linux-kernel - [PATCH] block: rnull: Initialize the module in place

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Message-Id: <20241204-rnull_in_place-v1-1-efe3eafac9fb@dugarreau.fr>
Date: Wed, 04 Dec 2024 09:38:39 +0100
From: Benoît du Garreau <benoit@...arreau.fr>
To: Andreas Hindborg <a.hindborg@...nel.org>, 
 Boqun Feng <boqun.feng@...il.com>, Jens Axboe <axboe@...nel.dk>
Cc: linux-block@...r.kernel.org, rust-for-linux@...r.kernel.org, 
 linux-kernel@...r.kernel.org, 
 Benoît du Garreau <benoit@...arreau.fr>
Subject: [PATCH] block: rnull: Initialize the module in place

Using `InPlaceModule` avoids an allocation and an indirection.

Signed-off-by: Benoît du Garreau <benoit@...arreau.fr>
---
 drivers/block/rnull.rs | 30 ++++++++++++++++++------------
 1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/drivers/block/rnull.rs b/drivers/block/rnull.rs
index 5de7223beb4d5b4224010c86fca826967a019c27..6cdd2589c4621369cd57af66a2b817889321ed15 100644
--- a/drivers/block/rnull.rs
+++ b/drivers/block/rnull.rs
@@ -31,25 +31,31 @@
     license: "GPL v2",
 }
 
+#[pin_data]
 struct NullBlkModule {
-    _disk: Pin<KBox<Mutex<GenDisk<NullBlkDevice>>>>,
+    #[pin]
+    _disk: Mutex<GenDisk<NullBlkDevice>>,
 }
 
-impl kernel::Module for NullBlkModule {
-    fn init(_module: &'static ThisModule) -> Result<Self> {
+impl kernel::InPlaceModule for NullBlkModule {
+    fn init(_module: &'static ThisModule) -> impl PinInit<Self, Error> {
         pr_info!("Rust null_blk loaded\n");
-        let tagset = Arc::pin_init(TagSet::new(1, 256, 1), flags::GFP_KERNEL)?;
 
-        let disk = gen_disk::GenDiskBuilder::new()
-            .capacity_sectors(4096 << 11)
-            .logical_block_size(4096)?
-            .physical_block_size(4096)?
-            .rotational(false)
-            .build(format_args!("rnullb{}", 0), tagset)?;
+        // Use a immediately-called closure as a stable `try` block
+        let disk = /* try */ (|| {
+            let tagset = Arc::pin_init(TagSet::new(1, 256, 1), flags::GFP_KERNEL)?;
 
-        let disk = KBox::pin_init(new_mutex!(disk, "nullb:disk"), flags::GFP_KERNEL)?;
+            gen_disk::GenDiskBuilder::new()
+                .capacity_sectors(4096 << 11)
+                .logical_block_size(4096)?
+                .physical_block_size(4096)?
+                .rotational(false)
+                .build(format_args!("rnullb{}", 0), tagset)
+        })();
 
-        Ok(Self { _disk: disk })
+        try_pin_init!(Self {
+            _disk <- new_mutex!(disk?, "nullb:disk"),
+        })
     }
 }
 

---
base-commit: 4d6f8ba6e0a7b0627b4a559747948ee0d6797a3a
change-id: 20241203-rnull_in_place-5e0b73d8300c

Best regards,
-- 
Benoît du Garreau <benoit@...arreau.fr>