submount?

[David Zeuthen]

On Mon, 2004-05-31 at 21:30, Alan Cox wrote:
> > Wouldn't it suffice with just an option to mount(1), e.g. have as few
> > changes to how this impact user space as possible. I mean, at the end of
> > the day, isn't this just about the kernel locking/unlocking the drive
> > (same for e.g. USB storage) only when there is I/O?
> 
> To do it properly you need a bit more because users may change CD-ROMs and you
> probably want to do "Please insert 'Install Disk 2'" type dialogs. 
> 
> Internally the kernel really doesn't deal with disks going away when they are
> wanted. Volumagic can cope with
> 
> 	cd /mnt/cdrom
> 	eject
> 	insert new cd
> 	ls
> 
> and also with requests when the disk is removed - not all file systems handle
> media vanishing as a routine thing.
> 

In my, possibly uninformed, opinion it would be nicest if optical discs
just appeared to the user like the other block devices out there e.g.

 /sys/block/hdc
 /sys/block/hdc/hdc1

Then your change notification would just be a hotplug event. Further,
for a mixed CD-ROM disc you would also have

 /sys/block/hdc/hdc2 

so you can access the data and audio parts simultaneously. This works on
Mac OS X, though the drive makes a lot of noise. I'm not sure how to
achieve this on Linux.

David