Hotplug-- who notifies whom of what?

Hotplug-- who notifies whom of what?

[Bryan W. Headley]

Greg,

Regards to Aiptek USB tablets...

I'm trying to figure out a strategy for hotplugging.

1) The tablet is mapped to the input device system.
    a) Because the order in which drivers complete loading/registering
       is not deterministic (e.g., mouse driver spawns thread), I do not
       know with certainty that the tablet will always be mapped to
       /dev/input/event27. So, configuration files of certain (XFree)
       applications that require that the path be known and static enough
       to put in a text file.
    b) No problem. So I whip up a startup process that finds the tablet
       and creates a softlink that XF86Config-4 can refer to. That is
       relying on the sysvinit system, and is wrong insofar as it knows
       there's a tablet owned by the user (I'm thinking of RH, Mandrake,
       et al, quality scripts, here. Not little one-liners we all write.)

2) In case of a hotplug event, e.g., the tablet being disconnected, I
    really should get rid of the softlink...
    a) But is that the domain of a script in hotplug?

3) In case of hotplug-connect, I should re-create the softlink.
    a) Again, in the hotplug domain? I ask because I have an rc script
       that does the same thing on boot-up, and I'd rather not have
       things cross-referenced between two packages.
    b) Plus, what I do to find the aiptek tablet COULD BE scriptable on
       2.6, would be hard to script on 2.4. Anyway, it's not a script
       now, it makes ioctl calls.

4) Moving upstream... X needs to be notified that device 'x', that it's
    using for input, has been plugged/unplugged. No facility for that,
    except in my xf86aiptek device driver for X, which DOES have a
    bidirectional communications channel, which could have a "Unwind
    driver" API call
    a) Right now, the only thing that knows my API is my user-friendly
       front-end. It's not something you'd run as a daemon...
    b) But a subset of it certainly could. Question is, what does it
       listen for? Hotplug messages forwarded off of dbus? Does it
       monitor Hal? Is it really something that's fired off directly
       by hotplug? Or owned by hotplug?

5) Does udev fit into this conversation anywhere? It can be hotplug,
    dbus, or hal-aware, or do it's thing by itself...

Since I don't know, but plan to read up on the this stuff, I just wanted
to ask your opinions up-front. Certainly, there's a question as to 
whether hotplug wants to require the successful installation of hal, 
dbus. Or for that matter, adjuncts like discover, kudzu...

It's a two-pronged question: what to do now, and what directions to plan 
for the community to move towards.

-- 
____               .:.                 ____
Bryan W. Headley - bwheadley@earthlink.net



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Re: Hotplug-- who notifies whom of what?

[Greg KH]

On Mon, Feb 16, 2004 at 06:54:16PM -0600, Bryan W. Headley wrote:
> Greg,
> 
> Regards to Aiptek USB tablets...
> 
> I'm trying to figure out a strategy for hotplugging.
> 
> 1) The tablet is mapped to the input device system.
>    a) Because the order in which drivers complete loading/registering
>       is not deterministic (e.g., mouse driver spawns thread), I do not
>       know with certainty that the tablet will always be mapped to
>       /dev/input/event27. So, configuration files of certain (XFree)
>       applications that require that the path be known and static enough
>       to put in a text file.

Use udev to always create your "/dev/input/tablet_mine_all_mine" node so
that XFree does not have to be reconfigured all the time.

>    b) No problem. So I whip up a startup process that finds the tablet
>       and creates a softlink that XF86Config-4 can refer to. That is
>       relying on the sysvinit system, and is wrong insofar as it knows
>       there's a tablet owned by the user (I'm thinking of RH, Mandrake,
>       et al, quality scripts, here. Not little one-liners we all write.)

Sure, create a symlink in udev instead.  It can do that just fine if you
don't want to use a "real" node.

> 2) In case of a hotplug event, e.g., the tablet being disconnected, I
>    really should get rid of the softlink...
>    a) But is that the domain of a script in hotplug?

Nope, that's udev's job.

> 3) In case of hotplug-connect, I should re-create the softlink.

udev does that for you just fine.

>    a) Again, in the hotplug domain? I ask because I have an rc script
>       that does the same thing on boot-up, and I'd rather not have
>       things cross-referenced between two packages.
>    b) Plus, what I do to find the aiptek tablet COULD BE scriptable on
>       2.6, would be hard to script on 2.4. Anyway, it's not a script
>       now, it makes ioctl calls.
> 
> 4) Moving upstream... X needs to be notified that device 'x', that it's
>    using for input, has been plugged/unplugged. No facility for that,
>    except in my xf86aiptek device driver for X, which DOES have a
>    bidirectional communications channel, which could have a "Unwind
>    driver" API call
>    a) Right now, the only thing that knows my API is my user-friendly
>       front-end. It's not something you'd run as a daemon...
>    b) But a subset of it certainly could. Question is, what does it
>       listen for? Hotplug messages forwarded off of dbus? Does it
>       monitor Hal? Is it really something that's fired off directly
>       by hotplug? Or owned by hotplug?

How about listening to dbus messages?  That is the way that both GNOME
and KDE are moving to using.

> 5) Does udev fit into this conversation anywhere? It can be hotplug,
>    dbus, or hal-aware, or do it's thing by itself...

Yes it does, see above.

Hope this helps,

greg k-h


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Re: Hotplug-- who notifies whom of what?

[Greg KH]

On Tue, Feb 17, 2004 at 09:34:30AM -0600, Bryan W. Headley wrote:
> Greg KH wrote:
> >On Mon, Feb 16, 2004 at 06:54:16PM -0600, Bryan W. Headley wrote:
> >
> >>Greg,
> >>
> >>Regards to Aiptek USB tablets...
> >>
> >>I'm trying to figure out a strategy for hotplugging.
> >>
> >>1) The tablet is mapped to the input device system.
> >>  a) Because the order in which drivers complete loading/registering
> >>     is not deterministic (e.g., mouse driver spawns thread), I do not
> >>     know with certainty that the tablet will always be mapped to
> >>     /dev/input/event27. So, configuration files of certain (XFree)
> >>     applications that require that the path be known and static enough
> >>     to put in a text file.
> >
> >
> >Use udev to always create your "/dev/input/tablet_mine_all_mine" node so
> >that XFree does not have to be reconfigured all the time.
> 
> What do I do in 2.4-land? The silliness with hotplug scripts, .rc 
> scripts, etc.?

I don't really know, sorry.  Luckily I'm not running 2.4 on any of my
machines :)

Anyone else have an idea?

thanks,

greg k-h


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