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| author | Lukas Prediger | 2021-09-14 00:09:42 +0100 |
|---|---|---|
| committer | Jens Axboe | 2021-09-14 20:05:26 -0600 |
| commit | 67f1e027c27054e641584655020a417eaac9cb3a (patch) | |
| tree | cd436e8c697009cc6def17e4b77cd28503029ac3 /Documentation/cdrom | |
| parent | 316346243be6df12799c0b64b788e06bad97c30b (diff) | |
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.rst | 11 |
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_. |