MaybeUninit::zeroed() is handy, but it introduces unsafe (and has a pretty heavy
syntax in general) and anyway it is not available as a "const" function until
Rust 1.75.0.
Introduce a trait that provides the same functionality while staying within
safe Rust. In the future we may want to add automatic derivation and
implementation of the trait, once we can assume Rust 1.75.0; for now the
implementation is manual.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
rust/hw/char/pl011/src/device_class.rs | 5 +-
rust/hw/char/pl011/src/memory_ops.rs | 11 ++--
rust/qemu-api/meson.build | 1 +
rust/qemu-api/src/device_class.rs | 4 +-
rust/qemu-api/src/lib.rs | 1 +
rust/qemu-api/src/zeroable.rs | 75 ++++++++++++++++++++++++++
6 files changed, 89 insertions(+), 8 deletions(-)
create mode 100644 rust/qemu-api/src/zeroable.rs
diff --git a/rust/hw/char/pl011/src/device_class.rs b/rust/hw/char/pl011/src/device_class.rs
index a3d1b1e929a..37bbf6d36cc 100644
--- a/rust/hw/char/pl011/src/device_class.rs
+++ b/rust/hw/char/pl011/src/device_class.rs
@@ -7,7 +7,8 @@
use qemu_api::{
bindings::*,
c_str,
- definitions::ObjectImpl
+ definitions::ObjectImpl,
+ zeroable::Zeroable,
};
use crate::device::PL011State;
@@ -16,7 +17,7 @@
pub static VMSTATE_PL011: VMStateDescription = VMStateDescription {
name: PL011State::TYPE_INFO.name,
unmigratable: true,
- ..unsafe { ::core::mem::MaybeUninit::<VMStateDescription>::zeroed().assume_init() }
+ ..Zeroable::ZERO
};
qemu_api::declare_properties! {
diff --git a/rust/hw/char/pl011/src/memory_ops.rs b/rust/hw/char/pl011/src/memory_ops.rs
index 2c664fd45ed..88d17ec2e3a 100644
--- a/rust/hw/char/pl011/src/memory_ops.rs
+++ b/rust/hw/char/pl011/src/memory_ops.rs
@@ -2,11 +2,14 @@
// Author(s): Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
// SPDX-License-Identifier: GPL-2.0-or-later
-use core::{mem::MaybeUninit, ptr::NonNull};
+use core::ptr::NonNull;
use std::os::raw::{c_uint, c_void};
-use qemu_api::bindings::*;
+use qemu_api::{
+ bindings::*,
+ zeroable::Zeroable
+};
use crate::device::PL011State;
@@ -16,11 +19,11 @@
read_with_attrs: None,
write_with_attrs: None,
endianness: device_endian::DEVICE_NATIVE_ENDIAN,
- valid: unsafe { MaybeUninit::<MemoryRegionOps__bindgen_ty_1>::zeroed().assume_init() },
+ valid: Zeroable::ZERO,
impl_: MemoryRegionOps__bindgen_ty_2 {
min_access_size: 4,
max_access_size: 4,
- ..unsafe { MaybeUninit::<MemoryRegionOps__bindgen_ty_2>::zeroed().assume_init() }
+ ..Zeroable::ZERO
},
};
diff --git a/rust/qemu-api/meson.build b/rust/qemu-api/meson.build
index 57f813fc8f9..547fc5caa3a 100644
--- a/rust/qemu-api/meson.build
+++ b/rust/qemu-api/meson.build
@@ -14,6 +14,7 @@ _qemu_api_rs = static_library(
'src/device_class.rs',
'src/offset_of.rs',
'src/tests.rs',
+ 'src/zeroable.rs',
],
{'.' : bindings_rs},
),
diff --git a/rust/qemu-api/src/device_class.rs b/rust/qemu-api/src/device_class.rs
index d4fa544df39..d2535125c48 100644
--- a/rust/qemu-api/src/device_class.rs
+++ b/rust/qemu-api/src/device_class.rs
@@ -100,7 +100,7 @@ const fn _calc_prop_len() -> usize {
fn _make_properties() -> [$crate::bindings::Property; PROP_LEN] {
[
$($prop),*,
- unsafe { ::core::mem::MaybeUninit::<$crate::bindings::Property>::zeroed().assume_init() },
+ $crate::zeroable::Zeroable::ZERO,
]
}
@@ -125,7 +125,7 @@ macro_rules! vm_state_description {
$vname.as_ptr()
},)*
unmigratable: true,
- ..unsafe { ::core::mem::MaybeUninit::<$crate::bindings::VMStateDescription>::zeroed().assume_init() }
+ ..$crate::zeroable::Zeroable::ZERO
};
}
}
diff --git a/rust/qemu-api/src/lib.rs b/rust/qemu-api/src/lib.rs
index 082f1addb10..50951d20e14 100644
--- a/rust/qemu-api/src/lib.rs
+++ b/rust/qemu-api/src/lib.rs
@@ -31,6 +31,7 @@ unsafe impl Sync for bindings::VMStateDescription {}
pub mod definitions;
pub mod device_class;
pub mod offset_of;
+pub mod zeroable;
#[cfg(test)]
mod tests;
diff --git a/rust/qemu-api/src/zeroable.rs b/rust/qemu-api/src/zeroable.rs
new file mode 100644
index 00000000000..faa93d1fb33
--- /dev/null
+++ b/rust/qemu-api/src/zeroable.rs
@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+use std::ptr;
+
+/// This trait provides a replacement for core::mem::zeroed() that can be
+/// used as a `const fn` prior to Rust 1.75.0. As an added bonus it removes
+/// usage of `unsafe` blocks.
+///
+/// Unlike other Zeroable traits found in other crates (e.g.
+/// [`pinned_init`](https://docs.rs/pinned-init/latest/pinned_init/trait.Zeroable.html))
+/// this is a safe trait because the value `ZERO` constant has to be written by
+/// hand. The `pinned_init` crate instead makes the trait unsafe, but it
+/// provides a `#[derive(Zeroable)]` macro to define it with compile-time
+/// safety checks. Once we can assume Rust 1.75.0 is available, we could
+/// switch to their idea, and use `core::mem::zeroed()` to provide a blanked
+/// implementation of the `ZERO` constant.
+pub trait Zeroable: Default {
+ const ZERO: Self;
+}
+
+impl Zeroable for crate::bindings::Property__bindgen_ty_1 {
+ const ZERO: Self = Self { i: 0 };
+}
+
+impl Zeroable for crate::bindings::Property {
+ const ZERO: Self = Self {
+ name: ptr::null(),
+ info: ptr::null(),
+ offset: 0,
+ bitnr: 0,
+ bitmask: 0,
+ set_default: false,
+ defval: Zeroable::ZERO,
+ arrayoffset: 0,
+ arrayinfo: ptr::null(),
+ arrayfieldsize: 0,
+ link_type: ptr::null(),
+ };
+}
+
+impl Zeroable for crate::bindings::VMStateDescription {
+ const ZERO: Self = Self {
+ name: ptr::null(),
+ unmigratable: false,
+ early_setup: false,
+ version_id: 0,
+ minimum_version_id: 0,
+ priority: crate::bindings::MigrationPriority::MIG_PRI_DEFAULT,
+ pre_load: None,
+ post_load: None,
+ pre_save: None,
+ post_save: None,
+ needed: None,
+ dev_unplug_pending: None,
+ fields: ptr::null(),
+ subsections: ptr::null(),
+ };
+}
+
+impl Zeroable for crate::bindings::MemoryRegionOps__bindgen_ty_1 {
+ const ZERO: Self = Self {
+ min_access_size: 0,
+ max_access_size: 0,
+ unaligned: false,
+ accepts: None,
+ };
+}
+
+impl Zeroable for crate::bindings::MemoryRegionOps__bindgen_ty_2 {
+ const ZERO: Self = Self {
+ min_access_size: 0,
+ max_access_size: 0,
+ unaligned: false,
+ };
+}
--
2.46.2