additional notes regarding changes in previously
> available features would help. Or does it exist and I missed it?

The one I quoted from is the official manpage, as it is released
upstream in the last few versions (>= 162).

Martin
-- 
Martin Pitt                        | http://www.piware.de
Ubuntu Developer (www.ubuntu.com)  | Debian Developer  (www.debian.org)

Re: Udev rule $attr substitution

[Josua Dietze]

Am 22.12.2010 16:58, schrieb Martin Pitt:

> Josua Dietze [2010-12-22 12:42 +0100]:
>> Maybe an "official" udev page consisting of the current man page and
>> two or three additional notes regarding changes in previously
>> available features would help. Or does it exist and I missed it?
>
> The one I quoted from is the official manpage, as it is released
> upstream in the last few versions (>= 162).


I was thinking of something that would come up if you google for "udev man page" 
or "udev home"; this will hardly work for a XML file in a git tree ...

But it's no big deal either; I mean, I found it eventually, right? Those who 
really care will arrive there sooner or later.

Thanks for your time!

Josua Dietze

Re: Udev rule $attr substitution

[Kay Sievers]

On Wed, Dec 22, 2010 at 18:40, Josua Dietze <digidietze@draisberghof.de> wrote:
> Am 22.12.2010 16:58, schrieb Martin Pitt:
>
>> Josua Dietze [2010-12-22 12:42 +0100]:
>>>
>>> Maybe an "official" udev page consisting of the current man page and
>>> two or three additional notes regarding changes in previously
>>> available features would help. Or does it exist and I missed it?
>>
>> The one I quoted from is the official manpage, as it is released
>> upstream in the last few versions (>= 162).
>
>
> I was thinking of something that would come up if you google for "udev man
> page" or "udev home"; this will hardly work for a XML file in a git tree ...
>
> But it's no big deal either; I mean, I found it eventually, right? Those who
> really care will arrive there sooner or later.
>
> Thanks for your time!

We sync (make doc-sync in the tree) the generated html from the libs
the git tree to kernel.org for libudev and gudev:
  http://www.kernel.org/pub/linux/utils/kernel/hotplug/libudev/
  http://www.kernel.org/pub/linux/utils/kernel/hotplug/gudev/
 Should be easy to let xmlto create html pages for theman pages and
sync them to:
  http://www.kernel.org/pub/linux/utils/kernel/hotplug/udev/
 at the same time.

Kay

Re: Udev rule $attr substitution

[Kay Sievers]

On Wed, Dec 22, 2010 at 18:46, Kay Sievers <kay.sievers@vrfy.org> wrote:
> On Wed, Dec 22, 2010 at 18:40, Josua Dietze <digidietze@draisberghof.de> wrote:
>> Am 22.12.2010 16:58, schrieb Martin Pitt:
>>
>>> Josua Dietze [2010-12-22 12:42 +0100]:
>>>>
>>>> Maybe an "official" udev page consisting of the current man page and
>>>> two or three additional notes regarding changes in previously
>>>> available features would help. Or does it exist and I missed it?
>>>
>>> The one I quoted from is the official manpage, as it is released
>>> upstream in the last few versions (>= 162).
>>
>>
>> I was thinking of something that would come up if you google for "udev man
>> page" or "udev home"; this will hardly work for a XML file in a git tree ...
>>
>> But it's no big deal either; I mean, I found it eventually, right? Those who
>> really care will arrive there sooner or later.
>>
>> Thanks for your time!
>
> We sync (make doc-sync in the tree) the generated html from the libs
> the git tree to kernel.org for libudev and gudev:
>  http://www.kernel.org/pub/linux/utils/kernel/hotplug/libudev/
>  http://www.kernel.org/pub/linux/utils/kernel/hotplug/gudev/
>  Should be easy to let xmlto create html pages for theman pages and
> sync them to:
>  http://www.kernel.org/pub/linux/utils/kernel/hotplug/udev/
>  at the same time.

It's here now:
  http://www.kernel.org/pub/linux/utils/kernel/hotplug/udev/

Cheers,
Kay