Re: [PATCH 5/9] block: introduce holder ops

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On Fri, May 05, 2023 at 01:51:28PM -0400, Christoph Hellwig wrote:
> Add a new blk_holder_ops structure, which is passed to blkdev_get_by_* and
> installed in the block_device for exclusive claims.  It will be used to
> allow the block layer to call back into the user of the block device for
> thing like notification of a removed device or a device resize.
> 
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---

...

> @@ -542,7 +543,8 @@ static void bd_clear_claiming(struct block_device *whole, void *holder)
>   * Finish exclusive open of a block device. Mark the device as exlusively
>   * open by the holder and wake up all waiters for exclusive open to finish.
>   */
> -static void bd_finish_claiming(struct block_device *bdev, void *holder)
> +static void bd_finish_claiming(struct block_device *bdev, void *holder,
> +		const struct blk_holder_ops *hops)
>  {
>  	struct block_device *whole = bdev_whole(bdev);
>  
> @@ -555,7 +557,10 @@ static void bd_finish_claiming(struct block_device *bdev, void *holder)
>  	whole->bd_holders++;
>  	whole->bd_holder = bd_may_claim;
>  	bdev->bd_holders++;
> +	mutex_lock(&bdev->bd_holder_lock);
>  	bdev->bd_holder = holder;
> +	bdev->bd_holder_ops = hops;
> +	mutex_unlock(&bdev->bd_holder_lock);
>  	bd_clear_claiming(whole, holder);
>  	mutex_unlock(&bdev_lock);
>  }

I guess the holder ops may be override in case of multiple claim, can
this be one problem from the holder ops user viewpoint? Or
warn_on_once(bdev->bd_holder_ops && bdev->bd_holder_ops != hops) is needed here?


Thanks,
Ming




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