Add support for `TagSet` flags by introducing a `Flags` type and adding
a flags parameter to `TagSet::new`. This allows configuring tagset
behavior such as blocking vs non-blocking operation.

The Flags type supports bitwise operations and provides values like
`Blocking` for common use cases. The module documentation example is
updated to demonstrate the new API.

For now, only a single flag is added.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 drivers/block/rnull/rnull.rs          |  5 ++++-
 rust/kernel/block/mq.rs               |  6 +++---
 rust/kernel/block/mq/tag_set.rs       | 13 ++++++++++---
 rust/kernel/block/mq/tag_set/flags.rs | 21 +++++++++++++++++++++
 4 files changed, 38 insertions(+), 7 deletions(-)

diff --git a/drivers/block/rnull/rnull.rs b/drivers/block/rnull/rnull.rs
index 3e7a47e6d0e5..746ddadd11f0 100644
--- a/drivers/block/rnull/rnull.rs
+++ b/drivers/block/rnull/rnull.rs
@@ -128,7 +128,10 @@ fn new(
         irq_mode: IRQMode,
         completion_time: Delta,
     ) -> Result<GenDisk<Self>> {
-        let tagset = Arc::pin_init(TagSet::new(1, 256, 1), GFP_KERNEL)?;
+        let tagset = Arc::pin_init(
+            TagSet::new(1, 256, 1, mq::tag_set::Flags::default()),
+            GFP_KERNEL,
+        )?;
 
         let queue_data = Box::new(
             QueueData {
diff --git a/rust/kernel/block/mq.rs b/rust/kernel/block/mq.rs
index 23660817df29..e556b3bb1191 100644
--- a/rust/kernel/block/mq.rs
+++ b/rust/kernel/block/mq.rs
@@ -57,7 +57,7 @@
 //!
 //! ```rust
 //! use kernel::{
-//!     block::mq::*,
+//!     block::mq::{self, *},
 //!     new_mutex,
 //!     prelude::*,
 //!     sync::{aref::ARef, Arc, Mutex},
@@ -92,7 +92,7 @@
 //! }
 //!
 //! let tagset: Arc<TagSet<MyBlkDevice>> =
-//!     Arc::pin_init(TagSet::new(1, 256, 1), GFP_KERNEL)?;
+//!     Arc::pin_init(TagSet::new(1, 256, 1, mq::tag_set::Flags::default()), GFP_KERNEL)?;
 //! let mut disk = gen_disk::GenDiskBuilder::new()
 //!     .capacity_sectors(4096)
 //!     .build(fmt!("myblk"), tagset, ())?;
@@ -103,7 +103,7 @@
 pub mod gen_disk;
 mod operations;
 mod request;
-mod tag_set;
+pub mod tag_set;
 
 pub use operations::Operations;
 pub use request::{
diff --git a/rust/kernel/block/mq/tag_set.rs b/rust/kernel/block/mq/tag_set.rs
index ec5cac48b83f..5b1a5bcc978d 100644
--- a/rust/kernel/block/mq/tag_set.rs
+++ b/rust/kernel/block/mq/tag_set.rs
@@ -17,7 +17,7 @@
         self,
         Result, //
     },
-    prelude::try_pin_init,
+    prelude::*,
     types::Opaque,
 };
 use core::{
@@ -30,6 +30,12 @@
     PinInit, //
 };
 
+mod flags;
+pub use flags::{
+    Flag,
+    Flags, //
+};
+
 /// A wrapper for the C `struct blk_mq_tag_set`.
 ///
 /// `struct blk_mq_tag_set` contains a `struct list_head` and so must be pinned.
@@ -51,6 +57,7 @@ pub fn new(
         nr_hw_queues: u32,
         num_tags: u32,
         num_maps: u32,
+        flags: Flags,
     ) -> impl PinInit<Self, error::Error> {
         let tag_set: bindings::blk_mq_tag_set = pin_init::zeroed();
         let tag_set: Result<_> = size_of::<RequestDataWrapper<T>>()
@@ -63,8 +70,8 @@ pub fn new(
                     numa_node: bindings::NUMA_NO_NODE,
                     queue_depth: num_tags,
                     cmd_size,
-                    flags: 0,
-                    driver_data: core::ptr::null_mut::<crate::ffi::c_void>(),
+                    flags: flags.into(),
+                    driver_data: core::ptr::null_mut::<c_void>(),
                     nr_maps: num_maps,
                     ..tag_set
                 }
diff --git a/rust/kernel/block/mq/tag_set/flags.rs b/rust/kernel/block/mq/tag_set/flags.rs
new file mode 100644
index 000000000000..b7eaccd200a2
--- /dev/null
+++ b/rust/kernel/block/mq/tag_set/flags.rs
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+
+use crate::{
+    bindings,
+    impl_flags, //
+};
+
+impl_flags! {
+    /// Flags to be used when creating [`super::TagSet`] objects.
+    #[derive(Debug, Clone, Default, Copy, PartialEq, Eq)]
+    pub struct Flags(u32);
+
+    /// Allowed values for [`Flags`].
+    #[derive(Debug, Clone, Copy, PartialEq, Eq)]
+    pub enum Flag {
+        /// Indicate that the queues associated with this tag set might sleep when
+        /// processing IO. When this flag is not set, IO is processed in atomic
+        /// context. When this flag is set, IO is processed in process context.
+        Blocking = bindings::BLK_MQ_F_BLOCKING,
+    }
+}

-- 
2.51.2