[PATCH 2/2] rust: block/mq: replace mem::zeroed() with Zeroable trait

Paolo Bonzini
2024-11-28T14:13:33Z

Isolate the unsafety in the declaration of the Zeroable trait, instead of having
to use "unsafe" just to declare a struct. This is more similar to how you would
use "..Default::default()" (which is also a possibility here, but arguably
less efficient).

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
rust/kernel/block/mq/gen_disk.rs | 8 +++++---
rust/kernel/block/mq/tag_set.rs | 10 ++++++----
2 files changed, 11 insertions(+), 7 deletions(-)

diff --git a/rust/kernel/block/mq/gen_disk.rs b/rust/kernel/block/mq/gen_disk.rs
index 708125dce96a..65342d065296 100644
--- a/rust/kernel/block/mq/gen_disk.rs
+++ b/rust/kernel/block/mq/gen_disk.rs
@@ -6,7 +6,7 @@
//! C header: [`include/linux/blk_mq.h`](srctree/include/linux/blk_mq.h)

use crate::block::mq::{raw_writer::RawWriter, Operations, TagSet};
-use crate::{bindings, error::from_err_ptr, error::Result, sync::Arc};
+use crate::{bindings, error::from_err_ptr, error::Result, init::Zeroable, sync::Arc};
use crate::{error, static_lock_class};
use core::fmt::{self, Write};

@@ -31,6 +31,9 @@ fn default() -> Self {
}
}

+// SAFETY: `bindings::queue_limits` contains only fields that are valid when zeroed.
+unsafe impl Zeroable for bindings::queue_limits {}
+
impl GenDiskBuilder {
/// Create a new instance.
pub fn new() -> Self {
@@ -93,8 +96,7 @@ pub fn build<T: Operations>(
name: fmt::Arguments<'_>,
tagset: Arc<TagSet<T>>,
) -> Result<GenDisk<T>> {
- // SAFETY: `bindings::queue_limits` contain only fields that are valid when zeroed.
- let mut lim: bindings::queue_limits = unsafe { core::mem::zeroed() };
+ let mut lim: bindings::queue_limits = Zeroable::ZERO;

lim.logical_block_size = self.logical_block_size;
lim.physical_block_size = self.physical_block_size;
diff --git a/rust/kernel/block/mq/tag_set.rs b/rust/kernel/block/mq/tag_set.rs
index f9a1ca655a35..1ff7366ca549 100644
--- a/rust/kernel/block/mq/tag_set.rs
+++ b/rust/kernel/block/mq/tag_set.rs
@@ -10,6 +10,7 @@
bindings,
block::mq::{operations::OperationsVTable, request::RequestDataWrapper, Operations},
error,
+ init::Zeroable,
prelude::PinInit,
try_pin_init,
types::Opaque,
@@ -32,6 +33,10 @@ pub struct TagSet<T: Operations> {
_p: PhantomData<T>,
}

+// SAFETY: `blk_mq_tag_set` only contains integers and pointers, which
+// all are allowed to be 0.
+unsafe impl Zeroable for bindings::blk_mq_tag_set {}
+
impl<T: Operations> TagSet<T> {
/// Try to create a new tag set
pub fn new(
@@ -39,9 +44,6 @@ pub fn new(
num_tags: u32,
num_maps: u32,
) -> impl PinInit<Self, error::Error> {
- // SAFETY: `blk_mq_tag_set` only contains integers and pointers, which
- // all are allowed to be 0.
- let tag_set: bindings::blk_mq_tag_set = unsafe { core::mem::zeroed() };
let tag_set = core::mem::size_of::<RequestDataWrapper>()
.try_into()
.map(|cmd_size| {
@@ -55,7 +57,7 @@ pub fn new(
flags: bindings::BLK_MQ_F_SHOULD_MERGE,
driver_data: core::ptr::null_mut::<core::ffi::c_void>(),
nr_maps: num_maps,
- ..tag_set
+ ..Zeroable::ZERO
}
});

--
2.47.0