Add module parameter and configfs option for controlling the maximum size
of an IO for the emulated block device.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 drivers/block/rnull/configfs.rs |  5 +++++
 drivers/block/rnull/rnull.rs    | 10 +++++++++-
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/drivers/block/rnull/configfs.rs b/drivers/block/rnull/configfs.rs
index b449ac882d961..9eaace8b4257e 100644
--- a/drivers/block/rnull/configfs.rs
+++ b/drivers/block/rnull/configfs.rs
@@ -122,6 +122,7 @@ fn make_group(
                 zone_append_max_sectors: 26,
                 poll_queues: 27,
                 fua: 28,
+                max_sectors: 29,
             ],
         };
 
@@ -208,6 +209,7 @@ fn make_group(
                     requeue_inject,
                     #[cfg(CONFIG_BLK_DEV_RUST_NULL_FAULT_INJECTION)]
                     init_hctx_inject,
+                    max_sectors: 0,
                 }),
             }),
             default_groups,
@@ -290,6 +292,7 @@ struct DeviceConfigInner {
     requeue_inject: Arc<FaultConfig>,
     #[cfg(CONFIG_BLK_DEV_RUST_NULL_FAULT_INJECTION)]
     init_hctx_inject: Arc<FaultConfig>,
+    max_sectors: u32,
 }
 
 #[vtable]
@@ -347,6 +350,7 @@ fn store(this: &DeviceConfig, page: &[u8]) -> Result {
                 init_hctx_inject: guard.init_hctx_inject.clone(),
                 #[cfg(CONFIG_BLK_DEV_RUST_NULL_FAULT_INJECTION)]
                 timeout_inject: guard.timeout_inject.clone(),
+                max_sectors: guard.max_sectors,
             })?);
             guard.powered = true;
         } else if guard.powered && !power_op {
@@ -624,3 +628,4 @@ fn store(this: &DeviceConfig, page: &[u8]) -> Result {
     },
 }
 configfs_simple_bool_field!(DeviceConfig, 28, fua);
+configfs_simple_field!(DeviceConfig, 29, max_sectors, u32);
diff --git a/drivers/block/rnull/rnull.rs b/drivers/block/rnull/rnull.rs
index b2b089a657f12..495a810f4f4e1 100644
--- a/drivers/block/rnull/rnull.rs
+++ b/drivers/block/rnull/rnull.rs
@@ -206,6 +206,10 @@
             default: 1,
             description: "Enable/disable FUA support when cache_size is used. Default: 1 (true)",
         },
+        max_sectors: u32 {
+            default: 0,
+            description: "Maximum size of a command (in 512B sectors)",
+        },
     },
 }
 
@@ -282,6 +286,7 @@ fn init(_module: &'static ThisModule) -> impl PinInit<Self, Error> {
                     )?,
                     #[cfg(CONFIG_BLK_DEV_RUST_NULL_FAULT_INJECTION)]
                     timeout_inject: Arc::pin_init(FaultConfig::new(c"timeout_inject"), GFP_KERNEL)?,
+                    max_sectors: *module_parameters::max_sectors.value(),
                 })?;
                 disks.push(disk, GFP_KERNEL)?;
             }
@@ -336,6 +341,7 @@ struct NullBlkOptions<'a> {
     init_hctx_inject: Arc<FaultConfig>,
     #[cfg(CONFIG_BLK_DEV_RUST_NULL_FAULT_INJECTION)]
     timeout_inject: Arc<FaultConfig>,
+    max_sectors: u32,
 }
 
 static SHARED_TAG_SET: SetOnce<Arc<TagSet<NullBlkDevice>>> = SetOnce::new();
@@ -407,6 +413,7 @@ fn new(options: NullBlkOptions<'_>) -> Result<Arc<GenDisk<Self>>> {
             init_hctx_inject,
             #[cfg(CONFIG_BLK_DEV_RUST_NULL_FAULT_INJECTION)]
             timeout_inject,
+            max_sectors,
         } = options;
 
         let mut flags = mq::tag_set::Flags::default();
@@ -502,7 +509,8 @@ fn new(options: NullBlkOptions<'_>) -> Result<Arc<GenDisk<Self>>> {
             .physical_block_size(block_size_bytes)?
             .rotational(rotational)
             .write_cache(storage.cache_enabled())
-            .forced_unit_access(forced_unit_access && storage.cache_enabled());
+            .forced_unit_access(forced_unit_access && storage.cache_enabled())
+            .max_sectors(max_sectors);
 
         #[cfg(CONFIG_BLK_DEV_ZONED)]
         {

-- 
2.51.2