block: flush MEDIA_CHANGE from drivers on close(2)

Currently, only open(2) is defined as the 'clearing' point.  It has
two roles - first, it's an acknowledgement from userland indicating
that the event has been received and kernel can clear pending states
and proceed to generate more events.  Secondly, it's passed on to
device drivers as a hint indicating that a synchronization point has
been reached and it might want to take a deeper look at the device.

The latter currently is only used by sr which uses two different
mechanisms - GET_EVENT_MEDIA_STATUS_NOTIFICATION and TEST_UNIT_READY
to discover events, where the former is lighter weight and safe to be
used repeatedly but may not provide full coverage.  Among other
things, GET_EVENT can't detect media removal while TUR can.

This patch makes close(2) - blkdev_put() - indicate clearing hint for
MEDIA_CHANGE to drivers.  disk_check_events() is renamed to
disk_flush_events() and updated to take @mask for events to flush
which is or'd to ev->clearing and will be passed to the driver on the
next ->check_events() invocation.

This change makes sr generate MEDIA_CHANGE when media is ejected from
userland - e.g. with eject(1).

Note: Given the current usage, it seems @clearing hint is needlessly
complex.  disk_clear_events() can simply clear all events and the hint
can be boolean @flush.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 14 insertions, 9 deletions

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 610e8e0b04b8..6ff7f070016f 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1447,6 +1447,8 @@ static int __blkdev_put(struct block_device *bdev, fmode_t mode, int for_part)
 
 int blkdev_put(struct block_device *bdev, fmode_t mode)
 {
+        mutex_lock(&bdev->bd_mutex);
+
         if (mode & FMODE_EXCL) {
                 bool bdev_free;
 
@@ -1455,7 +1457,6 @@ int blkdev_put(struct block_device *bdev, fmode_t mode)
                  * are protected with bdev_lock.  bd_mutex is to
                  * synchronize disk_holder unlinking.
                  */
-                mutex_lock(&bdev->bd_mutex);
                 spin_lock(&bdev_lock);
 
                 WARN_ON_ONCE(--bdev->bd_holders < 0);
@@ -1473,17 +1474,21 @@ int blkdev_put(struct block_device *bdev, fmode_t mode)
                  * If this was the last claim, remove holder link and
                  * unblock evpoll if it was a write holder.
                  */
-                if (bdev_free) {
-                        if (bdev->bd_write_holder) {
-                                disk_unblock_events(bdev->bd_disk);
-                                disk_check_events(bdev->bd_disk);
-                                bdev->bd_write_holder = false;
-                        }
+                if (bdev_free && bdev->bd_write_holder) {
+                        disk_unblock_events(bdev->bd_disk);
+                        bdev->bd_write_holder = false;
                 }
-
-                mutex_unlock(&bdev->bd_mutex);
         }
 
+        /*
+         * Trigger event checking and tell drivers to flush MEDIA_CHANGE
+         * event.  This is to ensure detection of media removal commanded
+         * from userland - e.g. eject(1).
+         */
+        disk_flush_events(bdev->bd_disk, DISK_EVENT_MEDIA_CHANGE);
+
+        mutex_unlock(&bdev->bd_mutex);
+
         return __blkdev_put(bdev, mode, 0);
 }
 EXPORT_SYMBOL(blkdev_put);