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

Christian Brauner
2023-03-30T06:33:11Z

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().