[PATCH v2 33/83] block: rust: add `TagSet` private data support

[Andreas Hindborg]

From: Andreas Hindborg <a.hindborg@xxxxxxxxxxx>

C block device drivers can attach private data to a `struct
blk_mq_tag_set`. Add support for this feature for Rust block device
drivers via the `Operations::TagSetData` associated type.

The private data is passed to `TagSet::new` and is stored in the
`driver_data` field of the underlying `struct blk_mq_tag_set`. It is
released when the `TagSet` is dropped.

Signed-off-by: Andreas Hindborg <a.hindborg@xxxxxxxxxx>
---
 drivers/block/rnull/rnull.rs       |  3 ++-
 rust/kernel/block/mq.rs            |  6 ++++--
 rust/kernel/block/mq/operations.rs |  4 ++++
 rust/kernel/block/mq/tag_set.rs    | 26 ++++++++++++++++++++++----
 4 files changed, 32 insertions(+), 7 deletions(-)

diff --git a/drivers/block/rnull/rnull.rs b/drivers/block/rnull/rnull.rs
index be0b4bd25e53..ad26a4a8dbbe 100644
--- a/drivers/block/rnull/rnull.rs
+++ b/drivers/block/rnull/rnull.rs
@@ -240,7 +240,7 @@ fn new(options: NullBlkOptions<'_>) -> Result<GenDisk<Self>> {
         }
 
         let tagset = Arc::pin_init(
-            TagSet::new(submit_queues, 256, 1, numa_node, flags),
+            TagSet::new(submit_queues, (), 256, 1, numa_node, flags),
             GFP_KERNEL,
         )?;
 
@@ -533,6 +533,7 @@ fn align_down<T>(value: T, to: T) -> T
 impl Operations for NullBlkDevice {
     type QueueData = Pin<KBox<QueueData>>;
     type RequestData = Pdu;
+    type TagSetData = ();
 
     fn new_request_data() -> impl PinInit<Self::RequestData> {
         pin_init!(Pdu {
diff --git a/rust/kernel/block/mq.rs b/rust/kernel/block/mq.rs
index bac15b509d90..28cee0d60846 100644
--- a/rust/kernel/block/mq.rs
+++ b/rust/kernel/block/mq.rs
@@ -71,6 +71,7 @@
 //! impl Operations for MyBlkDevice {
 //!     type RequestData = ();
 //!     type QueueData = ();
+//!     type TagSetData = ();
 //!
 //!     fn new_request_data(
 //!     ) -> impl PinInit<()> {
@@ -94,8 +95,9 @@
 //!
 //! let tagset: Arc<TagSet<MyBlkDevice>> =
 //!     Arc::pin_init(
-//!         TagSet::new(1, 256, 1, NumaNode::NO_NODE, mq::tag_set::Flags::default()),
-//!         GFP_KERNEL)?;
+//!         TagSet::new(1, (), 256, 1, NumaNode::NO_NODE, mq::tag_set::Flags::default()),
+//!         GFP_KERNEL
+//!     )?;
 //! let mut disk = gen_disk::GenDiskBuilder::new()
 //!     .capacity_sectors(4096)
 //!     .build(fmt!("myblk"), tagset, ())?;
diff --git a/rust/kernel/block/mq/operations.rs b/rust/kernel/block/mq/operations.rs
index c49ca2e8bbb2..093bb21fa1b2 100644
--- a/rust/kernel/block/mq/operations.rs
+++ b/rust/kernel/block/mq/operations.rs
@@ -63,6 +63,10 @@ pub trait Operations: Sized {
     /// the `GenDisk` associated with this `Operations` implementation.
     type QueueData: ForeignOwnable + Sync;
 
+    /// Data associated with a `TagSet`. This is stored as a pointer in `struct
+    /// blk_mq_tag_set`.
+    type TagSetData: ForeignOwnable + Sync;
+
     /// Called by the kernel to get an initializer for a `Pin<&mut RequestData>`.
     fn new_request_data() -> impl PinInit<Self::RequestData>;
 
diff --git a/rust/kernel/block/mq/tag_set.rs b/rust/kernel/block/mq/tag_set.rs
index d6d104adf4aa..bfb8f8af4ee1 100644
--- a/rust/kernel/block/mq/tag_set.rs
+++ b/rust/kernel/block/mq/tag_set.rs
@@ -19,7 +19,10 @@
         Result, //
     },
     prelude::*,
-    types::Opaque,
+    types::{
+        ForeignOwnable,
+        Opaque, //
+    },
 };
 use core::{
     convert::TryInto,
@@ -56,6 +59,7 @@ impl<T: Operations> TagSet<T> {
     /// Try to create a new tag set
     pub fn new(
         nr_hw_queues: u32,
+        tagset_data: T::TagSetData,
         num_tags: u32,
         num_maps: u32,
         numa_node: NumaNode,
@@ -73,7 +77,7 @@ pub fn new(
                     queue_depth: num_tags,
                     cmd_size,
                     flags: flags.into(),
-                    driver_data: core::ptr::null_mut::<c_void>(),
+                    driver_data: tagset_data.into_foreign(),
                     nr_maps: num_maps,
                     ..tag_set
                 }
@@ -86,7 +90,14 @@ pub fn new(
                 // SAFETY: we do not move out of `tag_set`.
                 let tag_set: &mut Opaque<_> = unsafe { Pin::get_unchecked_mut(tag_set) };
                 // SAFETY: `tag_set` is a reference to an initialized `blk_mq_tag_set`.
-                error::to_result( unsafe { bindings::blk_mq_alloc_tag_set(tag_set.get())})
+                let status = error::to_result(
+                    unsafe { bindings::blk_mq_alloc_tag_set(tag_set.get())}
+                );
+                if status.is_err() {
+                    // SAFETY: We created `driver_data` above with `into_foreign`
+                    unsafe { T::TagSetData::from_foreign((*tag_set.get()).driver_data) };
+                }
+                status
             }),
             _p: PhantomData,
         })
@@ -102,7 +113,14 @@ pub(crate) fn raw_tag_set(&self) -> *mut bindings::blk_mq_tag_set {
 impl<T: Operations> PinnedDrop for TagSet<T> {
     fn drop(self: Pin<&mut Self>) {
         // SAFETY: By type invariant `inner` is valid and has been properly
-        // initialized during construction.
+        // initialised during construction.
+        let tagset_data = unsafe { (*self.inner.get()).driver_data };
+
+        // SAFETY: `inner` is valid and has been properly initialised during construction.
         unsafe { bindings::blk_mq_free_tag_set(self.inner.get()) };
+
+        // SAFETY: `tagset_data` was created by a call to
+        // `ForeignOwnable::into_foreign` in `TagSet::try_new()`
+        unsafe { T::TagSetData::from_foreign(tagset_data) };
     }
 }

-- 
2.51.2