Re: [PATCH v10 20/31] cxl/region/extent: Expose dc_extent information in sysfs

[Dave Jiang <dave.jiang@intel.com>]

On 5/23/26 2:43 AM, Anisa Su wrote:
> From: Ira Weiny <ira.weiny@intel.com>
> 
> Extent information can be helpful to the user to coordinate memory
> usage with the external orchestrator and FM.
> 
> Expose the details of each dc_extent by creating the following sysfs
> entries.
> 
> 	/sys/bus/cxl/devices/dax_regionX/extentX.Y
> 	/sys/bus/cxl/devices/dax_regionX/extentX.Y/offset
> 	/sys/bus/cxl/devices/dax_regionX/extentX.Y/length
> 	/sys/bus/cxl/devices/dax_regionX/extentX.Y/uuid
> 
> Each dc_extent surfaces as its own extentX.Y device under the parent
> dax_region.  offset and length describe that dc_extent's HPA range,
> not an aggregate bounding box across the containing tagged
> allocation — so when a tagged allocation has multiple
> DPA-discontiguous extents, each is reported with its own offset and
> length.  uuid is the tag identifying the containing allocation; it
> is shared across dc_extents that belong to the same tagged
> allocation and is hidden for untagged extents.
> 
> Based on an original patch by Navneet Singh.
> 
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Reviewed-by: Fan Ni <fan.ni@samsung.com>
> Tested-by: Fan Ni <fan.ni@samsung.com>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>

Missing Anisa sign off

> ---
>  Documentation/ABI/testing/sysfs-bus-cxl | 36 +++++++++++++++
>  drivers/cxl/core/extent.c               | 58 +++++++++++++++++++++++++
>  2 files changed, 94 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> index 3080aef9ad67..38cf0a2894b9 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cxl
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -661,3 +661,39 @@ Description:
>  		The count is persistent across power loss and wraps back to 0
>  		upon overflow. If this file is not present, the device does not
>  		have the necessary support for dirty tracking.
> +
> +
> +What:		/sys/bus/cxl/devices/dax_regionX/extentX.Y/offset
> +Date:		May, 2025
> +KernelVersion:	v6.16

Update date and kernel version for all

> +Contact:	linux-cxl@vger.kernel.org
> +Description:
> +		(RO) [For Dynamic Capacity regions only] Users can use the
> +		extent information to create DAX devices on specific extents.
> +		This is done by creating and destroying DAX devices in specific
> +		sequences and looking at the mappings created.  Extent offset
> +		within the region.
> +
> +
> +What:		/sys/bus/cxl/devices/dax_regionX/extentX.Y/length
> +Date:		May, 2025
> +KernelVersion:	v6.16
> +Contact:	linux-cxl@vger.kernel.org
> +Description:
> +		(RO) [For Dynamic Capacity regions only] Users can use the
> +		extent information to create DAX devices on specific extents.
> +		This is done by creating and destroying DAX devices in specific
> +		sequences and looking at the mappings created.  Extent length
> +		within the region.
> +
> +
> +What:		/sys/bus/cxl/devices/dax_regionX/extentX.Y/uuid
> +Date:		May, 2025
> +KernelVersion:	v6.16
> +Contact:	linux-cxl@vger.kernel.org
> +Description:
> +		(RO) [For Dynamic Capacity regions only] Users can use the
> +		extent information to create DAX devices on specific extents.
> +		This is done by creating and destroying DAX devices in specific
> +		sequences and looking at the mappings created.  UUID of this
> +		extent.
> diff --git a/drivers/cxl/core/extent.c b/drivers/cxl/core/extent.c
> index f66fa8c600c5..34babfe032d1 100644
> --- a/drivers/cxl/core/extent.c
> +++ b/drivers/cxl/core/extent.c
> @@ -6,6 +6,63 @@
>  
>  #include "core.h"
>  
> +static ssize_t offset_show(struct device *dev, struct device_attribute *attr,
> +			   char *buf)
> +{
> +	struct dc_extent *dc_extent = to_dc_extent(dev);
> +
> +	return sysfs_emit(buf, "%#llx\n", dc_extent->hpa_range.start);
> +}
> +static DEVICE_ATTR_RO(offset);
> +
> +static ssize_t length_show(struct device *dev, struct device_attribute *attr,
> +			   char *buf)
> +{
> +	struct dc_extent *dc_extent = to_dc_extent(dev);
> +	u64 length = range_len(&dc_extent->hpa_range);
> +
> +	return sysfs_emit(buf, "%#llx\n", length);
> +}
> +static DEVICE_ATTR_RO(length);
> +
> +static ssize_t uuid_show(struct device *dev, struct device_attribute *attr,
> +			 char *buf)
> +{
> +	struct dc_extent *dc_extent = to_dc_extent(dev);
> +
> +	return sysfs_emit(buf, "%pUb\n", &dc_extent->group->uuid);
> +}
> +static DEVICE_ATTR_RO(uuid);
> +
> +static struct attribute *dc_extent_attrs[] = {
> +	&dev_attr_offset.attr,
> +	&dev_attr_length.attr,
> +	&dev_attr_uuid.attr,
> +	NULL
> +};
> +
> +static uuid_t empty_uuid = { 0 };
> +
> +static umode_t dc_extent_visible(struct kobject *kobj,
> +				 struct attribute *a, int n)
> +{
> +	struct device *dev = kobj_to_dev(kobj);
> +	struct dc_extent *dc_extent = to_dc_extent(dev);
> +
> +	if (a == &dev_attr_uuid.attr &&
> +	    uuid_equal(&dc_extent->group->uuid, &empty_uuid))'

uuid_is_null() can be used?

DJ

> +		return 0;
> +
> +	return a->mode;
> +}
> +
> +static const struct attribute_group dc_extent_attribute_group = {
> +	.attrs = dc_extent_attrs,
> +	.is_visible = dc_extent_visible,
> +};
> +
> +__ATTRIBUTE_GROUPS(dc_extent_attribute);
> +
>  
>  static void cxled_release_extent(struct cxl_endpoint_decoder *cxled,
>  				 struct dc_extent *dc_extent)
> @@ -93,6 +150,7 @@ static void dc_extent_release(struct device *dev)
>  static const struct device_type dc_extent_type = {
>  	.name = "extent",
>  	.release = dc_extent_release,
> +	.groups = dc_extent_attribute_groups,
>  };
>  
>  bool is_dc_extent(struct device *dev)