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// Copyright (c) Microsoft Corporation.
// Licensed under the MIT License.
//! Traits and types for save/restore support.
//!
//! To implement save/restore for your device or state unit, you must do these
//! things:
//!
//! 1. You define a saved state type. This type needs to be stable across
//! releases, so you should not share types with your implementation even if
//! they are currently identical. By decoupling your runtime types and your
//! saved state types, you are much less likely to accidentally break saved
//! state compatibility.
//!
//! 2. `derive` some traits on your type. Specifically, you must derive
//! [`Protobuf`] so that your type can be encoded into protobuf format, and
//! any fields in your type must also implement [`Protobuf`].
//!
//! So that your saved state type can show up in generated `.proto` files,
//! you must also set an attribute `#[mesh(package = "my.package.name")]`.
//! This specifies the protobuf package, as well as the file name of your
//! protobuf file. For the root object of your device's saved state, this
//! package name becomes part of the serialized state, so you cannot change
//! it later.
//!
//! Finally, in the root object of your saved state, you must additionally
//! derive [`SavedStateRoot`]. This provides some additional metadata so that
//! we can find your saved state type and generate a `.proto` file from it
//! for analysis. You only need to put this on the root types or types that
//! will be converted to [`SavedStateBlob`]; the infrastructure will find any
//! dependent types. But it doesn't hurt to put it on other types, too.
//!
//! 3. Typically, you implement the [`SaveRestore`] trait. This trait allows you
//! to specify your associated saved state type and to implement `save` and
//! `restore` methods that act on this type.
//!
//! For some device types (such as vmbus devices), you may need to use a
//! device-specific trait that provides additional parameters. But the
//! pattern should be the same.
#![warn(missing_docs)]
/// Derives [`SavedStateRoot`] for a type.
///
/// This ensures that a saved state blob's metadata can be found, so that it can
/// be used to generate .proto files and perform offline analysis of saved state
/// compatibility.
///
/// To use this, you must also derive [`Protobuf`] and set a protobuf package
/// for your type. The package name should be defined to group related types
/// together; typically the same package should be used for all types defined in
/// a module.
///
/// For example:
///
/// ```rust
/// # use vmcore::save_restore::{SavedStateRoot, SavedStateBlob};
/// # use mesh::payload::Protobuf;
/// #[derive(Protobuf, SavedStateRoot)]
/// #[mesh(package = "test.my_device")]
/// struct MySavedState {
/// #[mesh(1)]
/// active: bool,
/// }
///
/// // This will now compile.
/// let _blob = SavedStateBlob::new(MySavedState { active: true });
/// ```
pub use save_restore_derive::SavedStateRoot;
use mesh::payload;
use mesh::payload::encoding::ImpossibleField;
use mesh::payload::message::ProtobufAny;
use mesh::payload::protofile::MessageDescription;
use mesh::payload::DefaultEncoding;
use mesh::payload::DescribedProtobuf;
use mesh::payload::Protobuf;
/// Implemented by objects which can be saved/restored
pub trait SaveRestore {
/// The concrete saved state type.
type SavedState;
/// Saves the object's state.
fn save(&mut self) -> Result<Self::SavedState, SaveError>;
/// Restores the object's state.
fn restore(&mut self, state: Self::SavedState) -> Result<(), RestoreError>;
}
/// Convenience type for objects that do not support being saved.
pub enum SavedStateNotSupported {}
impl DefaultEncoding for SavedStateNotSupported {
type Encoding = ImpossibleField;
}
impl SavedStateRoot for SavedStateNotSupported {
// This type should not be included in the .proto output.
fn do_not_impl_this_manually(&self) {}
}
/// Convenience type for objects that have no saved state.
#[derive(Protobuf, SavedStateRoot)]
#[mesh(package = "save_restore")]
pub struct NoSavedState;
/// Trait implemented by objects that implement `SaveRestore` with an associated
/// type that can be serialized as a protobuf message.
pub trait ProtobufSaveRestore {
/// Save the object.
fn save(&mut self) -> Result<SavedStateBlob, SaveError>;
/// Restore the object.
fn restore(&mut self, state: SavedStateBlob) -> Result<(), RestoreError>;
}
/// An opaque saved state blob, encoded as a protobuf message.
#[derive(Debug, Protobuf)]
#[mesh(transparent)]
pub struct SavedStateBlob(ProtobufAny);
/// Trait implemented by "root" saved state blobs, which are ones that either
/// form the root of a saved state tree, or at points in the tree where the type
/// is not known at compile time.
///
/// **Do not implement this trait manually.** Derive it with
/// `#[derive(SavedStateRoot)]`. This emits extra code to ensure that the saved
/// state type metadata is included in the binary.
pub trait SavedStateRoot: DescribedProtobuf {
#[doc(hidden)]
fn do_not_impl_this_manually(&self);
}
impl SavedStateBlob {
/// Encodes `data` as a protobuf message.
pub fn new<T: SavedStateRoot>(data: T) -> Self {
Self(ProtobufAny::new(data))
}
/// Decodes the protobuf message into `T`.
pub fn parse<T: SavedStateRoot>(&self) -> Result<T, payload::Error> {
self.0.parse()
}
}
impl<T: SaveRestore> ProtobufSaveRestore for T
where
T::SavedState: 'static + Send + SavedStateRoot,
{
fn save(&mut self) -> Result<SavedStateBlob, SaveError> {
self.save().map(SavedStateBlob::new)
}
fn restore(&mut self, state: SavedStateBlob) -> Result<(), RestoreError> {
self.restore(state.parse()?)
}
}
/// A restore error.
#[derive(Debug, thiserror::Error)]
pub enum RestoreError {
/// unknown entry ID
#[error("unknown entry id: {0}")]
UnknownEntryId(String),
/// restore failure in a child object
#[error("failed to restore child device {0}")]
ChildError(String, #[source] Box<RestoreError>),
/// failure to decode a protobuf object
#[error("failed to decode protobuf")]
ProtobufDecode(#[from] payload::Error),
/// this object does not support save state
#[error("unexpected saved state")]
SavedStateNotSupported,
/// custom saved state corruption error
#[error("saved state is invalid")]
InvalidSavedState(#[source] anyhow::Error),
/// non-state-related restore failure
#[error(transparent)]
Other(anyhow::Error),
}
/// A save error.
#[derive(Debug, thiserror::Error)]
pub enum SaveError {
/// This object does not support saved state.
#[error("save state not supported")]
NotSupported,
/// Save failed in child object.
#[error("failed to save child device {0}")]
ChildError(String, #[source] Box<SaveError>),
/// Save failed due to some other error.
#[error(transparent)]
Other(anyhow::Error),
/// The child saved state is invalid.
#[error("child saved state is invalid")]
InvalidChildSavedState(#[source] anyhow::Error),
}
/// A save operation error.
#[derive(Debug, thiserror::Error)]
pub enum CollectError {
/// some save results are missing
#[error("failed to receive all save results")]
MissingResults,
/// got more save results than expected
#[error("received more results than expected")]
TooManyResults,
/// a save payload is corrupted
#[error("received bad payload")]
BadPayload(#[source] payload::Error),
}
/// Gets the message descriptions for all types deriving [`SavedStateRoot`].
///
/// This can be used with
/// [`DescriptorWriter`](mesh::payload::protofile::DescriptorWriter) to write
/// `.proto` files for the saved states.
pub fn saved_state_roots() -> impl Iterator<Item = &'static MessageDescription<'static>> {
private::SAVED_STATE_ROOTS.iter().flatten().copied()
}
// For `save_restore_derive`
#[doc(hidden)]
pub mod private {
pub use linkme;
pub use mesh::payload::protofile;
// Use Option<&X> in case the linker inserts some stray nulls, as we think
// it might on Windows.
//
// See <https://devblogs.microsoft.com/oldnewthing/20181108-00/?p=100165>.
#[linkme::distributed_slice]
pub static SAVED_STATE_ROOTS: [Option<&'static protofile::MessageDescription<'static>>] = [..];
// Always have at least one entry to work around linker bugs.
//
// See <https://github.com/llvm/llvm-project/issues/65855>.
#[linkme::distributed_slice(SAVED_STATE_ROOTS)]
static WORKAROUND: Option<&'static protofile::MessageDescription<'static>> = None;
#[doc(hidden)]
#[macro_export]
macro_rules! declare_saved_state_root {
($ident:ty) => {
impl $crate::save_restore::SavedStateRoot for $ident {
fn do_not_impl_this_manually(&self) {}
}
const _: () = {
use $crate::save_restore::private::{linkme, protofile, SAVED_STATE_ROOTS};
#[linkme::distributed_slice(SAVED_STATE_ROOTS)]
#[linkme(crate = linkme)]
static DESCRIPTION: Option<&'static protofile::MessageDescription<'static>> =
Some(&protofile::message_description::<$ident>());
};
};
}
}