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

[Anisa Su <anisa.su887@gmail.com>]

On Thu, May 28, 2026 at 03:54:34PM -0700, Dave Jiang wrote:
> 
> 
> 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
> 
added
> > ---
> >  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
> 
updated
> > +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?
> 
oh yeah oops... replaced w/uuid_is_null()

> DJ
> 
Thanks,
Anisa
> > +		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)
>