Re: Reattach/redetect allways connected umass device - is it possible ?

On Tue, Mar 29, 2005 at 12:52:00PM +0200, Stijn Hoop wrote:
> On Tue, Mar 29, 2005 at 08:43:47PM +1000, Peter Jeremy wrote:
> > On Tue, 2005-Mar-29 10:16:05 +0200, Stijn Hoop wrote:
> > > From a desktop user experience point of view, it is rather nice to get
> > > a notification if and when removable media disappears, without
> > > continously polling said media.
> > 
> > There's no reason why the kernel couldn't regularly poll removable media
> > as long as it didn't interfere with normal operation of the device or
> > intrude upon the user (who remembers Amiga FDD's ticking?).
> 
> Powersaving reasons (as has been stated in this thread already, I
> believe) come to mind. Or, in some cases, physical wear & tear on the
> hardware -- although I believe it's not the case for regular USB flash
> drives, I can imagine an implementation that needs to access the
> physical media in order to determine status (cardreaders?).

Wear shouldn't be a problem.
All recent media types have mechanism for that.

> But as Poul-Henning said, it's up to the drivers themselves to resort
> to polling if needed.

Yes - and the most interesting these days is the da driver.

> > > This statement intentionally ignores
> > > the question of how to get such an event through the kernel to
> > > userspace.
> > 
> > I don't believe this is a problem.  For a command line interface, you
> > run "ls" and get a snapshot of the directory contents - you don't expect
> > the output from an old "ls" to magically update itself when a file is
> > deleted, you re-run "ls".  GUI file browsers are more of a problem but
> > as long as the browser doesn't cache the results from one invocation to
> > another, this wouldn't seem to be a problem.
> 
> I was not thinking of contents exactly; more of the desktop user
> experience where, by inserting an USB drive, an icon appears on the
> desktop. That icon should be removed when the drive is removed again.
> Other similar usecases abound.

But since you are talking about drive removal there shouldn't be a real
problem.
OK - GEOM and CAM could issue newbus notifications, but I think that's
already on someones todo list.
So far you get an umass attachment and easily process the rest.

> > In any case, the majority of the computer users seem quite happy with
> > a user interface that, upon ejecting a removable medium and inserting
> > a different medium, will happily display the union of the contents of
> > the old and new media.
> 
> I might be misreading the sarcasm here, but I for one am not happy
> with the mixed contents. I'm already a bit weary of using removable
> media with FreeBSD because I'm unsure what works and what does not.
> This is a situation I would like to remedy.

Everything works fine as long as you trigger a GEOM rescan after media
exchange.
drive exchange doesn't need any special handling.

-- 
B.Walter                   BWCT                http://www.bwct.de
bernd_at_bwct.de                                  info_at_bwct.de