Re: polling mechanism for media presence

On Mar 21, 2007, at 7:48 AM, Alan Stern wrote:

> On Tue, 20 Mar 2007, Allen Curtis wrote:
>
>>>>> I am sorry. HAL? Where do I get this daemon?
>>>>
>>>> It's part of the hal package, which is included in Fedora and
>>>> presumably
>>>> other distributions as well.  See
>>>>
>>>> 	http://www.freedesktop.org/Software/hal
>>>
>>> What would an embedded distro use though?  HAL takes up
>>> multi-megabytes.
>>> A swapless system, with say 32 MB total RAM, probably won't find that
>>> to be a usable solution ...
>>>
>>
>> Gee Dave,
>>
>> How did you know? That is exactly what we have, an embedded system 
>> with
>> 32MB of RAM and no swap!
>>
>> We created the unusual_device entry to launch a kernel thread to do
>> this polling. This solution does not "feel" right but I do not know
>> what else to do.
>
> Another approach is to do the polling in userspace rather than in the
> kernel.  You could write a daemon that would constantly probe all the
> removable SCSI disk drives.  I don't know of any existing standalone
> program to do that.
>

This is our current, inefficient method. We actually have a batch file 
which sits around in a polling loop trying to mount or unmount the 
device depending on the current state.

It does work but it isn't very efficient. We actually did it this way 
as a "quick fix". I guess we stumbled onto the right solution?

- Allen



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