Add support for configuring the maximum hardware discard sectors
through GenDiskBuilder. This allows block devices to specify their
discard/trim capabilities.

Setting this value to 0 (the default) indicates that discard is not
supported by the device. Non-zero values specify the maximum number
of sectors that can be discarded in a single operation.

Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org>
---
 rust/kernel/block/mq/gen_disk.rs | 34 ++++++++++++++++++++++++++++++----
 1 file changed, 30 insertions(+), 4 deletions(-)

diff --git a/rust/kernel/block/mq/gen_disk.rs b/rust/kernel/block/mq/gen_disk.rs
index b36d24382cc3..2b204b0ed49a 100644
--- a/rust/kernel/block/mq/gen_disk.rs
+++ b/rust/kernel/block/mq/gen_disk.rs
@@ -7,14 +7,27 @@
 
 use crate::{
     bindings,
-    block::mq::{Operations, TagSet},
-    error::{self, from_err_ptr, Result},
-    fmt::{self, Write},
+    block::mq::{
+        Operations,
+        TagSet, //
+    },
+    error::{
+        self,
+        from_err_ptr,
+        Result, //
+    },
+    fmt::{
+        self,
+        Write, //
+    },
     prelude::*,
     static_lock_class,
     str::NullTerminatedFormatter,
     sync::Arc,
-    types::{ForeignOwnable, ScopeGuard},
+    types::{
+        ForeignOwnable,
+        ScopeGuard, //
+    },
 };
 
 /// A builder for [`GenDisk`].
@@ -25,6 +38,7 @@ pub struct GenDiskBuilder {
     logical_block_size: u32,
     physical_block_size: u32,
     capacity_sectors: u64,
+    max_hw_discard_sectors: u32,
 }
 
 impl Default for GenDiskBuilder {
@@ -34,6 +48,7 @@ fn default() -> Self {
             logical_block_size: bindings::PAGE_SIZE as u32,
             physical_block_size: bindings::PAGE_SIZE as u32,
             capacity_sectors: 0,
+            max_hw_discard_sectors: 0,
         }
     }
 }
@@ -94,6 +109,16 @@ pub fn capacity_sectors(mut self, capacity: u64) -> Self {
         self
     }
 
+    /// Set the maximum amount of sectors the underlying hardware device can
+    /// discard/trim in a single operation.
+    ///
+    /// Setting 0 (default) here will cause the disk to report discard not
+    /// supported.
+    pub fn max_hw_discard_sectors(mut self, max_hw_discard_sectors: u32) -> Self {
+        self.max_hw_discard_sectors = max_hw_discard_sectors;
+        self
+    }
+
     /// Build a new `GenDisk` and add it to the VFS.
     pub fn build<T: Operations>(
         self,
@@ -111,6 +136,7 @@ pub fn build<T: Operations>(
 
         lim.logical_block_size = self.logical_block_size;
         lim.physical_block_size = self.physical_block_size;
+        lim.max_hw_discard_sectors = self.max_hw_discard_sectors;
         if self.rotational {
             lim.features = bindings::BLK_FEAT_ROTATIONAL;
         }

-- 
2.51.2