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: -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html