Commit 67f1e027 authored by Lukas Prediger's avatar Lukas Prediger Committed by Jens Axboe
Browse files

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: default avatarLukas Prediger <lumip@lumip.de>
Link: https://lore.kernel.org/all/20210912191207.74449-1-lumip@lumip.de


Signed-off-by: default avatarPhillip Potter <phil@philpotter.co.uk>
Link: https://lore.kernel.org/r/20210913230942.1188-1-phil@philpotter.co.uk


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 31634624

Documentation/cdrom/cdrom-standard.rst

+11 −0
Original line number Diff line number Diff line
@@ -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_.

Documentation/userspace-api/ioctl/cdrom.rst

+3 −0
Original line number Diff line number Diff line
@@ -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

drivers/cdrom/cdrom.c

+55 −4
Original line number Diff line number Diff line
@@ -344,6 +344,12 @@ static void cdrom_sysctl_register(void); 


static LIST_HEAD(cdrom_list);



static void signal_media_change(struct cdrom_device_info *cdi)

{

	cdi->mc_flags = 0x3; /* set media changed bits, on both queues */

	cdi->last_media_change_ms = ktime_to_ms(ktime_get());

}



int cdrom_dummy_generic_packet(struct cdrom_device_info *cdi,

			       struct packet_command *cgc)

{
@@ -616,6 +622,7 @@ int register_cdrom(struct gendisk *disk, struct cdrom_device_info *cdi) 
	ENSURE(cdo, generic_packet, CDC_GENERIC_PACKET);

	cdi->mc_flags = 0;

	cdi->options = CDO_USE_FFLAGS;

	cdi->last_media_change_ms = ktime_to_ms(ktime_get());



	if (autoclose == 1 && CDROM_CAN(CDC_CLOSE_TRAY))

		cdi->options |= (int) CDO_AUTO_CLOSE;
@@ -1421,8 +1428,7 @@ static int cdrom_select_disc(struct cdrom_device_info *cdi, int slot) 
		cdi->ops->check_events(cdi, 0, slot);



	if (slot == CDSL_NONE) {

		/* set media changed bits, on both queues */

		cdi->mc_flags = 0x3;

		signal_media_change(cdi);

		return cdrom_load_unload(cdi, -1);

	}
@@ -1455,7 +1461,7 @@ static int cdrom_select_disc(struct cdrom_device_info *cdi, int slot) 
		slot = curslot;



	/* set media changed bits on both queues */

	cdi->mc_flags = 0x3;

	signal_media_change(cdi);

	if ((ret = cdrom_load_unload(cdi, slot)))

		return ret;
@@ -1521,7 +1527,7 @@ int media_changed(struct cdrom_device_info *cdi, int queue) 
	cdi->ioctl_events = 0;



	if (changed) {

		cdi->mc_flags = 0x3;    /* set bit on both queues */

		signal_media_change(cdi);

		ret |= 1;

		cdi->media_written = 0;

	}
@@ -2336,6 +2342,49 @@ static int cdrom_ioctl_media_changed(struct cdrom_device_info *cdi, 
	return ret;

}



/*

 * Media change detection with timing information.

 *

 * 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 (in ms) of the last known media change (by the caller).

 * Upon successful return, ioctl call will set arg->last_media_change

 * to the latest media change timestamp 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.

 */

static int cdrom_ioctl_timed_media_change(struct cdrom_device_info *cdi,

		unsigned long arg)

{

	int ret;

	struct cdrom_timed_media_change_info __user *info;

	struct cdrom_timed_media_change_info tmp_info;



	if (!CDROM_CAN(CDC_MEDIA_CHANGED))

		return -ENOSYS;



	info = (struct cdrom_timed_media_change_info __user *)arg;

	cd_dbg(CD_DO_IOCTL, "entering CDROM_TIMED_MEDIA_CHANGE\n");



	ret = cdrom_ioctl_media_changed(cdi, CDSL_CURRENT);

	if (ret < 0)

		return ret;



	if (copy_from_user(&tmp_info, info, sizeof(tmp_info)) != 0)

		return -EFAULT;



	tmp_info.media_flags = 0;

	if (tmp_info.last_media_change - cdi->last_media_change_ms < 0)

		tmp_info.media_flags |= MEDIA_CHANGED_FLAG;



	tmp_info.last_media_change = cdi->last_media_change_ms;



	if (copy_to_user(info, &tmp_info, sizeof(*info)) != 0)

		return -EFAULT;



	return 0;

}



static int cdrom_ioctl_set_options(struct cdrom_device_info *cdi,

		unsigned long arg)

{
@@ -3313,6 +3362,8 @@ int cdrom_ioctl(struct cdrom_device_info *cdi, struct block_device *bdev, 
		return cdrom_ioctl_eject_sw(cdi, arg);

	case CDROM_MEDIA_CHANGED:

		return cdrom_ioctl_media_changed(cdi, arg);

	case CDROM_TIMED_MEDIA_CHANGE:

		return cdrom_ioctl_timed_media_change(cdi, arg);

	case CDROM_SET_OPTIONS:

		return cdrom_ioctl_set_options(cdi, arg);

	case CDROM_CLEAR_OPTIONS:

include/linux/cdrom.h

+1 −0
Original line number Diff line number Diff line
@@ -64,6 +64,7 @@ struct cdrom_device_info { 
	int for_data;

	int (*exit)(struct cdrom_device_info *);

	int mrw_mode_page;

	__s64 last_media_change_ms;

};



struct cdrom_device_ops {

include/uapi/linux/cdrom.h

+19 −0
Original line number Diff line number Diff line
@@ -147,6 +147,8 @@ 
#define CDROM_NEXT_WRITABLE	0x5394	/* get next writable block */

#define CDROM_LAST_WRITTEN	0x5395	/* get last block written on disc */



#define CDROM_TIMED_MEDIA_CHANGE   0x5396  /* get the timestamp of the last media change */



/*******************************************************

 * CDROM IOCTL structures

 *******************************************************/
@@ -295,6 +297,23 @@ struct cdrom_generic_command 
	};

};



/* This struct is used by CDROM_TIMED_MEDIA_CHANGE */

struct cdrom_timed_media_change_info {

	__s64	last_media_change;	/* Timestamp of the last detected media

					 * change in ms. May be set by caller,

					 * updated upon successful return of

					 * ioctl.

					 */

	__u64	media_flags;		/* Flags returned by ioctl to indicate

					 * media status.

					 */

};

#define MEDIA_CHANGED_FLAG	0x1	/* Last detected media change was more

					 * recent than last_media_change set by

					 * caller.

					 */

/* other bits of media_flags available for future use */



/*

 * A CD-ROM physical sector size is 2048, 2052, 2056, 2324, 2332, 2336, 

 * 2340, or 2352 bytes long.