Add `hw_queue_count()` to query the number of hardware queues and
`data()` to borrow the private tag set data associated with a `TagSet`.

Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/kernel/block/mq/tag_set.rs | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/rust/kernel/block/mq/tag_set.rs b/rust/kernel/block/mq/tag_set.rs
index e6edc5bc39312..4d00979a83dbd 100644
--- a/rust/kernel/block/mq/tag_set.rs
+++ b/rust/kernel/block/mq/tag_set.rs
@@ -4,8 +4,6 @@
 //!
 //! C header: [`include/linux/blk-mq.h`](srctree/include/linux/blk-mq.h)
 
-use core::pin::Pin;
-
 use crate::{
     bindings,
     block::mq::{operations::OperationsVTable, request::RequestDataWrapper, Operations},
@@ -13,7 +11,7 @@
     try_pin_init,
     types::{ForeignOwnable, Opaque},
 };
-use core::{convert::TryInto, marker::PhantomData};
+use core::{convert::TryInto, marker::PhantomData, pin::Pin};
 use pin_init::{pin_data, pinned_drop, PinInit};
 
 mod flags;
@@ -137,6 +135,22 @@ pub fn update_maps(self: Pin<&mut Self>, mut cb: impl FnMut(QueueMap)) -> Result
 
         Ok(())
     }
+
+    /// Return the number of hardware queues for this tag set.
+    pub fn hw_queue_count(&self) -> u32 {
+        // SAFETY: By type invariant, `self.inner` is valid.
+        unsafe { (*self.inner.get()).nr_hw_queues }
+    }
+
+    /// Borrow the [`T::TagSetData`] associated with this tag set.
+    pub fn data(&self) -> <T::TagSetData as ForeignOwnable>::Borrowed<'_> {
+        // SAFETY: By type invariant, `self.inner` is valid.
+        let ptr = unsafe { (*self.inner.get()).driver_data };
+
+        // SAFETY: `ptr` was created by `into_foreign` during initialization and the target is not
+        // converted back with `from_foreign` while `&self` is live.
+        unsafe { T::TagSetData::borrow(ptr) }
+    }
 }
 
 #[pinned_drop]

-- 
2.51.2