Add a configfs attribute to specify the NUMA node for rnull tag set
and CPU map allocations. This allows testing NUMA-aware block device
behavior and optimizing memory placement for specific hardware
configurations.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 drivers/block/rnull/configfs.rs | 19 +++++++++++++++++++
 drivers/block/rnull/rnull.rs    | 18 ++++++++++++++++--
 2 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/drivers/block/rnull/configfs.rs b/drivers/block/rnull/configfs.rs
index b05bfc23090c2..fe00617d2b679 100644
--- a/drivers/block/rnull/configfs.rs
+++ b/drivers/block/rnull/configfs.rs
@@ -5,6 +5,7 @@
     THIS_MODULE, //
 };
 use kernel::{
+    bindings,
     block::mq::gen_disk::{
         GenDisk,
         GenDiskBuilder, //
@@ -92,6 +93,7 @@ fn make_group(
                 memory_backed: 6,
                 submit_queues: 7,
                 use_per_node_hctx: 8,
+                home_node: 9,
             ],
         };
 
@@ -111,6 +113,7 @@ fn make_group(
                     name: name.try_into()?,
                     memory_backed: false,
                     submit_queues: 1,
+                    home_node: bindings::NUMA_NO_NODE,
                 }),
             }),
             core::iter::empty(),
@@ -167,6 +170,7 @@ struct DeviceConfigInner {
     disk: Option<GenDisk<NullBlkDevice>>,
     memory_backed: bool,
     submit_queues: u32,
+    home_node: i32,
 }
 
 #[vtable]
@@ -199,6 +203,7 @@ fn store(this: &DeviceConfig, page: &[u8]) -> Result {
                 completion_time: guard.completion_time,
                 memory_backed: guard.memory_backed,
                 submit_queues: guard.submit_queues,
+                home_node: guard.home_node,
             })?);
             guard.powered = true;
         } else if guard.powered && !power_op {
@@ -302,3 +307,17 @@ fn store(this: &DeviceConfig, page: &[u8]) -> Result {
         Ok(())
     })
 );
+
+configfs_simple_field!(
+    DeviceConfig,
+    9,
+    home_node,
+    i32,
+    check | value | {
+        if value == 0 || value >= kernel::num_online_nodes().try_into()? {
+            Err(kernel::error::code::EINVAL)
+        } else {
+            Ok(())
+        }
+    }
+);
diff --git a/drivers/block/rnull/rnull.rs b/drivers/block/rnull/rnull.rs
index 278f75d886fd9..fb3ce272d5bec 100644
--- a/drivers/block/rnull/rnull.rs
+++ b/drivers/block/rnull/rnull.rs
@@ -20,7 +20,10 @@
             TagSet, //
         },
     },
-    error::Result,
+    error::{
+        code,
+        Result, //
+    },
     new_mutex,
     new_xarray,
     page::SafePage,
@@ -95,6 +98,10 @@
             description:
         "Use per-node allocation for hardware context queues, 0-false, 1-true. Default: 0-false",
         },
+        home_node: i32 {
+            default: -1,
+            description: "Home node for the device. Default: -1 (no node)",
+        },
     },
 }
 
@@ -131,6 +138,7 @@ fn init(_module: &'static ThisModule) -> impl PinInit<Self, Error> {
                     completion_time: Delta::from_nanos(completion_time),
                     memory_backed: *module_parameters::memory_backed.value() != 0,
                     submit_queues,
+                    home_node: *module_parameters::home_node.value(),
                 })?;
                 disks.push(disk, GFP_KERNEL)?;
             }
@@ -154,6 +162,7 @@ struct NullBlkOptions<'a> {
     completion_time: Delta,
     memory_backed: bool,
     submit_queues: u32,
+    home_node: i32,
 }
 struct NullBlkDevice;
 
@@ -168,6 +177,7 @@ fn new(options: NullBlkOptions<'_>) -> Result<GenDisk<Self>> {
             completion_time,
             memory_backed,
             submit_queues,
+            home_node,
         } = options;
 
         let flags = if memory_backed {
@@ -176,8 +186,12 @@ fn new(options: NullBlkOptions<'_>) -> Result<GenDisk<Self>> {
             mq::tag_set::Flags::default()
         };
 
+        if home_node > kernel::num_online_nodes().try_into()? {
+            return Err(code::EINVAL);
+        }
+
         let tagset = Arc::pin_init(
-            TagSet::new(submit_queues, 256, 1, bindings::NUMA_NO_NODE, flags),
+            TagSet::new(submit_queues, 256, 1, home_node, flags),
             GFP_KERNEL,
         )?;
 

-- 
2.51.2