rbd: fix and simplify rbd_ioctl_set_ro()

->open_count/-EBUSY check is bogus and wrong: when an open device is
set read-only, blkdev_write_iter() refuses further writes with -EPERM.
This is standard behaviour and all other block devices allow this.

set_disk_ro() call is also problematic: we affect the entire device
when called on a single partition.

All rbd_ioctl_set_ro() needs to do is refuse ro -> rw transition for
mapped snapshots.  Everything else can be handled by generic code.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

1 files changed, 6 insertions, 28 deletions

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index adc877dfef5c..fb7cb38a6d83 100644
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -640,46 +640,24 @@ static void rbd_release(struct gendisk *disk, fmode_t mode)
 
 static int rbd_ioctl_set_ro(struct rbd_device *rbd_dev, unsigned long arg)
 {
-        int ret = 0;
-        int val;
-        bool ro;
-        bool ro_changed = false;
+        int ro;
 
-        /* get_user() may sleep, so call it before taking rbd_dev->lock */
-        if (get_user(val, (int __user *)(arg)))
+        if (get_user(ro, (int __user *)arg))
                 return -EFAULT;
 
-        ro = val ? true : false;
-        /* Snapshot doesn't allow to write*/
+        /* Snapshots can't be marked read-write */
         if (rbd_dev->spec->snap_id != CEPH_NOSNAP && !ro)
                 return -EROFS;
 
-        spin_lock_irq(&rbd_dev->lock);
-        /* prevent others open this device */
-        if (rbd_dev->open_count > 1) {
-                ret = -EBUSY;
-                goto out;
-        }
-
-        if (rbd_dev->mapping.read_only != ro) {
-                rbd_dev->mapping.read_only = ro;
-                ro_changed = true;
-        }
-
-out:
-        spin_unlock_irq(&rbd_dev->lock);
-        /* set_disk_ro() may sleep, so call it after releasing rbd_dev->lock */
-        if (ret == 0 && ro_changed)
-                set_disk_ro(rbd_dev->disk, ro ? 1 : 0);
-
-        return ret;
+        /* Let blkdev_roset() handle it */
+        return -ENOTTY;
 }
 
 static int rbd_ioctl(struct block_device *bdev, fmode_t mode,
                         unsigned int cmd, unsigned long arg)
 {
         struct rbd_device *rbd_dev = bdev->bd_disk->private_data;
-        int ret = 0;
+        int ret;
 
         switch (cmd) {
         case BLKROSET: