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rust: add a sample alloc usage

PATCH In review Hui Zhu 3 participants 4 messages Jul 17, 2025 – Jul 24, 2025 Rust

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Hui Zhu

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#0 lore raw

PATCH v2 1/1 rust: add a sample alloc usage

From: Hui Zhu <[email protected]>

Add a sample to the samples memory alloc usage.
It will samples the usage of VBox and KVec.

It also includes a test for allocating alignments larger than PAGE_SIZE using VBox.
Since this feature is currently unsupported, it will report errors even when successful.

Changelog:
v2:
According to the comments of Danilo, updated the commit to samples the usage of VBox and KVec.

Co-developed-by Geliang Tang <[email protected]>
Signed-off-by Geliang Tang <[email protected]>
Signed-off-by Hui Zhu <[email protected]>
---
 samples/rust/Kconfig       | 10 +++++
 samples/rust/Makefile      |  1 +
 samples/rust/rust_alloc.rs | 88 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 99 insertions(+)
 create mode 100644 samples/rust/rust_alloc.rs
samples/rust/Kconfig +10 -0
index 7f7371a004ee..03a86f819768 100644
@@ -105,6 +105,16 @@ config SAMPLE_RUST_DRIVER_AUXILIARY
 
 	  If unsure, say N.
 
+config SAMPLE_RUST_ALLOC
+	tristate "Alloc Test Driver"
+	help
+	  This option builds the Rust alloc Test driver sample.
+
+	  To compile this as a module, choose M here:
+	  the module will be called rust_alloc.
+
+	  If unsure, say N.
+
 config SAMPLE_RUST_HOSTPROGS
 	bool "Host programs"
 	help
samples/rust/Makefile +1 -0
index bd2faad63b4f..7c3e68d9ada5 100644
@@ -10,6 +10,7 @@ obj-$(CONFIG_SAMPLE_RUST_DRIVER_PLATFORM)	+= rust_driver_platform.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_FAUX)		+= rust_driver_faux.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_AUXILIARY)	+= rust_driver_auxiliary.o
 obj-$(CONFIG_SAMPLE_RUST_CONFIGFS)		+= rust_configfs.o
+obj-$(CONFIG_SAMPLE_RUST_ALLOC)		+= rust_alloc.o
 
 rust_print-y := rust_print_main.o rust_print_events.o
samples/rust/rust_alloc.rs new file +88 -0

88 lines not on this page · raw message

Signature · 1 line
2.43.0
reviewer
#1 lore raw

(Cc: Lorenzo, Vlastimil, Liam, Uladzislau)

samples/rust/Makefile obj-$(CONFIG_SAMPLE_RUST_DRIVER_PLATFORM) += rust_driver_platform.o · line 13

Quoted 9 lines · Hui Zhu
samples/rust/Makefile +1 -0
index bd2faad63b4f..7c3e68d9ada5 100644
@@ -10,6 +10,7 @@ obj-$(CONFIG_SAMPLE_RUST_DRIVER_PLATFORM)	+= rust_driver_platform.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_FAUX)		+= rust_driver_faux.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_AUXILIARY)	+= rust_driver_auxiliary.o
 obj-$(CONFIG_SAMPLE_RUST_CONFIGFS)		+= rust_configfs.o
+obj-$(CONFIG_SAMPLE_RUST_ALLOC)		+= rust_alloc.o

I think adding an example for large alignment is fine, but let's do this in a doc-test on VBox in rust/kernel/alloc/kbox.rs. I think adding a separate module for this is overkill.

Note that doc-tests are executed on boot if CONFIG_RUST_KERNEL_DOCTESTS=y.

Quoted 15 lines
samples/rust/rust_alloc.rs new file +9 -0
new file mode 100644
index 000000000000..61efde37b5f2
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0
+
+// Copyright (c) 2025, Kylin Software
+
+//! Rust alloc sample.
+
+use kernel::bindings;
+use kernel::prelude::*;
+

samples/rust/rust_alloc.rs line 19

Quoted 10 lines
samples/rust/rust_alloc.rs new file +10 -0
+module! {
+    type: RustAlloc,
+    name: "rust_alloc",
+    authors: ["Rust for Linux Contributors"],
+    description: "Rust alloc sample",
+    license: "GPL",
+}
+
+const VBOX_SIZE: usize = 1024;
+const VBOX_LARGE_ALIGN: usize = bindings::PAGE_SIZE * 4;

Please use kernel::page::PAGE_SIZE instead.

Quoted 17 lines
samples/rust/rust_alloc.rs new file +17 -0
+const KVEC_VAL: [usize; 3] = [10, 20, 30];
+
+#[repr(align(128))]
+struct VboxBlob([u8; VBOX_SIZE]);
+
+// This structure is used to test the allocation of alignments larger
+// than PAGE_SIZE.
+// Since this is not yet supported, avoid accessing the contents of
+// the structure for now.
+#[allow(dead_code)]
+#[repr(align(8192))]
+struct VboxLargeAlignBlob([u8; VBOX_LARGE_ALIGN]);
+
+struct RustAlloc {
+    vbox_blob: VBox<VboxBlob>,
+    kvec_blob: KVec<usize>,
+}

samples/rust/rust_alloc.rs line 46

Quoted 10 lines
samples/rust/rust_alloc.rs new file +10 -0
+
+fn check_align(addr: usize, align: usize) -> bool {
+    debug_assert!(align.is_power_of_two());
+    if addr & (align - 1) != 0 {
+        pr_err!("Address {:#x} is not aligned with {:#x}.\n", addr, align);
+        false
+    } else {
+        true
+    }
+}

I think check_align() is unnecessary -- we don't need to test this in this context.

Instead, I suggest to add some doc-tests to the Allocator impls for Kmalloc, Vmalloc and KVmalloc in rust/kernel/alloc/allocator.rs testing that they return the expected alignment. This would be a valuable test case for those. If you're interested in adding them, please feel free to do so. :)

samples/rust/rust_alloc.rs line 56

Quoted 9 lines
samples/rust/rust_alloc.rs new file +9 -0
+impl kernel::Module for RustAlloc {
+    fn init(_module: &'static ThisModule) -> Result<Self> {
+        pr_info!("Rust allocator sample (init)\n");
+
+        let vbox_blob = VBox::<VboxBlob>::new_uninit(GFP_KERNEL)?;
+        if !check_align(vbox_blob.as_ptr() as usize, 128) {
+            return Err(EINVAL);
+        }
+        let vbox_blob = vbox_blob.write(VboxBlob([0xfeu8; VBOX_SIZE]));

Given that you initialize it with a value anyways, you can just do

	let blob = VBox::new(Blob([0xfeu8; SIZE]), GFP_KERNEL)?;

instead.

samples/rust/rust_alloc.rs line 61

Quoted 4 lines
samples/rust/rust_alloc.rs new file +4 -0
+        if let Ok(_) = VBox::<VboxLargeAlignBlob>::new_uninit(GFP_KERNEL) {
+            pr_err!("Allocations for VBox with alignments larger than PAGE_SIZE should fail, but here it succeeded.\n");
+            return Err(EINVAL);
+        }

This can just be

	assert!(VBox::<VboxLargeAlignBlob>::new_uninit(GFP_KERNEL).is_err());

within a doc-test.

samples/rust/rust_alloc.rs line 64

Quoted 2 lines
samples/rust/rust_alloc.rs new file +2 -0
+        let mut kvec_blob = KVec::new();
+        kvec_blob.extend_from_slice(&KVEC_VAL, GFP_KERNEL)?;

We already have doc-tests for KVec::new() and KVec::extend_from_slice() in rust/kernel/alloc/kvec.rs.

Quoted 11 lines
samples/rust/rust_alloc.rs new file +11 -0
+        Ok(Self {
+            vbox_blob,
+            kvec_blob,
+        })
+    }
+}
+
+impl Drop for RustAlloc {
+    fn drop(&mut self) {
+        pr_info!("Rust allocator sample (exit)\n");
+

samples/rust/rust_alloc.rs line 86

Quoted 10 lines
samples/rust/rust_alloc.rs new file +10 -0
+        // check the values
+        for b in self.vbox_blob.0.as_slice().iter() {
+            if *b != 0xfeu8 {
+                pr_err!("vbox_blob contains wrong values\n");
+            }
+        }
+
+        if self.kvec_blob.as_slice() != KVEC_VAL {
+            pr_err!("kvec_blob contains wrong values\n");
+        }

Here you're basically testing Vec::as_slice(). We don't have doc-tests for as_slice() and as_slice_mut() in rust/kernel/alloc/kvec.rs. Please feel free to add them. :)

Quoted 2 lines
samples/rust/rust_alloc.rs new file +2 -0
+    }
+}
#2 lore raw
Quoted 15 lines · Danilo Krummrich

(Cc: Lorenzo, Vlastimil, Liam, Uladzislau)

samples/rust/Makefile obj-$(CONFIG_SAMPLE_RUST_DRIVER_PLATFORM) += rust_driver_platform.o · line 13

Quoted 9 lines · Hui Zhu
samples/rust/Makefile +1 -0
index bd2faad63b4f..7c3e68d9ada5 100644
@@ -10,6 +10,7 @@ obj-$(CONFIG_SAMPLE_RUST_DRIVER_PLATFORM)	+= rust_driver_platform.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_FAUX)		+= rust_driver_faux.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_AUXILIARY)	+= rust_driver_auxiliary.o
 obj-$(CONFIG_SAMPLE_RUST_CONFIGFS)		+= rust_configfs.o
+obj-$(CONFIG_SAMPLE_RUST_ALLOC)		+= rust_alloc.o

I think adding an example for large alignment is fine, but let's do this in a doc-test on VBox in rust/kernel/alloc/kbox.rs. I think adding a separate module

I would suggest using #[kunit_tests(..)], which is similar to how doc-test run, for it if we only use it for test purposes.

Regards,
Boqun

Quoted 4 lines

for this is overkill.

Note that doc-tests are executed on boot if CONFIG_RUST_KERNEL_DOCTESTS=y.

[...]

author
#3 lore raw

Hi Danilo and Boqun,

Quoted 20 lines · Boqun Feng
Quoted 15 lines · Danilo Krummrich

(Cc: Lorenzo, Vlastimil, Liam, Uladzislau)

samples/rust/Makefile obj-$(CONFIG_SAMPLE_RUST_DRIVER_PLATFORM) += rust_driver_platform.o · line 13

Quoted 9 lines · Hui Zhu
samples/rust/Makefile +1 -0
index bd2faad63b4f..7c3e68d9ada5 100644
@@ -10,6 +10,7 @@ obj-$(CONFIG_SAMPLE_RUST_DRIVER_PLATFORM)	+= rust_driver_platform.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_FAUX)		+= rust_driver_faux.o
 obj-$(CONFIG_SAMPLE_RUST_DRIVER_AUXILIARY)	+= rust_driver_auxiliary.o
 obj-$(CONFIG_SAMPLE_RUST_CONFIGFS)		+= rust_configfs.o
+obj-$(CONFIG_SAMPLE_RUST_ALLOC)		+= rust_alloc.o

I think adding an example for large alignment is fine, but let's do this in a doc-test on VBox in rust/kernel/alloc/kbox.rs. I think adding a separate module

I would suggest using #[kunit_tests(..)], which is similar to how doc-test run, for it if we only use it for test purposes.

Quoted 8 lines

Regards,
Boqun

Quoted 4 lines

for this is overkill.

Note that doc-tests are executed on boot if CONFIG_RUST_KERNEL_DOCTESTS=y.

[...]

I sent version v3 that move vbox code to allocator as unit tests and add move kvec::as_slice to doc example.

Best,
Hui