Add support for blocking queue mode via the `blocking` configfs
attribute. When enabled, the tag set is created with the
`BLK_MQ_F_BLOCKING` flag.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 drivers/block/rnull/configfs.rs | 7 ++++++-
 drivers/block/rnull/rnull.rs    | 9 ++++++++-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/drivers/block/rnull/configfs.rs b/drivers/block/rnull/configfs.rs
index 59217d75f46b..5e6bcf9d31d8 100644
--- a/drivers/block/rnull/configfs.rs
+++ b/drivers/block/rnull/configfs.rs
@@ -69,7 +69,7 @@ impl AttributeOperations<0> for Config {
         let mut writer = kernel::str::Formatter::new(page);
         writer.write_str(
             "blocksize,size,rotational,irqmode,completion_nsec,memory_backed,\
-             submit_queues,use_per_node_hctx\n",
+             submit_queues,use_per_node_hctx,discard,blocking\n",
         )?;
         Ok(writer.bytes_written())
     }
@@ -105,6 +105,7 @@ fn make_group(
                 badblocks_partial_io: 14,
                 cache_size_mib: 15,
                 mbps: 16,
+                blocking: 17,
             ],
         };
 
@@ -137,6 +138,7 @@ fn make_group(
                     )?,
                     cache_size_mib: 0,
                     mbps: 0,
+                    blocking: false,
                 }),
             }),
             core::iter::empty(),
@@ -212,6 +214,7 @@ struct DeviceConfigInner {
     cache_size_mib: u64,
     disk_storage: Arc<DiskStorage>,
     mbps: u32,
+    blocking: bool,
 }
 
 #[vtable]
@@ -252,6 +255,7 @@ fn store(this: &DeviceConfig, page: &[u8]) -> Result {
                 bad_blocks_partial_io: guard.bad_blocks_partial_io,
                 storage: guard.disk_storage.clone(),
                 bandwidth_limit: u64::from(guard.mbps) * 2u64.pow(20),
+                blocking: guard.blocking,
             })?);
             guard.powered = true;
         } else if guard.powered && !power_op {
@@ -422,3 +426,4 @@ fn store(this: &DeviceConfig, page: &[u8]) -> Result {
 );
 
 configfs_simple_field!(DeviceConfig, 16, mbps, u32);
+configfs_simple_bool_field!(DeviceConfig, 17, blocking);
diff --git a/drivers/block/rnull/rnull.rs b/drivers/block/rnull/rnull.rs
index 1dda8d717b95..181fce551a91 100644
--- a/drivers/block/rnull/rnull.rs
+++ b/drivers/block/rnull/rnull.rs
@@ -139,6 +139,10 @@
             default: 0,
             description: "Max bandwidth in MiB/s. 0 means no limit.",
         },
+        blocking: bool {
+            default: false,
+            description: "Register as a blocking blk-mq driver device",
+        },
     },
 }
 
@@ -185,6 +189,7 @@ fn init(_module: &'static ThisModule) -> impl PinInit<Self, Error> {
                     bad_blocks_partial_io: false,
                     storage: Arc::pin_init(DiskStorage::new(0, block_size as usize), GFP_KERNEL)?,
                     bandwidth_limit: u64::from(module_parameters::mbps.value()) * 2u64.pow(20),
+                    blocking: module_parameters::blocking.value(),
                 })?;
                 disks.push(disk, GFP_KERNEL)?;
             }
@@ -216,6 +221,7 @@ struct NullBlkOptions<'a> {
     bad_blocks_partial_io: bool,
     storage: Arc<DiskStorage>,
     bandwidth_limit: u64,
+    blocking: bool,
 }
 
 #[pin_data]
@@ -258,11 +264,12 @@ fn new(options: NullBlkOptions<'_>) -> Result<Arc<GenDisk<Self>>> {
             bad_blocks_partial_io,
             storage,
             bandwidth_limit,
+            blocking,
         } = options;
 
         let mut flags = mq::tag_set::Flags::default();
 
-        if memory_backed {
+        if blocking || memory_backed {
             flags |= mq::tag_set::Flag::Blocking;
         }
 

-- 
2.51.2