Re: [dm-devel] [PATCH v8 4/9] fs, block: copy_file_range for def_blk_ops for direct block device.

[Christian Brauner <brauner@kernel.org>]

On Mon, Mar 27, 2023 at 02:10:52PM +0530, Anuj Gupta wrote:
> From: Nitesh Shetty <nj.shetty@samsung.com>
> 
> For direct block device opened with O_DIRECT, use copy_file_range to
> issue device copy offload, and fallback to generic_copy_file_range incase
> device copy offload capability is absent.
> Modify checks to allow bdevs to use copy_file_range.
> 
> Suggested-by: Ming Lei <ming.lei@redhat.com>
> Signed-off-by: Anuj Gupta <anuj20.g@samsung.com>
> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
> ---
>  block/blk-lib.c        | 22 ++++++++++++++++++++++
>  block/fops.c           | 20 ++++++++++++++++++++
>  fs/read_write.c        | 11 +++++++++--
>  include/linux/blkdev.h |  3 +++
>  4 files changed, 54 insertions(+), 2 deletions(-)
> 
> diff --git a/block/blk-lib.c b/block/blk-lib.c
> index a21819e59b29..c288573c7e77 100644
> --- a/block/blk-lib.c
> +++ b/block/blk-lib.c
> @@ -475,6 +475,28 @@ static inline bool blk_check_copy_offload(struct request_queue *q_in,
>  	return blk_queue_copy(q_in) && blk_queue_copy(q_out);
>  }
>  
> +int blkdev_copy_offload(struct block_device *bdev_in, loff_t pos_in,
> +		      struct block_device *bdev_out, loff_t pos_out, size_t len,
> +		      cio_iodone_t end_io, void *private, gfp_t gfp_mask)
> +{
> +	struct request_queue *in_q = bdev_get_queue(bdev_in);
> +	struct request_queue *out_q = bdev_get_queue(bdev_out);
> +	int ret = -EINVAL;

Why initialize to -EINVAL if blk_copy_sanity_check() initializes it
right away anyway?

> +	bool offload = false;

Same thing with initializing offload.

> +
> +	ret = blk_copy_sanity_check(bdev_in, pos_in, bdev_out, pos_out, len);
> +	if (ret)
> +		return ret;
> +
> +	offload = blk_check_copy_offload(in_q, out_q);
> +	if (offload)
> +		ret = __blk_copy_offload(bdev_in, pos_in, bdev_out, pos_out,
> +				len, end_io, private, gfp_mask);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(blkdev_copy_offload);
> +
>  /*
>   * @bdev_in:	source block device
>   * @pos_in:	source offset
> diff --git a/block/fops.c b/block/fops.c
> index d2e6be4e3d1c..3b7c05831d5c 100644
> --- a/block/fops.c
> +++ b/block/fops.c
> @@ -611,6 +611,25 @@ static ssize_t blkdev_read_iter(struct kiocb *iocb, struct iov_iter *to)
>  	return ret;
>  }
>  
> +static ssize_t blkdev_copy_file_range(struct file *file_in, loff_t pos_in,
> +				struct file *file_out, loff_t pos_out,
> +				size_t len, unsigned int flags)
> +{
> +	struct block_device *in_bdev = I_BDEV(bdev_file_inode(file_in));
> +	struct block_device *out_bdev = I_BDEV(bdev_file_inode(file_out));
> +	int comp_len = 0;
> +
> +	if ((file_in->f_iocb_flags & IOCB_DIRECT) &&
> +		(file_out->f_iocb_flags & IOCB_DIRECT))
> +		comp_len = blkdev_copy_offload(in_bdev, pos_in, out_bdev,
> +				 pos_out, len, NULL, NULL, GFP_KERNEL);
> +	if (comp_len != len)
> +		comp_len = generic_copy_file_range(file_in, pos_in + comp_len,
> +			file_out, pos_out + comp_len, len - comp_len, flags);

I'm not deeply familiar with this code but this looks odd. It at least
seems possible that comp_len could be -EINVAL and len 20 at which point
you'd be doing len - comp_len aka 20 - 22 = -2 in generic_copy_file_range().

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