Re: [RFC] cdrom weirdness

From: Jens Axboe
Date: Thu Dec 04 2008 - 08:09:15 EST

On Thu, Dec 04 2008, Al Viro wrote:
> 1) CDROM_LOCKDOOR sets a global variable (keeplocked) that affects all
> cdroms. Intentional?

It's always been so, predates me. Pretty ugly, I don't think anyone
would mind if that was changed to be per-device when the ioctl is ussed

> 2) cdrom_dvd_rw_close_write() call can be delayed indefinitely by keeping
> an ioctl-only (opened with O_NDELAY) descriptor.

Yep, not sure what you want me to say here...

> 3) open cdrom for data, have the door locked, keep fd opened.
> open it again for write, have the open fail and cleanup in cdrom_open()
> will happily unlock the door for you. I'd change that to "lock if we
> had no lockers, unlock on failure exit if we did lock", but there's
> an interesting comment:
> /* Something failed. Try to unlock the drive, because some drivers
> (notably ide-cd) lock the drive after every command.
> ...
> What the hell is that about? It's not "some drivers", AFAICT - it's
> been done explicitly in open_for_data(). Or is there something
> really driver-specific in it?
> 4) while we are at it, if you clear lockdoor via sysctl while something has
> cdrom opened - no unlock on close for you.
> 5) autoeject happens on the last close *IF* the last file happens to be
> opened for data. IOW, if some crap has opened it ioctl-only and kept
> that opened after everyone else has closed - no autoeject for you.

Most of the above are long known issues with not counting
write/non-write/ioctls opens, since it was tricky/impossible to do
because of fcntl().

> 6) /*
> * flush cache on last write release
> */
> if (CDROM_CAN(CDC_RAM) && !cdi->use_count && cdi->for_data)
> cdrom_close_write(cdi);
> is interesting, seeing that nothing has ever touched ->for_data, for
> values of "ever" including "since the code in question had been merged
> into the tree"...

Hmm weird, you are right. The member was added in 2.6.2, but never used
except here. I guess this just needs to use opened_for_data.

Jens Axboe

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