Add a new configfs boolean attribute named blocking.

Advertise blocking in the rnull features list.

On power-on, map blocking=1 to TagSetFlags::BLOCKING.

Create the tag set with TagSet::new_with_flags().

Keep default blocking=0 to preserve existing behavior.

Like other parameters, blocking writes return -EBUSY while powered on.

Validated with LLVM=-15 out-of-tree builds and QEMU runtime tests.

Signed-off-by: Wenzhao Liao <wenzhaoliao@ruc.edu.cn>
---
 drivers/block/rnull/configfs.rs | 32 +++++++++++++++++++++++++++++++-
 drivers/block/rnull/rnull.rs    | 11 +++++++++--
 2 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/drivers/block/rnull/configfs.rs b/drivers/block/rnull/configfs.rs
index 7c2eb5c0b722..a9d46a511340 100644
--- a/drivers/block/rnull/configfs.rs
+++ b/drivers/block/rnull/configfs.rs
@@ -35,7 +35,7 @@ impl AttributeOperations<0> for Config {
 
     fn show(_this: &Config, page: &mut [u8; PAGE_SIZE]) -> Result<usize> {
         let mut writer = kernel::str::Formatter::new(page);
-        writer.write_str("blocksize,size,rotational,irqmode\n")?;
+        writer.write_str("blocksize,size,rotational,irqmode,blocking\n")?;
         Ok(writer.bytes_written())
     }
 }
@@ -58,6 +58,7 @@ fn make_group(
                 rotational: 2,
                 size: 3,
                 irqmode: 4,
+                blocking: 5,
             ],
         };
 
@@ -73,6 +74,7 @@ fn make_group(
                     disk: None,
                     capacity_mib: 4096,
                     irq_mode: IRQMode::None,
+                    blocking: false,
                     name: name.try_into()?,
                 }),
             }),
@@ -122,6 +124,7 @@ struct DeviceConfigInner {
     rotational: bool,
     capacity_mib: u64,
     irq_mode: IRQMode,
+    blocking: bool,
     disk: Option<GenDisk<NullBlkDevice>>,
 }
 
@@ -152,6 +155,7 @@ fn store(this: &DeviceConfig, page: &[u8]) -> Result {
                 guard.rotational,
                 guard.capacity_mib,
                 guard.irq_mode,
+                guard.blocking,
             )?);
             guard.powered = true;
         } else if guard.powered && !power_op {
@@ -259,3 +263,29 @@ fn store(this: &DeviceConfig, page: &[u8]) -> Result {
         Ok(())
     }
 }
+
+#[vtable]
+impl configfs::AttributeOperations<5> for DeviceConfig {
+    type Data = DeviceConfig;
+
+    fn show(this: &DeviceConfig, page: &mut [u8; PAGE_SIZE]) -> Result<usize> {
+        let mut writer = kernel::str::Formatter::new(page);
+
+        if this.data.lock().blocking {
+            writer.write_str("1\n")?;
+        } else {
+            writer.write_str("0\n")?;
+        }
+
+        Ok(writer.bytes_written())
+    }
+
+    fn store(this: &DeviceConfig, page: &[u8]) -> Result {
+        if this.data.lock().powered {
+            return Err(EBUSY);
+        }
+
+        this.data.lock().blocking = kstrtobool_bytes(page)?;
+        Ok(())
+    }
+}
diff --git a/drivers/block/rnull/rnull.rs b/drivers/block/rnull/rnull.rs
index 0ca8715febe8..d7ebd504d8df 100644
--- a/drivers/block/rnull/rnull.rs
+++ b/drivers/block/rnull/rnull.rs
@@ -11,7 +11,7 @@
         mq::{
             self,
             gen_disk::{self, GenDisk},
-            Operations, TagSet,
+            Operations, TagSet, TagSetFlags,
         },
     },
     prelude::*,
@@ -51,8 +51,15 @@ fn new(
         rotational: bool,
         capacity_mib: u64,
         irq_mode: IRQMode,
+        blocking: bool,
     ) -> Result<GenDisk<Self>> {
-        let tagset = Arc::pin_init(TagSet::new(1, 256, 1), GFP_KERNEL)?;
+        let flags = if blocking {
+            TagSetFlags::BLOCKING
+        } else {
+            TagSetFlags::empty()
+        };
+
+        let tagset = Arc::pin_init(TagSet::new_with_flags(1, 256, 1, flags), GFP_KERNEL)?;
 
         let queue_data = Box::new(QueueData { irq_mode }, GFP_KERNEL)?;
 
-- 
2.34.1