Re: [PATCH v13 4/9] fs, block: copy_file_range for def_blk_ops for direct block device

[Nitesh Shetty]

On 23/06/28 03:51PM, Damien Le Moal wrote:
> On 6/28/23 03:36, Nitesh Shetty wrote:
> > 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.
>
> ...if the device does not support copy offload or the device files are not open
> with O_DIRECT.
>
> No ?
Yes your right. We will fallback to generic_copy_file_range in either of
these cases.

> > Modify checks to allow bdevs to use copy_file_range.
> >
> > Suggested-by: Ming Lei <ming.lei@xxxxxxxxxx>
> > Signed-off-by: Anuj Gupta <anuj20.g@xxxxxxxxxxx>
> > Signed-off-by: Nitesh Shetty <nj.shetty@xxxxxxxxxxx>
> > ---
> >  block/blk-lib.c        | 26 ++++++++++++++++++++++++++
> >  block/fops.c           | 20 ++++++++++++++++++++
> >  fs/read_write.c        |  7 +++++--
> >  include/linux/blkdev.h |  4 ++++
> >  4 files changed, 55 insertions(+), 2 deletions(-)
> >
> > diff --git a/block/blk-lib.c b/block/blk-lib.c
> > index 09e0d5d51d03..7d8e09a99254 100644
> > --- a/block/blk-lib.c
> > +++ b/block/blk-lib.c
> > @@ -473,6 +473,32 @@ ssize_t blkdev_copy_offload(
> >  }
> >  EXPORT_SYMBOL_GPL(blkdev_copy_offload);
> >
> > +/* Copy source offset from source block device to destination block
> > + * device. Returns the length of bytes copied.
> > + */
>
> Multi-line comment style: start with a "/*" line please.
acked

> > +ssize_t blkdev_copy_offload_failfast(
>
> What is the "failfast" in the name for ?

We dont want failed copy offload IOs to fallback to block layer copy emulation.
We wanted a API to return error, if offload fails.

> > +		struct block_device *bdev_in, loff_t pos_in,
> > +		struct block_device *bdev_out, loff_t pos_out,
> > +		size_t len, gfp_t gfp_mask)
> > +{
> > +	struct request_queue *in_q = bdev_get_queue(bdev_in);
> > +	struct request_queue *out_q = bdev_get_queue(bdev_out);
> > +	ssize_t ret = 0;
>
> You do not need this initialization.

we need this initialization, because __blkdev_copy_offload return number of
bytes copied or error value.
So we can not return 0, incase of success/partial completion.
blkdev_copy_offload_failfast is expected to return number of bytes copied.

> > +
> > +	if (blkdev_copy_sanity_check(bdev_in, pos_in, bdev_out, pos_out, len))
> > +		return 0;
> > +
> > +	if (blk_queue_copy(in_q) && blk_queue_copy(out_q)) {
>
> Given that I think we do not allow copies between different devices, in_q and
> out_q should always be the same, no ?

acked, will update this.

> > +		ret = __blkdev_copy_offload(bdev_in, pos_in, bdev_out, pos_out,
> > +				len, NULL, NULL, gfp_mask);
>
> Same here. Why pass 2 bdevs if we only allow copies within the same device ?

acked, will update function arguments to take single bdev.

> > +		if (ret < 0)
> > +			return 0;
> > +	}
> > +
> > +	return ret;
>
> return 0;

Nack, explained above.

Thank you,
Nitesh Shetty