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>
diff --git a/drivers/cdrom/cdrom.c b/drivers/cdrom/cdrom.c
index bd2e5b1..89a6845 100644
--- a/drivers/cdrom/cdrom.c
+++ b/drivers/cdrom/cdrom.c
@@ -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: