Re: [PATCH v3 19/25] cxl/region/extent: Expose region extent information in sysfs

[Dave Jiang <dave.jiang@xxxxxxxxx>]

On 8/16/24 7:44 AM, ira.weiny@xxxxxxxxx wrote:
> From: Navneet Singh <navneet.singh@xxxxxxxxx>
> 
> Extent information can be helpful to the user to coordinate memory usage
> with the external orchestrator and FM.
> 
> Expose the details of region extents 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/tag
> 
> Signed-off-by: Navneet Singh <navneet.singh@xxxxxxxxx>
> Co-developed-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> 
> ---
> Changes:
> [iweiny: split this out]
> [Jonathan: add documentation for extent sysfs]
> [Jonathan/djbw: s/label/tag]
> [Jonathan/djbw: treat tag as uuid]
> [djbw: use __ATTRIBUTE_GROUPS]
> [djbw: make tag invisible if it is empty]
> [djbw/iweiny: use conventional id names for extents; extentX.Y]
> ---
>  Documentation/ABI/testing/sysfs-bus-cxl | 13 ++++++++
>  drivers/cxl/core/extent.c               | 58 +++++++++++++++++++++++++++++++++
>  2 files changed, 71 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> index 3a5ee88e551b..e97e6a73c960 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cxl
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -599,3 +599,16 @@ Description:
>  		See Documentation/ABI/stable/sysfs-devices-node. access0 provides
>  		the number to the closest initiator and access1 provides the
>  		number to the closest CPU.
> +
> +What:		/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/tag

I wonder consider an entry for each with their own descriptions, which seems to be the standard practice.

DJ

> +Date:		October, 2024
> +KernelVersion:	v6.12
> +Contact:	linux-cxl@xxxxxxxxxxxxxxx
> +Description:
> +		(RO) [For Dynamic Capacity regions only]  Extent offset and
> +		length within the region.  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.
> diff --git a/drivers/cxl/core/extent.c b/drivers/cxl/core/extent.c
> index 34456594cdc3..d7d526a51e2b 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 region_extent *region_extent = to_region_extent(dev);
> +
> +	return sysfs_emit(buf, "%#llx\n", region_extent->hpa_range.start);
> +}
> +static DEVICE_ATTR_RO(offset);
> +
> +static ssize_t length_show(struct device *dev, struct device_attribute *attr,
> +			   char *buf)
> +{
> +	struct region_extent *region_extent = to_region_extent(dev);
> +	u64 length = range_len(&region_extent->hpa_range);
> +
> +	return sysfs_emit(buf, "%#llx\n", length);
> +}
> +static DEVICE_ATTR_RO(length);
> +
> +static ssize_t tag_show(struct device *dev, struct device_attribute *attr,
> +			char *buf)
> +{
> +	struct region_extent *region_extent = to_region_extent(dev);
> +
> +	return sysfs_emit(buf, "%pUb\n", &region_extent->tag);
> +}
> +static DEVICE_ATTR_RO(tag);
> +
> +static struct attribute *region_extent_attrs[] = {
> +	&dev_attr_offset.attr,
> +	&dev_attr_length.attr,
> +	&dev_attr_tag.attr,
> +	NULL,
> +};
> +
> +static uuid_t empty_tag = { 0 };
> +
> +static umode_t region_extent_visible(struct kobject *kobj,
> +				     struct attribute *a, int n)
> +{
> +	struct device *dev = kobj_to_dev(kobj);
> +	struct region_extent *region_extent = to_region_extent(dev);
> +
> +	if (a == &dev_attr_tag.attr &&
> +	    uuid_equal(&region_extent->tag, &empty_tag))
> +		return 0;
> +
> +	return a->mode;
> +}
> +
> +static const struct attribute_group region_extent_attribute_group = {
> +	.attrs = region_extent_attrs,
> +	.is_visible = region_extent_visible,
> +};
> +
> +__ATTRIBUTE_GROUPS(region_extent_attribute);
> +
>  static void cxled_release_extent(struct cxl_endpoint_decoder *cxled,
>  				 struct cxled_extent *ed_extent)
>  {
> @@ -44,6 +101,7 @@ static void region_extent_release(struct device *dev)
>  static const struct device_type region_extent_type = {
>  	.name = "extent",
>  	.release = region_extent_release,
> +	.groups = region_extent_attribute_groups,
>  };
>  
>  bool is_region_extent(struct device *dev)
>