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authorLukas Prediger <lumip@lumip.de>2021-09-14 02:09:42 +0300
committerJens Axboe <axboe@kernel.dk>2021-09-15 05:05:26 +0300
commit67f1e027c27054e641584655020a417eaac9cb3a (patch)
treecd436e8c697009cc6def17e4b77cd28503029ac3 /Documentation/cdrom
parent316346243be6df12799c0b64b788e06bad97c30b (diff)
downloadlinux-67f1e027c27054e641584655020a417eaac9cb3a.tar.xz
drivers/cdrom: improved ioctl for media change detection
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>
Diffstat (limited to 'Documentation/cdrom')
-rw-r--r--Documentation/cdrom/cdrom-standard.rst11
1 files changed, 11 insertions, 0 deletions
diff --git a/Documentation/cdrom/cdrom-standard.rst b/Documentation/cdrom/cdrom-standard.rst
index 5845960ca382..52ea7b6b2fe8 100644
--- a/Documentation/cdrom/cdrom-standard.rst
+++ b/Documentation/cdrom/cdrom-standard.rst
@@ -907,6 +907,17 @@ commands can be identified by the underscores in their names.
specifies the slot for which the information is given. The special
value *CDSL_CURRENT* requests that information about the currently
selected slot be returned.
+`CDROM_TIMED_MEDIA_CHANGE`
+ Checks whether the disc has been changed since a user supplied time
+ and returns the time of the last disc change.
+
+ *arg* is a pointer to a *cdrom_timed_media_change_info* struct.
+ *arg->last_media_change* may be set by calling code to signal
+ the timestamp of the last known media change (by the caller).
+ Upon successful return, this ioctl call will set
+ *arg->last_media_change* to the latest media change timestamp (in ms)
+ known by the kernel/driver and set *arg->has_changed* to 1 if
+ that timestamp is more recent than the timestamp set by the caller.
`CDROM_DRIVE_STATUS`
Returns the status of the drive by a call to
*drive_status()*. Return values are defined in cdrom_drive_status_.