linux-kernel - [RFC] cdrom weirdness

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Message-ID: <20081204041450.GH28946@ZenIV.linux.org.uk>
Date:	Thu, 4 Dec 2008 04:14:50 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	axboe@...nel.dk
Cc:	linux-kernel@...r.kernel.org
Subject: [RFC] cdrom weirdness

1) CDROM_LOCKDOOR sets a global variable (keeplocked) that affects all
cdroms.  Intentional?

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

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.

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"...
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