[PATCH] rbd: do not allow remove of mounted-on image

[Alex Elder <elder@inktank.com>]

There is no check in rbd_remove() to see if anybody holds ope the
image being removed.  That's not cool.

Add a simple open count that goes up and down with opens and closes
(releases) of the device, and don't allow an rbd image to be removed
if the count is non-zero.  Both functions are protected by the
bd_mutex so there's no need for any other concurrency protection.

Signed-off-by: Alex Elder <elder@inktank.com>
---
 drivers/block/rbd.c |    9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index fba0822..9d9a2f3 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -255,6 +255,7 @@ struct rbd_device {

 	/* sysfs related */
 	struct device		dev;
+	unsigned long		open_count;
 };

 static DEFINE_MUTEX(ctl_mutex);	  /* Serialize open/close/setup/teardown */
@@ -358,6 +359,7 @@ static int rbd_open(struct block_device *bdev,
fmode_t mode)

 	rbd_get_dev(rbd_dev);
 	set_device_ro(bdev, rbd_dev->mapping.read_only);
+	rbd_dev->open_count++;

 	return 0;
 }
@@ -366,6 +368,8 @@ static int rbd_release(struct gendisk *disk, fmode_t
mode)
 {
 	struct rbd_device *rbd_dev = disk->private_data;

+	rbd_assert(rbd_dev->open_count > 0);
+	rbd_dev->open_count--;
 	rbd_put_dev(rbd_dev);

 	return 0;
@@ -3764,6 +3768,11 @@ static ssize_t rbd_remove(struct bus_type *bus,
 		goto done;
 	}

+	if (rbd_dev->open_count) {
+		ret = -EBUSY;
+		goto done;
+	}
+
 	rbd_remove_all_snaps(rbd_dev);
 	rbd_bus_del_dev(rbd_dev);

-- 
1.7.9.5