[Devel] [PATCH RH9 v2 2/8] dm: add llseek_hole infrastructure

[Alexander Atanasov]

On 16.08.23 12:32, Andrey Zhadchenko wrote:
> Add new function to target_type, so any dm devices may realize it
> Implement intermediate llseek_hole() on device-mapper layer, do some simple
> checks.
> 
> Feature: dm: implement SEEK_HOLE for dm-qcow2 and dm-ploop
> https://jira.vzint.dev/browse/PSBM-145746
> Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>
> 
> ---
> v2: fix return and goto inconsistency
> 
>   drivers/md/dm.c               | 41 +++++++++++++++++++++++++++++++++++
>   include/linux/device-mapper.h |  4 ++++
>   2 files changed, 45 insertions(+)
> 
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 7e5c61a75eeb..d592c023b090 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -484,6 +484,45 @@ static int dm_blk_ioctl(struct block_device *bdev, fmode_t mode,
>   	return r;
>   }
>   
> +static loff_t dm_llseek_hole(struct block_device *bdev, loff_t offset, int whence)
> +{
> +	struct mapped_device *md = bdev->bd_disk->private_data;
> +	struct dm_table *table;
> +	struct dm_target *ti;
> +	int srcu_idx;
> +	loff_t ret;
> +
> +	table = dm_get_live_table(md, &srcu_idx);
> +	if (!table || !dm_table_get_size(table))
> +		return -ENOTTY;
> +
> +	/*
> +	 * For now we only support devices that have a single target.
> +	 * But probably it is not hard to break it to a few requests to a different
> +	 * targets
> +	 */
> +	if (table->num_targets != 1)
> +		return -EOPNOTSUPP;


multipath, tracking and push_backup are all possible targets (that get 
used) so any combination can increase the count - shouldn't this be TODO?

> +	ti = dm_table_get_target(table, 0);
> +
> +	if (dm_suspended_md(md)) {
> +		ret = -EAGAIN;
> +		goto out;
> +	}
> +
> +	if (!ti->type->llseek_hole) {
> +		ret = -EINVAL;

EOPNOTSUPP - may be swap with num_targets != 1 error - which will be 
EINVAL due to the argument - while here it is not supported - not an 
issue with the arguments ?

> +		goto out;
> +	}
> +
> +	ret = ti->type->llseek_hole(ti, offset, whence);
> +
> +out:
> +	dm_put_live_table(md, srcu_idx);
> +	return ret;
> +}
> +
>   u64 dm_start_time_ns_from_clone(struct bio *bio)
>   {
>   	return jiffies_to_nsecs(clone_to_tio(bio)->io->start_time);
> @@ -3255,6 +3294,7 @@ static const struct block_device_operations dm_blk_dops = {
>   	.getgeo = dm_blk_getgeo,
>   	.report_zones = dm_blk_report_zones,
>   	.pr_ops = &dm_pr_ops,
> +	.llseek_hole = &dm_llseek_hole,

Why &dm_llseek_hole and not just dm_llseek_hole - like the other 
function assignments?

>   	.owner = THIS_MODULE
>   };
>   
> @@ -3264,6 +3304,7 @@ static const struct block_device_operations dm_rq_blk_dops = {
>   	.ioctl = dm_blk_ioctl,
>   	.getgeo = dm_blk_getgeo,
>   	.pr_ops = &dm_pr_ops,
> +	.llseek_hole = &dm_llseek_hole,

ditto


-- 
Regards,
Alexander Atanasov