cdrom: add ->check_events() support

In principle, cdrom just needs to pass through ->check_events() but
CDROM_MEDIA_CHANGED ioctl makes things a bit more complex.  Just as
with ->media_changed() support, cdrom code needs to buffer the events
and serve them to ioctl and vfs as requested.

As the code has to deal with both ->check_events() and
->media_changed(), and vfs and ioctl event buffering, this patch adds
check_events caching on top of the existing cdi->mc_flags buffering.

It may be a good idea to deprecate CDROM_MEDIA_CHANGED ioctl and
remove all this mess.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

2 files changed, 58 insertions, 3 deletions

diff --git a/drivers/cdrom/cdrom.c b/drivers/cdrom/cdrom.c
index af13c62dc473..1ea8f8d363c6 100644
--- a/drivers/cdrom/cdrom.c
+++ b/drivers/cdrom/cdrom.c
@@ -1348,7 +1348,10 @@ static int cdrom_select_disc(struct cdrom_device_info *cdi, int slot)
         if (!CDROM_CAN(CDC_SELECT_DISC))
                 return -EDRIVE_CANT_DO_THIS;
 
-        (void) cdi->ops->media_changed(cdi, slot);
+        if (cdi->ops->check_events)
+                cdi->ops->check_events(cdi, 0, slot);
+        else
+                cdi->ops->media_changed(cdi, slot);
 
         if (slot == CDSL_NONE) {
                 /* set media changed bits, on both queues */
@@ -1392,6 +1395,41 @@ static int cdrom_select_disc(struct cdrom_device_info *cdi, int slot)
         return slot;
 }
 
+/*
+ * As cdrom implements an extra ioctl consumer for media changed
+ * event, it needs to buffer ->check_events() output, such that event
+ * is not lost for both the usual VFS and ioctl paths.
+ * cdi->{vfs|ioctl}_events are used to buffer pending events for each
+ * path.
+ *
+ * XXX: Locking is non-existent.  cdi->ops->check_events() can be
+ * called in parallel and buffering fields are accessed without any
+ * exclusion.  The original media_changed code had the same problem.
+ * It might be better to simply deprecate CDROM_MEDIA_CHANGED ioctl
+ * and remove this cruft altogether.  It doesn't have much usefulness
+ * at this point.
+ */
+static void cdrom_update_events(struct cdrom_device_info *cdi,
+                                unsigned int clearing)
+{
+        unsigned int events;
+
+        events = cdi->ops->check_events(cdi, clearing, CDSL_CURRENT);
+        cdi->vfs_events |= events;
+        cdi->ioctl_events |= events;
+}
+
+unsigned int cdrom_check_events(struct cdrom_device_info *cdi,
+                                unsigned int clearing)
+{
+        unsigned int events;
+
+        cdrom_update_events(cdi, clearing);
+        events = cdi->vfs_events;
+        cdi->vfs_events = 0;
+        return events;
+}
+
 /* We want to make media_changed accessible to the user through an
  * ioctl. The main problem now is that we must double-buffer the
  * low-level implementation, to assure that the VFS and the user both
@@ -1403,15 +1441,26 @@ int media_changed(struct cdrom_device_info *cdi, int queue)
 {
         unsigned int mask = (1 << (queue & 1));
         int ret = !!(cdi->mc_flags & mask);
+        bool changed;
 
         if (!CDROM_CAN(CDC_MEDIA_CHANGED))
-            return ret;
+                return ret;
+
         /* changed since last call? */
-        if (cdi->ops->media_changed(cdi, CDSL_CURRENT)) {
+        if (cdi->ops->check_events) {
+                BUG_ON(!queue); /* shouldn't be called from VFS path */
+                cdrom_update_events(cdi, DISK_EVENT_MEDIA_CHANGE);
+                changed = cdi->ioctl_events & DISK_EVENT_MEDIA_CHANGE;
+                cdi->ioctl_events = 0;
+        } else
+                changed = cdi->ops->media_changed(cdi, CDSL_CURRENT);
+
+        if (changed) {
                 cdi->mc_flags = 0x3;    /* set bit on both queues */
                 ret |= 1;
                 cdi->media_written = 0;
         }
+
         cdi->mc_flags &= ~mask;         /* clear bit */
         return ret;
 }
diff --git a/include/linux/cdrom.h b/include/linux/cdrom.h
index 78e904796622..35eae4b67503 100644
--- a/include/linux/cdrom.h
+++ b/include/linux/cdrom.h
@@ -946,6 +946,8 @@ struct cdrom_device_info {
 /* device-related storage */
         unsigned int options    : 30;   /* options flags */
         unsigned mc_flags       : 2;    /* media change buffer flags */
+        unsigned int vfs_events;        /* cached events for vfs path */
+        unsigned int ioctl_events;      /* cached events for ioctl path */
         int use_count;                  /* number of times device opened */
         char name[20];                  /* name of the device type */
 /* per-device flags */
@@ -965,6 +967,8 @@ struct cdrom_device_ops {
         int (*open) (struct cdrom_device_info *, int);
         void (*release) (struct cdrom_device_info *);
         int (*drive_status) (struct cdrom_device_info *, int);
+        unsigned int (*check_events) (struct cdrom_device_info *cdi,
+                                      unsigned int clearing, int slot);
         int (*media_changed) (struct cdrom_device_info *, int);
         int (*tray_move) (struct cdrom_device_info *, int);
         int (*lock_door) (struct cdrom_device_info *, int);
@@ -993,6 +997,8 @@ extern int cdrom_open(struct cdrom_device_info *cdi, struct block_device *bdev,
 extern void cdrom_release(struct cdrom_device_info *cdi, fmode_t mode);
 extern int cdrom_ioctl(struct cdrom_device_info *cdi, struct block_device *bdev,
                        fmode_t mode, unsigned int cmd, unsigned long arg);
+extern unsigned int cdrom_check_events(struct cdrom_device_info *cdi,
+                                       unsigned int clearing);
 extern int cdrom_media_changed(struct cdrom_device_info *);
 
 extern int register_cdrom(struct cdrom_device_info *cdi);