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Message-Id: <20210829143735.512146-1-lumip@lumip.de>
Date: Sun, 29 Aug 2021 17:37:37 +0300
From: Lukas Prediger <lumip@...ip.de>
To: axboe@...nel.dk
Cc: linux-kernel@...r.kernel.org, Lukas Prediger <lumip@...ip.de>
Subject: [PATCH v2] 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@...ip.de>
---
Second version based on your feedback for the first
attempt. Please let me know if further changes are required.
---
Documentation/cdrom/cdrom-standard.rst | 11 ++++
Documentation/userspace-api/ioctl/cdrom.rst | 3 ++
drivers/cdrom/cdrom.c | 56 +++++++++++++++++++--
include/linux/cdrom.h | 1 +
include/uapi/linux/cdrom.h | 15 ++++++
5 files changed, 82 insertions(+), 4 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_.
diff --git a/Documentation/userspace-api/ioctl/cdrom.rst b/Documentation/userspace-api/ioctl/cdrom.rst
index 3b4c0506de46..bac5bbf93ca0 100644
--- a/Documentation/userspace-api/ioctl/cdrom.rst
+++ b/Documentation/userspace-api/ioctl/cdrom.rst
@@ -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
diff --git a/drivers/cdrom/cdrom.c b/drivers/cdrom/cdrom.c
index feb827eefd1a..a040a867f6a2 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;
}
@@ -2391,6 +2397,46 @@ 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.has_changed = ((tmp_info.last_media_change - cdi->last_media_change_ms) < 0);
+ 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)
{
@@ -3375,6 +3421,8 @@ 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:
diff --git a/include/linux/cdrom.h b/include/linux/cdrom.h
index f48d0a31deae..7c10b564db29 100644
--- a/include/linux/cdrom.h
+++ b/include/linux/cdrom.h
@@ -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 {
diff --git a/include/uapi/linux/cdrom.h b/include/uapi/linux/cdrom.h
index 6c34f6e2f1f7..9b17868667ed 100644
--- a/include/uapi/linux/cdrom.h
+++ b/include/uapi/linux/cdrom.h
@@ -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 +297,19 @@ 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 has_changed; /* Set to 1 by ioctl if last detected media
+ * change was more recent than
+ * last_media_change set by caller.
+ */
+};
+
/*
* A CD-ROM physical sector size is 2048, 2052, 2056, 2324, 2332, 2336,
* 2340, or 2352 bytes long.
--
2.25.1
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