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drivers/cdrom: improved ioctl for media change detection

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The current implementation of the CDROM_MEDIA_CHANGED ioctl relies on
global state, meaning that only one process can detect a disc change
while the ioctl call will return 0 for other calling processes afterwards
(see bug 213267).

This introduces a new cdrom ioctl, CDROM_TIMED_MEDIA_CHANGE, that
works by maintaining a timestamp of the last detected disc change instead
of a boolean flag: Processes calling this ioctl command can provide
a timestamp of the last disc change known to them and receive
an indication whether the disc was changed since then and the updated
timestamp.

I considered fixing the buggy behavior in the original
CDROM_MEDIA_CHANGED ioctl but that would require maintaining state
for each calling process in the kernel, which seems like a worse
solution than introducing this new ioctl.

Signed-off-by: Lukas Prediger <lumip@lumip.de>
Link: https://lore.kernel.org/all/20210912191207.74449-1-lumip@lumip.de
Signed-off-by: Phillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/r/20210913230942.1188-1-phil@philpotter.co.uk
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Lukas Prediger
2021-09-14 00:09:42 +01:00
committed by Jens Axboe
parent 316346243b
commit 67f1e027c2
5 changed files with 89 additions and 4 deletions
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3
Documentation/userspace-api/ioctl/cdrom.rst
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@@ -54,6 +54,9 @@ are as follows:
CDROM_SELECT_SPEED Set the CD-ROM speed
CDROM_SELECT_DISC Select disc (for juke-boxes)
CDROM_MEDIA_CHANGED Check is media changed
CDROM_TIMED_MEDIA_CHANGE Check if media changed
since given time
(struct cdrom_timed_media_change_info)
CDROM_DRIVE_STATUS Get tray position, etc.
CDROM_DISC_STATUS Get disc type, etc.
CDROM_CHANGER_NSLOTS Get number of slots