On Thu, 5 Jun 2025, John Garry wrote:
> Currently we use min io size as the chunk size when deciding on the limit
> of atomic write size.
>
> Using min io size is not reliable, as this may be mutated when stacking
> the bottom device limits.
>
> The block stacking limits will rely on chunk_sectors in future, so set
> this value (to the chunk size).
>
> Introduce a flag - DM_TARGET_STRIPED - and check this in
> dm_set_device_limits() when setting this limit.
>
> Signed-off-by: John Garry <john.g.garry@xxxxxxxxxx>
> ---
> drivers/md/dm-stripe.c | 3 ++-
> drivers/md/dm-table.c | 4 ++++
> include/linux/device-mapper.h | 3 +++
> 3 files changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/md/dm-stripe.c b/drivers/md/dm-stripe.c
> index a7dc04bd55e5..c30df6715149 100644
> --- a/drivers/md/dm-stripe.c
> +++ b/drivers/md/dm-stripe.c
> @@ -466,7 +466,8 @@ static struct target_type stripe_target = {
> .name = "striped",
> .version = {1, 7, 0},
> .features = DM_TARGET_PASSES_INTEGRITY | DM_TARGET_NOWAIT |
> - DM_TARGET_ATOMIC_WRITES | DM_TARGET_PASSES_CRYPTO,
> + DM_TARGET_ATOMIC_WRITES | DM_TARGET_PASSES_CRYPTO |
> + DM_TARGET_STRIPED,
> .module = THIS_MODULE,
> .ctr = stripe_ctr,
> .dtr = stripe_dtr,
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index 24a857ff6d0b..4f1f7173740c 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -430,6 +430,10 @@ static int dm_set_device_limits(struct dm_target *ti, struct dm_dev *dev,
> return 0;
> }
>
> + /* For striped types, limit the chunk_sectors to the chunk size */
> + if (dm_target_supports_striped(ti->type))
> + limits->chunk_sectors = len >> SECTOR_SHIFT;
> +
len is already in sectors, so why do we shift it right?
Could this logic be moved to the function stripe_io_hints, so that we
don't have to add a new flag for that and that we don't have to modify the
generic dm code?
Mikulas
> mutex_lock(&q->limits_lock);
> /*
> * BLK_FEAT_ATOMIC_WRITES is not inherited from the bottom device in
> diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
> index cb95951547ab..a863523b69ee 100644
> --- a/include/linux/device-mapper.h
> +++ b/include/linux/device-mapper.h
> @@ -309,6 +309,9 @@ struct target_type {
> #define DM_TARGET_ATOMIC_WRITES 0x00000400
> #define dm_target_supports_atomic_writes(type) ((type)->features & DM_TARGET_ATOMIC_WRITES)
>
> +#define DM_TARGET_STRIPED 0x00000800
> +#define dm_target_supports_striped(type) ((type)->features & DM_TARGET_STRIPED)
> +
> struct dm_target {
> struct dm_table *table;
> struct target_type *type;
> --
> 2.31.1
>
