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rust/vmstate: Add support for field_exists checks

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Unfortunately, at present it's not possible to have a const
"with_exist_check" method to append test_fn after vmstate_struct (due
to error on "constant functions cannot evaluate destructors" for `F`).

Before the vmstate builder, the only way to support "test_fn" is to
extend vmstate_struct macro to add the such new optional member (and
fortunately, Rust can still parse the current expansion!).

Abstract the previous callback implementation of vmstate_validate into
a separate macro, and moves it before vmstate_struct for vmstate_struct
to call.

Note that there's no need to add any extra flag for a new test_fn added
in the VMStateField.

Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20250414144943.1112885-2-zhao1.liu@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Zhao Liu 2025-04-14 22:49:35 +08:00 • committed by Paolo Bonzini
parent 5134cf9b5d
commit 6f8e6aed81
1 changed files with 37 additions and 33 deletions
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70
rust/qemu-api/src/vmstate.rs
View file

@ -200,13 +200,14 @@ pub const fn vmstate_varray_flag<T: VMState>(_: PhantomData<T>) -> VMStateFlags
/// and [`impl_vmstate_forward!`](crate::impl_vmstate_forward) help with this.
#[macro_export]
macro_rules! vmstate_of {
($struct_name:ty, $field_name:ident $([0 .. $num:ident $(* $factor:expr)?])? $(,)?) => {
($struct_name:ty, $field_name:ident $([0 .. $num:ident $(* $factor:expr)?])? $(, $test_fn:expr)? $(,)?) => {
$crate::bindings::VMStateField {
name: ::core::concat!(::core::stringify!($field_name), "\0")
.as_bytes()
.as_ptr() as *const ::std::os::raw::c_char,
offset: $crate::offset_of!($struct_name, $field_name),
$(num_offset: $crate::offset_of!($struct_name, $num),)?
$(field_exists: $crate::vmstate_exist_fn!($struct_name, $test_fn),)?
// The calls to `call_func_with_field!` are the magic that
// computes most of the VMStateField from the type of the field.
info: $crate::info_enum_to_ref!($crate::call_func_with_field!(
@ -435,6 +436,38 @@ macro_rules! vmstate_unused {
}};
}
pub extern "C" fn rust_vms_test_field_exists<T, F: for<'a> FnCall<(&'a T, u8), bool>>(
opaque: *mut c_void,
version_id: c_int,
) -> bool {
// SAFETY: the opaque was passed as a reference to `T`.
let owner: &T = unsafe { &*(opaque.cast::<T>()) };
let version: u8 = version_id.try_into().unwrap();
F::call((owner, version))
}
pub type VMSFieldExistCb = unsafe extern "C" fn(
opaque: *mut std::os::raw::c_void,
version_id: std::os::raw::c_int,
) -> bool;
#[macro_export]
macro_rules! vmstate_exist_fn {
($struct_name:ty, $test_fn:expr) => {{
const fn test_cb_builder__<T, F: for<'a> $crate::callbacks::FnCall<(&'a T, u8), bool>>(
_phantom: ::core::marker::PhantomData<F>,
) -> $crate::vmstate::VMSFieldExistCb {
let _: () = F::ASSERT_IS_SOME;
$crate::vmstate::rust_vms_test_field_exists::<T, F>
}
const fn phantom__<T>(_: &T) -> ::core::marker::PhantomData<T> {
::core::marker::PhantomData
}
Some(test_cb_builder__::<$struct_name, _>(phantom__(&$test_fn)))
}};
}
// FIXME: including the `vmsd` field in a `const` is not possible without
// the const_refs_static feature (stabilized in Rust 1.83.0). Without it,
// it is not possible to use VMS_STRUCT in a transparent manner using
@ -445,7 +478,7 @@ macro_rules! vmstate_unused {
#[doc(alias = "VMSTATE_STRUCT")]
#[macro_export]
macro_rules! vmstate_struct {
($struct_name:ty, $field_name:ident $([0 .. $num:ident $(* $factor:expr)?])?, $vmsd:expr, $type:ty $(,)?) => {
($struct_name:ty, $field_name:ident $([0 .. $num:ident $(* $factor:expr)?])?, $vmsd:expr, $type:ty $(, $test_fn:expr)? $(,)?) => {
$crate::bindings::VMStateField {
name: ::core::concat!(::core::stringify!($field_name), "\0")
.as_bytes()
@ -458,6 +491,7 @@ macro_rules! vmstate_struct {
size: ::core::mem::size_of::<$type>(),
flags: $crate::bindings::VMStateFlags::VMS_STRUCT,
vmsd: $vmsd,
$(field_exists: $crate::vmstate_exist_fn!($struct_name, $test_fn),)?
..$crate::zeroable::Zeroable::ZERO
} $(.with_varray_flag_unchecked(
$crate::call_func_with_field!(
@ -514,43 +548,13 @@ macro_rules! vmstate_fields {
}}
}
pub extern "C" fn rust_vms_test_field_exists<T, F: for<'a> FnCall<(&'a T, u8), bool>>(
opaque: *mut c_void,
version_id: c_int,
) -> bool {
let owner: &T = unsafe { &*(opaque.cast::<T>()) };
let version: u8 = version_id.try_into().unwrap();
// SAFETY: the opaque was passed as a reference to `T`.
F::call((owner, version))
}
pub type VMSFieldExistCb = unsafe extern "C" fn(
opaque: *mut std::os::raw::c_void,
version_id: std::os::raw::c_int,
) -> bool;
#[doc(alias = "VMSTATE_VALIDATE")]
#[macro_export]
macro_rules! vmstate_validate {
($struct_name:ty, $test_name:expr, $test_fn:expr $(,)?) => {
$crate::bindings::VMStateField {
name: ::std::ffi::CStr::as_ptr($test_name),
field_exists: {
const fn test_cb_builder__<
T,
F: for<'a> $crate::callbacks::FnCall<(&'a T, u8), bool>,
>(
_phantom: ::core::marker::PhantomData<F>,
) -> $crate::vmstate::VMSFieldExistCb {
let _: () = F::ASSERT_IS_SOME;
$crate::vmstate::rust_vms_test_field_exists::<T, F>
}
const fn phantom__<T>(_: &T) -> ::core::marker::PhantomData<T> {
::core::marker::PhantomData
}
Some(test_cb_builder__::<$struct_name, _>(phantom__(&$test_fn)))
},
field_exists: $crate::vmstate_exist_fn!($struct_name, $test_fn),
flags: $crate::bindings::VMStateFlags(
$crate::bindings::VMStateFlags::VMS_MUST_EXIST.0
| $crate::bindings::VMStateFlags::VMS_ARRAY.0,