Re: removable media revalidation - udev vs. devfs or static /dev

Matt Mackall
2004-01-09T01:17:37Z

On Thu, Jan 08, 2004 at 07:28:47PM -0500, Robert Love wrote:
> On Wed, 2004-01-07 at 22:43, Linus Torvalds wrote:
>
> > Yes. We _could_ do that, by just making a "we noticed the disk change" be
> > a hotplug event. However, I'm loath to do that, because some devices
> > literally don't even have an easily read disk change signal, so what they
> > do is
>
> I like the idea of a hotplug event on media change (basically, a hotplug
> event for partitions). And, in fact, I am loath not to do it.
>
> The current direction with the kernel and udev is letting us move _away_
> from polling. Projects such as HAL are helping to finally integrate
> hardware management throughout the system. But HAL is going to be very
> confused by some of the alternative solutions for partitions: requiring
> that all of the partition device nodes preexist is going to really
> complicate things, and I really do not want to have to poll on all of
> them in order for HAL to have an idea of what partitions are valid.
>
> But I hear you loud and clear about dumb devices that cannot detect
> media change. They pose a problem.

If we have a hotplug media change event we can do:

if new device x appears:
x->device_nodes = all possible partition nodes
start_media_change_timer()
if media change on x:
x->device_nodes = current media partitions
clear_media_change_timer()
create_nodes(x)
if timeout: /* we didn't get media change so create all nodes */
create_nodes(x)

Then the dumb devices (which should be a small minority) just show up
with a harmless excess of partitions.

--
Matt Mackall : http://www.selenic.com : Linux development and consulting