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block: bd_start_claiming cleanup

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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@suse.de>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
This commit is contained in:
Nick Piggin 2010-05-26 01:51:19 +10:00 committed by Jens Axboe
parent cf3425707e
commit b0018361c3
1 changed files with 48 additions and 24 deletions
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72
fs/block_dev.c
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@ -706,8 +706,13 @@ 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.
@ -783,15 +788,47 @@ static void bd_abort_claiming(struct block_device *whole, void *holder)
__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.
@ -807,23 +844,10 @@ int bd_claim(struct block_device *bdev, void *holder)
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;
}
@ -1477,7 +1501,7 @@ static int blkdev_open(struct inode * inode, struct file * filp)
if (whole) {
if (res == 0)
BUG_ON(bd_claim(bdev, filp) != 0);
bd_finish_claiming(bdev, whole, filp);
else
bd_abort_claiming(whole, filp);
}
@ -1713,7 +1737,7 @@ struct block_device *open_bdev_exclusive(const char *path, fmode_t mode, void *h
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: