Re: [dm-devel] [PATCH v6 5/5] loop: Add support for provision requests

[Brian Foster <bfoster@redhat.com>]

On Fri, May 05, 2023 at 11:29:09PM -0700, Sarthak Kukreti wrote:
> Add support for provision requests to loopback devices.
> Loop devices will configure provision support based on
> whether the underlying block device/file can support
> the provision request and upon receiving a provision bio,
> will map it to the backing device/storage. For loop devices
> over files, a REQ_OP_PROVISION request will translate to
> an fallocate mode 0 call on the backing file.
> 
> Signed-off-by: Sarthak Kukreti <sarthakkukreti@chromium.org>
> ---
>  drivers/block/loop.c | 42 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 42 insertions(+)
> 
> diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> index bc31bb7072a2..13c4b4f8b9c1 100644
> --- a/drivers/block/loop.c
> +++ b/drivers/block/loop.c
> @@ -327,6 +327,24 @@ static int lo_fallocate(struct loop_device *lo, struct request *rq, loff_t pos,
>  	return ret;
>  }
>  
> +static int lo_req_provision(struct loop_device *lo, struct request *rq, loff_t pos)
> +{
> +	struct file *file = lo->lo_backing_file;
> +	struct request_queue *q = lo->lo_queue;
> +	int ret;
> +
> +	if (!q->limits.max_provision_sectors) {
> +		ret = -EOPNOTSUPP;
> +		goto out;
> +	}
> +
> +	ret = file->f_op->fallocate(file, 0, pos, blk_rq_bytes(rq));
> +	if (unlikely(ret && ret != -EINVAL && ret != -EOPNOTSUPP))
> +		ret = -EIO;
> + out:
> +	return ret;
> +}
> +
>  static int lo_req_flush(struct loop_device *lo, struct request *rq)
>  {
>  	int ret = vfs_fsync(lo->lo_backing_file, 0);
> @@ -488,6 +506,8 @@ static int do_req_filebacked(struct loop_device *lo, struct request *rq)
>  				FALLOC_FL_PUNCH_HOLE);
>  	case REQ_OP_DISCARD:
>  		return lo_fallocate(lo, rq, pos, FALLOC_FL_PUNCH_HOLE);
> +	case REQ_OP_PROVISION:
> +		return lo_req_provision(lo, rq, pos);

Hi Sarthak,

The only thing that stands out to me is the separate lo_req_provision()
helper here. It seems it might be a little cleaner to extend and reuse
lo_req_fallocate()..? But that's not something I feel strongly about, so
this all looks pretty good to me either way, FWIW.

Brian

>  	case REQ_OP_WRITE:
>  		if (cmd->use_aio)
>  			return lo_rw_aio(lo, cmd, pos, ITER_SOURCE);
> @@ -754,6 +774,25 @@ static void loop_sysfs_exit(struct loop_device *lo)
>  				   &loop_attribute_group);
>  }
>  
> +static void loop_config_provision(struct loop_device *lo)
> +{
> +	struct file *file = lo->lo_backing_file;
> +	struct inode *inode = file->f_mapping->host;
> +
> +	/*
> +	 * If the backing device is a block device, mirror its provisioning
> +	 * capability.
> +	 */
> +	if (S_ISBLK(inode->i_mode)) {
> +		blk_queue_max_provision_sectors(lo->lo_queue,
> +			bdev_max_provision_sectors(I_BDEV(inode)));
> +	} else if (file->f_op->fallocate) {
> +		blk_queue_max_provision_sectors(lo->lo_queue, UINT_MAX >> 9);
> +	} else {
> +		blk_queue_max_provision_sectors(lo->lo_queue, 0);
> +	}
> +}
> +
>  static void loop_config_discard(struct loop_device *lo)
>  {
>  	struct file *file = lo->lo_backing_file;
> @@ -1092,6 +1131,7 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
>  	blk_queue_io_min(lo->lo_queue, bsize);
>  
>  	loop_config_discard(lo);
> +	loop_config_provision(lo);
>  	loop_update_rotational(lo);
>  	loop_update_dio(lo);
>  	loop_sysfs_init(lo);
> @@ -1304,6 +1344,7 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
>  	}
>  
>  	loop_config_discard(lo);
> +	loop_config_provision(lo);
>  
>  	/* update dio if lo_offset or transfer is changed */
>  	__loop_update_dio(lo, lo->use_dio);
> @@ -1830,6 +1871,7 @@ static blk_status_t loop_queue_rq(struct blk_mq_hw_ctx *hctx,
>  	case REQ_OP_FLUSH:
>  	case REQ_OP_DISCARD:
>  	case REQ_OP_WRITE_ZEROES:
> +	case REQ_OP_PROVISION:
>  		cmd->use_aio = false;
>  		break;
>  	default:
> -- 
> 2.40.1.521.gf1e218fcd8-goog
> 

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