Introduce a read-write 'uuid' sysfs entry at /sys/bus/dax/devices/daxX.Y/ with stubbed handlers: show returns the null uuid and store returns -EOPNOTSUPP. A follow-on patch wires both directions to dax_resource tracking.
Document the attribute in the dax sysfs ABI. Signed-off-by: Anisa Su <[email protected]> --- Changes: - uuid_show() emits the null uuid ("%pUb" of uuid_null) instead of "0". - ABI: describe the no-uuid read value as a null uuid instead of "0"; bump Date to June, 2026 and KernelVersion to v7.3. --- Documentation/ABI/testing/sysfs-bus-dax | 18 ++++++++++++++++++ drivers/dax/bus.c | 14 ++++++++++++++ 2 files changed, 32 insertions(+) diff --git a/Documentation/ABI/testing/sysfs-bus-dax b/Documentation/ABI/testing/sysfs-bus-dax index b34266bfae49..3219c09dea01 100644 --- a/Documentation/ABI/testing/sysfs-bus-dax +++ b/Documentation/ABI/testing/sysfs-bus-dax @@ -59,6 +59,24 @@ Description: backing device for this dax device, emit the CPU node affinity for this device. +What: /sys/bus/dax/devices/daxX.Y/uuid +Date: June, 2026 +KernelVersion: v7.3 +Contact: [email protected] +Description: + (RW) On read, reports the uuid identifying the capacity + backing this dax device. A null uuid (all-zeroes) indicates + that the device has no associated uuid — either it is not + backed by DCD capacity, or the backing extents are untagged. + + Writes are accepted only on dax devices in sparse (DCD) + regions; writes to non-sparse devices return -EOPNOTSUPP. + Writing a non-null uuid claims every dax_resource in the + parent region whose tag matches the written uuid, consuming + any available capacity in each matching resource. Writing + "0" is shorthand for the null uuid and claims a single + untagged dax_resource. + What: /sys/bus/dax/devices/daxX.Y/target_node Date: February, 2019 KernelVersion: v5.1 diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c index ffa6b303fc9b..f61309a6f934 100644 --- a/drivers/dax/bus.c +++ b/drivers/dax/bus.c @@ -1573,6 +1573,19 @@ static ssize_t numa_node_show(struct device *dev, } static DEVICE_ATTR_RO(numa_node); +static ssize_t uuid_show(struct device *dev, + struct device_attribute *attr, char *buf) +{ + return sysfs_emit(buf, "%pUb\n", &uuid_null); +} + +static ssize_t uuid_store(struct device *dev, struct device_attribute *attr, + const char *buf, size_t len) +{ + return -EOPNOTSUPP; +} +static DEVICE_ATTR_RW(uuid); + static ssize_t memmap_on_memory_show(struct device *dev, struct device_attribute *attr, char *buf) { @@ -1644,6 +1657,7 @@ static struct attribute *dev_dax_attributes[] = { &dev_attr_resource.attr, &dev_attr_numa_node.attr, &dev_attr_memmap_on_memory.attr, + &dev_attr_uuid.attr, NULL, }; -- 2.43.0
