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

Jens Axboe
2004-01-07T09:50:42Z

On Wed, Jan 07 2004, Olaf Hering wrote:
> On Sat, Jan 03, Jens Axboe wrote:
>
> > On Sat, Jan 03 2004, Andrey Borzenkov wrote:
> > > > Is there really no way to get a media change notification from ZIP or
> > > > JAZ drives?
> > >
> > > If anyone knows please tell me - I will put it into supermount ...
> > >
> > > AFAIK in case of SCSI this is impossible simply by virtue of protocol - SCSI
> > > device is not initiator. So you need something to poll device for status.
> > > That is usually done on device open except in this case you can't open
> > > because you do not yet have handle.
> >
> > You could queue a media notification request for long periods of time,
> > being completed by the drive when a media change happens. At least mmc
> > allows for this, doubt anyone has ever done it.
> >
> > So yeah, poll...
>
> Poll how? "kmediachangethread"? Or polling in userland? The latter would
> (probably) lead to endless IO errors. Not very good.

No need to put it in the kernel, user space fits the bil nicely. I don't
see how this would lead to IO errors?

> If I understand the Darwin sources correctly, a polling is used. But I
> havent looked hard how they do it.

It's the only way to do it.

--
Jens Axboe