I don't like the subtle multi-context code in bd_claim (ie. detects where it
has been called based on bd_claiming). It seems clearer to just require a new
function to finish a 2-part claim.
Also improve commentary in bd_start_claiming as to how it should
be used.
Signed-off-by: Nick Piggin <npiggin@xxxxxxx>
Index: linux-2.6/fs/block_dev.c
===================================================================
--- linux-2.6.orig/fs/block_dev.c
+++ linux-2.6/fs/block_dev.c
@@ -710,8 +710,13 @@ retry:
* @bdev is about to be opened exclusively. Check @bdev can be opened
* exclusively and mark that an exclusive open is in progress. Each
* successful call to this function must be matched with a call to
- * either bd_claim() or bd_abort_claiming(). If this function
- * succeeds, the matching bd_claim() is guaranteed to succeed.
+ * either bd_finish_claiming() or bd_abort_claiming() (which do not
+ * fail).
+ *
+ * This function is used to gain exclusive access to the block device
+ * without actually causing other exclusive open attempts to fail. It
+ * should be used when the open sequence itself requires exclusive
+ * access but may subsequently fail.
*
* CONTEXT:
* Might sleep.
@@ -787,15 +792,47 @@ static void bd_abort_claiming(struct blo
__bd_abort_claiming(whole, holder); /* releases bdev_lock */
}
+/* increment holders when we have a legitimate claim. requires bdev_lock */
+static void __bd_claim(struct block_device *bdev, struct block_device *whole,
+ void *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
+ */
+ whole->bd_holders++;
+ whole->bd_holder = bd_claim;
+ bdev->bd_holders++;
+ bdev->bd_holder = holder;
+}
+
+/**
+ * bd_finish_claiming - finish claiming a block device
+ * @bdev: block device of interest (passed to bd_start_claiming())
+ * @whole: whole block device returned by bd_start_claiming()
+ * @holder: holder trying to claim @bdev
+ *
+ * Finish a claiming block started by bd_start_claiming().
+ *
+ * CONTEXT:
+ * Grabs and releases bdev_lock.
+ */
+static void bd_finish_claiming(struct block_device *bdev,
+ struct block_device *whole, void *holder)
+{
+ spin_lock(&bdev_lock);
+ BUG_ON(whole->bd_claiming != holder);
+ BUG_ON(!bd_may_claim(bdev, whole, holder));
+ __bd_claim(bdev, whole, holder);
+ __bd_abort_claiming(whole, holder); /* not actually an abort */
+}
+
/**
* bd_claim - claim a block device
* @bdev: block device to claim
* @holder: holder trying to claim @bdev
*
- * Try to claim @bdev which must have been opened successfully. This
- * function may be called with or without preceding
- * blk_start_claiming(). In the former case, this function is always
- * successful and terminates the claiming block.
+ * Try to claim @bdev which must have been opened successfully.
*
* CONTEXT:
* Might sleep.
@@ -811,23 +848,10 @@ int bd_claim(struct block_device *bdev,
might_sleep();
spin_lock(&bdev_lock);
-
res = bd_prepare_to_claim(bdev, whole, holder);
- if (res == 0) {
- /* 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
- */
- whole->bd_holders++;
- whole->bd_holder = bd_claim;
- bdev->bd_holders++;
- bdev->bd_holder = holder;
- }
-
- if (whole->bd_claiming)
- __bd_abort_claiming(whole, holder); /* releases bdev_lock */
- else
- spin_unlock(&bdev_lock);
+ if (res == 0)
+ __bd_claim(bdev, whole, holder);
+ spin_unlock(&bdev_lock);
return res;
}
@@ -1481,7 +1505,7 @@ static int blkdev_open(struct inode * in
if (whole) {
if (res == 0)
- BUG_ON(bd_claim(bdev, filp) != 0);
+ bd_finish_claiming(bdev, whole, filp);
else
bd_abort_claiming(whole, filp);
}
@@ -1717,7 +1741,7 @@ struct block_device *open_bdev_exclusive
if ((mode & FMODE_WRITE) && bdev_read_only(bdev))
goto out_blkdev_put;
- BUG_ON(bd_claim(bdev, holder) != 0);
+ bd_finish_claiming(bdev, whole, holder);
return bdev;
out_blkdev_put:
--
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