Add support for the badblocks_once feature, which automatically clears
bad blocks after they are encountered during I/O operations. This
matches the functionality in the C null_blk driver.

When badblocks_once is enabled:
- Bad blocks are checked during I/O requests as usual
- If a bad block is encountered, the I/O is marked as failed
- The bad block range is immediately cleared from the bad blocks table
- Subsequent I/O to the same sectors will succeed

This feature is useful for testing scenarios where bad blocks are
transient or where devices can recover from bad sectors after a single
access attempt.

The feature is configurable via the configfs badblocks_once attribute
and disabled by default, maintaining compatibility with existing
behavior.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 drivers/block/rnull/configfs.rs |  6 ++++++
 drivers/block/rnull/rnull.rs    | 21 +++++++++++++++------
 2 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/drivers/block/rnull/configfs.rs b/drivers/block/rnull/configfs.rs
index 4db3ba26c2d1..05229ba9173a 100644
--- a/drivers/block/rnull/configfs.rs
+++ b/drivers/block/rnull/configfs.rs
@@ -102,6 +102,7 @@ fn make_group(
                 discard: 10,
                 no_sched:11,
                 badblocks: 12,
+                badblocks_once: 13,
             ],
         };
 
@@ -125,6 +126,7 @@ fn make_group(
                     discard: false,
                     no_sched: false,
                     bad_blocks: Arc::pin_init(BadBlocks::new(false), GFP_KERNEL)?,
+                    bad_blocks_once: false,
                 }),
             }),
             core::iter::empty(),
@@ -195,6 +197,7 @@ struct DeviceConfigInner {
     discard: bool,
     no_sched: bool,
     bad_blocks: Arc<BadBlocks>,
+    bad_blocks_once: bool,
 }
 
 #[vtable]
@@ -231,6 +234,7 @@ fn store(this: &DeviceConfig, page: &[u8]) -> Result {
                 discard: guard.discard,
                 no_sched: guard.no_sched,
                 bad_blocks: guard.bad_blocks.clone(),
+                bad_blocks_once: guard.bad_blocks_once,
             })?);
             guard.powered = true;
         } else if guard.powered && !power_op {
@@ -383,3 +387,5 @@ fn store(this: &DeviceConfig, page: &[u8]) -> Result {
         Ok(())
     }
 }
+
+configfs_simple_bool_field!(DeviceConfig, 13, bad_blocks_once);
diff --git a/drivers/block/rnull/rnull.rs b/drivers/block/rnull/rnull.rs
index 90dbf318c2f8..5486eb6dd921 100644
--- a/drivers/block/rnull/rnull.rs
+++ b/drivers/block/rnull/rnull.rs
@@ -159,6 +159,7 @@ fn init(_module: &'static ThisModule) -> impl PinInit<Self, Error> {
                     discard: module_parameters::discard.value(),
                     no_sched: module_parameters::no_sched.value(),
                     bad_blocks: Arc::pin_init(BadBlocks::new(false), GFP_KERNEL)?,
+                    bad_blocks_once: false,
                 })?;
                 disks.push(disk, GFP_KERNEL)?;
             }
@@ -186,6 +187,7 @@ struct NullBlkOptions<'a> {
     discard: bool,
     no_sched: bool,
     bad_blocks: Arc<BadBlocks>,
+    bad_blocks_once: bool,
 }
 struct NullBlkDevice;
 
@@ -204,6 +206,7 @@ fn new(options: NullBlkOptions<'_>) -> Result<GenDisk<Self>> {
             discard,
             no_sched,
             bad_blocks,
+            bad_blocks_once,
         } = options;
 
         let mut flags = mq::tag_set::Flags::default();
@@ -246,6 +249,7 @@ fn new(options: NullBlkOptions<'_>) -> Result<GenDisk<Self>> {
                 memory_backed,
                 block_size: block_size.into(),
                 bad_blocks,
+                bad_blocks_once,
             }),
             GFP_KERNEL,
         )?;
@@ -416,6 +420,7 @@ struct QueueData {
     memory_backed: bool,
     block_size: u64,
     bad_blocks: Arc<BadBlocks>,
+    bad_blocks_once: bool,
 }
 
 #[pin_data]
@@ -465,12 +470,16 @@ fn queue_rq(
         if queue_data.bad_blocks.enabled() {
             let start = rq.sector();
             let end = start + u64::from(rq.sectors());
-            if !matches!(
-                queue_data.bad_blocks.check(start..end),
-                badblocks::BlockStatus::None
-            ) {
-                rq.data_ref().error.store(1, ordering::Relaxed);
-            }
+            match queue_data.bad_blocks.check(start..end) {
+                badblocks::BlockStatus::None => {}
+                badblocks::BlockStatus::Acknowledged(range)
+                | badblocks::BlockStatus::Unacknowledged(range) => {
+                    rq.data_ref().error.store(1, ordering::Relaxed);
+                    if queue_data.bad_blocks_once {
+                        queue_data.bad_blocks.set_good(range)?;
+                    }
+                }
+            };
         }
 
         // TODO: Skip IO if bad block.

-- 
2.51.2