Hotplug and udev - a question

Hotplug and udev - a question

[John Que]

Hello,

 I saw that in the last versions of udev, hotplug is deprecated.
Configuring of adding devices is done through udev rules.
Can anybody say in a few sentences why was this change done?
What are the advantages of conifguring with udev rules over
using hotplug ?

Best Regards,
John


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Re: Hotplug and udev - a question

[Chris Smith]

>>>>> "John" = John Que <qwejohn@gmail.com> writes:

    John> Hello, I saw that in the last versions of udev, hotplug is
    John> deprecated.  Configuring of adding devices is done through
    John> udev rules.  Can anybody say in a few sentences why was this
    John> change done?  What are the advantages of conifguring with
    John> udev rules over using hotplug ?

    John> Best Regards, John


John,
 Greg KH wrote an article that summarizes things nicely about a year ago:
 http://lwn.net/Articles/123932/
 Beating a drum from another post of mine that hasn't seen much
 response, I hope that the documentation for building a bootable
 kernel with all this udev goodness catches up.  It's rather
 mysterious at the moment.
Best,
Chris



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Re: Hotplug and udev - a question

[Greg KH]

On Fri, Mar 31, 2006 at 05:41:29AM -0500, Chris Smith wrote:
>  Beating a drum from another post of mine that hasn't seen much
>  response, I hope that the documentation for building a bootable
>  kernel with all this udev goodness catches up.  It's rather
>  mysterious at the moment.

Look at the initramfs building tool that debian uses for one example, or
the one that Gentoo has, or the one that SuSE uses.

That's three working examples that should help you figure out how to do
this for your system.

Hope this helps,

greg k-h


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Re: Hotplug and udev - a question

[John Que]

Hello,

Thanks for the link!
I read it carefully; all of it , except of the last 2
paragraphs, deal mainly with hotplug and improvements that
were made in hotplug-ng.

Now, to the last 2 paragrapghs:

>With the release of the 050 release of udev, if /sbin/udevsend is the kernel
>hotplug program (it can be changed by modifying the value of the
>/proc/sys/kernel/hotplug file), then it operates like the original
>/etc/hotplug.d multiplexer program as well as handling all of the udev device
>node generation. This ensures that the /etc/hotplug.d/ invocations
happen in the
>proper order, and in sequence for the same device. Gentoo Linux
already supports
>this mode of operation.

>However, not every user wants to use udev. Because of that, the hotplug-ng
>project is continuing, even if it seems like they are competing against each
>other in implementing the same functionality. As the same developers are doing
>the work in both programs, all users of Linux benefit with a faster module
>loading process, and further advancements in hotplug functionality.


What I don't get from here is what is exactly the advantage
of using udev solely over using udev with hotplug and what
is the exact reason that hotplug is deprecated.
Is it because there is some functionality which is duplicated
in udev and in hotplug ? or some other reason ?

Regards,
John


On 3/31/06, Chris Smith <smitty_one_each@bigfoot.com> wrote:
> >>>>> "John" = John Que <qwejohn@gmail.com> writes:
>
>     John> Hello, I saw that in the last versions of udev, hotplug is
>     John> deprecated.  Configuring of adding devices is done through
>     John> udev rules.  Can anybody say in a few sentences why was this
>     John> change done?  What are the advantages of conifguring with
>     John> udev rules over using hotplug ?
>
>     John> Best Regards, John
>
>
> John,
>  Greg KH wrote an article that summarizes things nicely about a year ago:
>  http://lwn.net/Articles/123932/
>  Beating a drum from another post of mine that hasn't seen much
>  response, I hope that the documentation for building a bootable
>  kernel with all this udev goodness catches up.  It's rather
>  mysterious at the moment.
> Best,
> Chris
>
>
>
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Re: Hotplug and udev - a question

[Chris Smith]

>>>>> "John" = John Que <qwejohn@gmail.com> writes:
    John> What I don't get from here is what is exactly the advantage
    John> of using udev solely over using udev with hotplug and what
    John> is the exact reason that hotplug is deprecated.  Is it
    John> because there is some functionality which is duplicated in
    John> udev and in hotplug ? or some other reason ?

Take this with a grain of salt, but my understanding is that, from a
kernel perspective, the udev way is smaller, simpler, and more
flexible.
Best,
Chris



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Re: Hotplug and udev - a question

[Greg KH]

On Sun, Apr 02, 2006 at 05:04:30PM +0300, John Que wrote:
> Hello,
> 
> Thanks for the link!
> I read it carefully; all of it , except of the last 2
> paragraphs, deal mainly with hotplug and improvements that
> were made in hotplug-ng.
> 
> Now, to the last 2 paragrapghs:
> 
> >With the release of the 050 release of udev, if /sbin/udevsend is the kernel
> >hotplug program (it can be changed by modifying the value of the
> >/proc/sys/kernel/hotplug file), then it operates like the original
> >/etc/hotplug.d multiplexer program as well as handling all of the udev device
> >node generation. This ensures that the /etc/hotplug.d/ invocations
> happen in the
> >proper order, and in sequence for the same device. Gentoo Linux
> already supports
> >this mode of operation.
> 
> >However, not every user wants to use udev. Because of that, the hotplug-ng
> >project is continuing, even if it seems like they are competing against each
> >other in implementing the same functionality. As the same developers are doing
> >the work in both programs, all users of Linux benefit with a faster module
> >loading process, and further advancements in hotplug functionality.
> 
> 
> What I don't get from here is what is exactly the advantage
> of using udev solely over using udev with hotplug and what
> is the exact reason that hotplug is deprecated.
> Is it because there is some functionality which is duplicated
> in udev and in hotplug ? or some other reason ?

Turns out you can do everything that hotplug did with just about 1 udev
rule.  So that makes the hotplug package obsolete.

Now the hotplug package did do a few other odd things (firmware loading,
etc.) that has been moved over to udev with external scripts for those
systems that only use udev instead of hotplug.  So if you do this,
please be aware of this.

thanks,

greg k-h


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Re: Hotplug and udev - a question

[Anssi Saari]

On Sun, Apr 02, 2006 at 05:04:30PM +0300, John Que wrote:
 
> What I don't get from here is what is exactly the advantage
> of using udev solely over using udev with hotplug and what
> is the exact reason that hotplug is deprecated.
> Is it because there is some functionality which is duplicated
> in udev and in hotplug ? or some other reason ?

From a user's perspective, I'd say the advantage of getting rid of stinky
hotplug is speed. On my desktop Debian Sarge box hotplug scripts grind
away incredibly long stretching boot time well into annoying lenght. OTOH,
in my Arch laptop the modules get loaded in a snap. Considering the
Arch machine is an old Thinkpad X20 with 600 MHz CPU, you can imagine
my pleasure when a recent Arch update did away with hotplug... 

Now that we are on the subject, has anyone dumped hotplug on their Debian
Sarge machine? I think I have all the parts I need already, udev, kernel
2.6.15, but I'm not sure what changes I'd have to make to get rid of
hotplug and load drivers in the udev way.


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Re: Hotplug and udev - a question

[juuso.alasuutari]

Quoting Anssi Saari <as@sci.fi>:

> From a user's perspective, I'd say the advantage of getting rid of stinky
> hotplug is speed. On my desktop Debian Sarge box hotplug scripts grind
> away incredibly long stretching boot time well into annoying lenght. OTOH,
> in my Arch laptop the modules get loaded in a snap. Considering the
> Arch machine is an old Thinkpad X20 with 600 MHz CPU, you can imagine
> my pleasure when a recent Arch update did away with hotplug...
>
> Now that we are on the subject, has anyone dumped hotplug on their Debian
> Sarge machine? I think I have all the parts I need already, udev, kernel
> 2.6.15, but I'm not sure what changes I'd have to make to get rid of
> hotplug and load drivers in the udev way.

I use Source Mage, but I believe rules for module loading are more or less
universal. Here's how I was able to rid my box of hotplug.


After all other lines, at the very end of my rules file, I have these:

# Load firmware
SUBSYSTEM="firmware", ACTION="add", RUN+="/lib/udev/firmware_helper"

# Autoload modules
SYSFS{modalias}="?*", ACTION="add", RUN+="/sbin/modprobe $env{MODALIAS}"

# Autoload modules that lack aliases but have them defined in
# /etc/modprobe.conf
SUBSYSTEM="pnp", ENV{MODALIAS}!="?*", RUN+="/bin/sh -c 'while read id; do
/sbin/modprobe pnp:d$$id; done < /sys$devpath/id'"


I also have certain module aliases set in /etc/modprobe.conf:

# These are needed by udev to autoload some modules
alias pnp:dPNP0510 irtty-sir
alias pnp:dPNP0511 irtty-sir
alias pnp:dPNP0700 floppy
alias pnp:dPNP0800 pcspkr
alias pnp:dPNP0b00 rtc
alias pnp:dPNP0303 atkbd
alias pnp:dPNP0f13 psmouse
alias pnp:dPNPb02f analog


Those edits should take care of module loading. Just make sure you remove any
previous firmware loading rules you might find in your present rules files.
The people on this list helped me earlier with this same issue, so in case I
missed or misrepresented something in this mail, check out this thread:
http://marc.theaimsgroup.com/?t\x114141804400005&r=1&w=2

Oh, and you might learn more by looking at the udev and modprobe configuration
of your Arch laptop.

Juuso Alasuutari

PS: If these rules work for you, please let me hear about it.

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