Re: Questions on CDROM support

Jens Axboe (axboe@image.dk)
Sun, 10 Oct 1999 19:41:45 +0200

On Sat, Oct 09 1999, Anthony Barbachan wrote:
> This is what I'd like to do. I'd like to modify the EIDE and/or SCSI
> CDROM driver(s) to automatically mount a CD when it is inserted and unmount
> and eject it when the eject button is pressed (with possibly a flag to
> indicate unmount/eject only if no files are open on the CDROM or to delay
> the umount/eject until after all files close on the CDROM). Unfortunately
> the current need to mount/unmount the CDROM (floppy to, but I think little
> that can be done about that one) is nowhere near user freindly. The
> automounter doesn't really seam to suit this purpose for a few reasons. If
> some process happens to be in the CD's mount directory or any decending
> directories the CD is unejectable due to it being considered to be in use.
> The delay before unmounting the CD thus allowing it ejection raises the very
> real possibility of some quickly frustrated user(s) starting to rapidly
> press the eject button, bang on it, if not worse; people are used to the
> CDROM's behavior under DOS/Windows. Besides which I think mounting once on
> insertion and unmounting/ejecting when the eject button is pressed is a more
> efficient and elegant solution. I don't think mounting a CD, at most
> almost, on insertion should be a problem since at a minimum that could be
> done by polling though I think polling is ugly. But the eject button may be
> a different story. So I basically have two questions mostly related to
> SCSI/EIDE CDROMs though knowing about the others would be useful as well:

For far most drives you have to resort to polling, as the drive
cannot report event like that asynchronously (spec says that
SCSI drives can do this, but I haven't seen any that does). So
basically this could be done inside the drive or from a user
space utility and inform automount of when to mount the drive.
Polling from inside the driver is just not going to happen,
for just the reasons you state - ugly.

> Do SCSI or EIDE CDROMs notify the host enviroment in any way that a CD was
> inserted or that its status has changed either directly or indirectly?

There are several ways to do it. The newest (as per MMC and Mt Fuji)
is to use GET_EVENT_STATUS with either synch or async notification.
The former requires polling for events while the latter can inform
the driver when a certain event has taken place - not just media
events, but things like power management, etc. This ties in with
what I wrote above - asynch status _is_ possible, but since no
drives implement it...

> Do SCSI or EIDE CDROMs notify the host enviroment in any way that the eject
> button has been pressed or that its status has changed either directly or
> indirectly? If not, could the pressing of the eject button be monitored
> through some sort of polling?

Same as above. Your best choice is probably to poll with
CDROM_MEDIA_CHANGED and use that information, although that
can't tell you about eject attempts.

-- 
*  Jens Axboe <axboe@image.dk>
*  Linux CD-ROM Maintainer
*  http://www.kernel.dk


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