Re: [PATCH RFC] loop: make partition scanning reliable

[Tejun Heo <tj@kernel.org>]

Hello, David.

On Mon, Jan 26, 2015 at 11:15:19AM +0100, David Herrmann wrote:
> -static int blkdev_reread_part(struct block_device *bdev)
> +int blkdev_reread_part(struct block_device *bdev, int skipbusy)
>  {
>  	struct gendisk *disk = bdev->bd_disk;
>  	int res;
> @@ -159,12 +159,15 @@ static int blkdev_reread_part(struct block_device *bdev)
>  		return -EINVAL;
>  	if (!capable(CAP_SYS_ADMIN))
>  		return -EACCES;
> -	if (!mutex_trylock(&bdev->bd_mutex))
> +	if (!skipbusy)
> +		mutex_lock(&bdev->bd_mutex);
> +	else if (!mutex_trylock(&bdev->bd_mutex))
>  		return -EBUSY;

Do we actually need the mutex_trylock() path?  Why can't we just
always grab the mutex?

...
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index 6cb1beb..4047985 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -637,7 +637,7 @@ out:
>   * new backing store is the same size and type as the old backing store.
>   */
>  static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,
> -			  unsigned int arg)
> +			  unsigned int arg, int *rrpart)

bool *rrpart would be better but can't we communicate this through the
return value?  Wouldn't that be prettier?

Thanks.

-- 
tejun