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

[Nitesh Shetty <nj.shetty@samsung.com>]

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On Wed, Mar 29, 2023 at 02:14:40PM +0200, Christian Brauner wrote:
> 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?
> 

acked.

> > +	bool offload = false;
> 
> Same thing with initializing offload.
> 
acked

> > +
> > +	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().

comp_len should be 0 incase of error. We do agree, some function
description needs to be updated. We will recheck this completion path to
make sure not to return negative value, incase of failure.

Thank You,
Nitesh Shetty

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