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

[Paolo Bonzini <pbonzini@redhat.com>]

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