block: factor out bd_may_claim()

Factor out bd_may_claim() from bd_claim(), add comments and apply a
couple of cosmetic edits.  This is to prepare for further updates to
claim path.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 47 insertions, 18 deletions

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 2a6d0193f139..e59440c7e1cf 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -661,41 +661,70 @@ void bd_forget(struct inode *inode)
                 iput(bdev->bd_inode);
 }
 
-int bd_claim(struct block_device *bdev, void *holder)
+/**
+ * bd_may_claim - test whether a block device can be claimed
+ * @bdev: block device of interest
+ * @whole: whole block device containing @bdev, may equal @bdev
+ * @holder: holder trying to claim @bdev
+ *
+ * Test whther @bdev can be claimed by @holder.
+ *
+ * CONTEXT:
+ * spin_lock(&bdev_lock).
+ *
+ * RETURNS:
+ * %true if @bdev can be claimed, %false otherwise.
+ */
+static bool bd_may_claim(struct block_device *bdev, struct block_device *whole,
+                         void *holder)
 {
-        int res;
-        spin_lock(&bdev_lock);
-
-        /* first decide result */
         if (bdev->bd_holder == holder)
-                res = 0;         /* already a holder */
+                return true;     /* already a holder */
         else if (bdev->bd_holder != NULL)
-                res = -EBUSY;    /* held by someone else */
+                return false;    /* held by someone else */
         else if (bdev->bd_contains == bdev)
-                res = 0;         /* is a whole device which isn't held */
+                return true;     /* is a whole device which isn't held */
 
-        else if (bdev->bd_contains->bd_holder == bd_claim)
-                res = 0;         /* is a partition of a device that is being partitioned */
-        else if (bdev->bd_contains->bd_holder != NULL)
-                res = -EBUSY;    /* is a partition of a held device */
+        else if (whole->bd_holder == bd_claim)
+                return true;     /* is a partition of a device that is being partitioned */
+        else if (whole->bd_holder != NULL)
+                return false;    /* is a partition of a held device */
         else
-                res = 0;         /* is a partition of an un-held device */
+                return true;     /* is a partition of an un-held device */
+}
 
-        /* now impose change */
-        if (res==0) {
+/**
+ * bd_claim - claim a block device
+ * @bdev: block device to claim
+ * @holder: holder trying to claim @bdev
+ *
+ * Try to claim @bdev.
+ *
+ * RETURNS:
+ * 0 if successful, -EBUSY if @bdev is already claimed.
+ */
+int bd_claim(struct block_device *bdev, void *holder)
+{
+        struct block_device *whole = bdev->bd_contains;
+        int res = -EBUSY;
+
+        spin_lock(&bdev_lock);
+
+        if (bd_may_claim(bdev, whole, holder)) {
                 /* note that for a whole device bd_holders
                  * will be incremented twice, and bd_holder will
                  * be set to bd_claim before being set to holder
                  */
-                bdev->bd_contains->bd_holders ++;
-                bdev->bd_contains->bd_holder = bd_claim;
+                whole->bd_holders++;
+                whole->bd_holder = bd_claim;
                 bdev->bd_holders++;
                 bdev->bd_holder = holder;
+                res = 0;
         }
+
         spin_unlock(&bdev_lock);
         return res;
 }
-
 EXPORT_SYMBOL(bd_claim);
 
 void bd_release(struct block_device *bdev)