Provide an implementation of std::error::Error that bridges the Rust anyhow::Error and std::panic::Location types with QEMU's Error*. It also has several utility methods, analogous to error_propagate(), that convert a Result into a return value + Error** pair.
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com> --- rust/Cargo.lock | 17 +++ rust/Cargo.toml | 1 + rust/qemu-api/Cargo.toml | 2 + rust/qemu-api/meson.build | 1 + rust/qemu-api/src/error.rs | 299 +++++++++++++++++++++++++++++++++++++ rust/qemu-api/src/lib.rs | 3 + 6 files changed, 323 insertions(+) create mode 100644 rust/qemu-api/src/error.rs diff --git a/rust/Cargo.lock b/rust/Cargo.lock index 13d580c693b..961005bb513 100644 --- a/rust/Cargo.lock +++ b/rust/Cargo.lock @@ -2,6 +2,12 @@ # It is not intended for manual editing. version = 3 +[[package]] +name = "anyhow" +version = "1.0.98" +source = "registry+https://github.com/rust-lang/crates.io-index"; +checksum = "e16d2d3311acee920a9eb8d33b8cbc1787ce4a264e85f964c2404b969bdcd487" + [[package]] name = "arbitrary-int" version = "1.2.7" @@ -37,6 +43,15 @@ version = "1.12.0" source = "registry+https://github.com/rust-lang/crates.io-index"; checksum = "3dca9240753cf90908d7e4aac30f630662b02aebaa1b58a3cadabdb23385b58b" +[[package]] +name = "foreign" +version = "0.3.1" +source = "registry+https://github.com/rust-lang/crates.io-index"; +checksum = "17ca1b5be8c9d320daf386f1809c7acc0cb09accbae795c2001953fa50585846" +dependencies = [ + "libc", +] + [[package]] name = "hpet" version = "0.1.0" @@ -106,6 +121,8 @@ dependencies = [ name = "qemu_api" version = "0.1.0" dependencies = [ + "anyhow", + "foreign", "libc", "qemu_api_macros", ] diff --git a/rust/Cargo.toml b/rust/Cargo.toml index a00b8ad0bcd..26f3ec09d3d 100644 --- a/rust/Cargo.toml +++ b/rust/Cargo.toml @@ -66,6 +66,7 @@ missing_safety_doc = "deny" mut_mut = "deny" needless_bitwise_bool = "deny" needless_pass_by_ref_mut = "deny" +needless_update = "deny" no_effect_underscore_binding = "deny" option_option = "deny" or_fun_call = "deny" diff --git a/rust/qemu-api/Cargo.toml b/rust/qemu-api/Cargo.toml index c96cf50e7a1..db7000dee44 100644 --- a/rust/qemu-api/Cargo.toml +++ b/rust/qemu-api/Cargo.toml @@ -15,7 +15,9 @@ rust-version.workspace = true [dependencies] qemu_api_macros = { path = "../qemu-api-macros" } +anyhow = "~1.0" libc = "0.2.162" +foreign = "~0.3.1" [features] default = ["debug_cell"] diff --git a/rust/qemu-api/meson.build b/rust/qemu-api/meson.build index aa22252866d..ef0de51266b 100644 --- a/rust/qemu-api/meson.build +++ b/rust/qemu-api/meson.build @@ -19,6 +19,7 @@ _qemu_api_rs = static_library( 'src/cell.rs', 'src/chardev.rs', 'src/errno.rs', + 'src/error.rs', 'src/irq.rs', 'src/memory.rs', 'src/module.rs', diff --git a/rust/qemu-api/src/error.rs b/rust/qemu-api/src/error.rs new file mode 100644 index 00000000000..0bdd413a0a2 --- /dev/null +++ b/rust/qemu-api/src/error.rs @@ -0,0 +1,299 @@ +// SPDX-License-Identifier: GPL-2.0-or-later + +//! Error propagation for QEMU Rust code +//! +//! In QEMU, an `Error` usually consists of a message and an errno value. +//! In this wrapper, the errno value is replaced by an [`anyhow::Error`] +//! so that it is easy to pass any other Rust error type up to C code. +//! Note that the backtrace that is provided by `anyhow` is not used yet, +//! only the message ends up in the QEMU `Error*`. +//! +//! The message part can be used to clarify the inner error, similar to +//! `error_prepend`, and of course to describe an erroneous condition that +//! does not come from another [`Error`](std::error::Error) (for example an +//! invalid argument). +//! +//! On top of implementing [`std::error::Error`], [`Error`] provides functions +//! to simplify conversion between [`Result<>`](std::result::Result) and +//! C `Error**` conventions. In particular: +//! +//! * [`ok_or_propagate`](qemu_api::Error::ok_or_propagate), +//! [`bool_or_propagate`](qemu_api::Error::bool_or_propagate), +//! [`ptr_or_propagate`](qemu_api::Error::ptr_or_propagate) can be used to +//! build a C return value while also propagating an error condition +//! +//! * [`err_or_else`](qemu_api::Error::err_or_else) and +//! [`err_or_unit`](qemu_api::Error::err_or_unit) can be used to build a +//! `Result` +//! +//! While these facilities are useful at the boundary between C and Rust code, +//! other Rust code need not care about the existence of this module; it can +//! just use the [`qemu_api::Result`] type alias and rely on the `?` operator as +//! usual. +//! +//! @author Paolo Bonzini + +use std::{ + borrow::Cow, + ffi::{c_char, c_int, c_void, CStr}, + fmt::{self, Display}, + panic, ptr, +}; + +use foreign::{prelude::*, OwnedPointer}; + +use crate::bindings; + +pub type Result<T> = std::result::Result<T, Error>; + +#[derive(Debug)] +pub struct Error { + msg: Option<Cow<'static, str>>, + /// Appends the print string of the error to the msg if not None + cause: Option<anyhow::Error>, + file: &'static str, + line: u32, +} + +impl std::error::Error for Error { + fn source(&self) -> Option<&(dyn std::error::Error + 'static)> { + self.cause.as_ref().map(AsRef::as_ref) + } + + #[allow(deprecated)] + fn description(&self) -> &str { + self.msg + .as_deref() + .or_else(|| self.cause.as_deref().map(std::error::Error::description)) + .unwrap_or("unknown error") + } +} + +impl Display for Error { + fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { + let mut prefix = ""; + if let Some(ref msg) = self.msg { + write!(f, "{msg}")?; + prefix = ": "; + } + if let Some(ref cause) = self.cause { + write!(f, "{prefix}{cause}")?; + } else if prefix.is_empty() { + f.write_str("unknown error")?; + } + Ok(()) + } +} + +impl From<String> for Error { + #[track_caller] + fn from(msg: String) -> Self { + let location = panic::Location::caller(); + Error { + msg: Some(Cow::Owned(msg)), + cause: None, + file: location.file(), + line: location.line(), + } + } +} + +impl From<&'static str> for Error { + #[track_caller] + fn from(msg: &'static str) -> Self { + let location = panic::Location::caller(); + Error { + msg: Some(Cow::Borrowed(msg)), + cause: None, + file: location.file(), + line: location.line(), + } + } +} + +impl From<anyhow::Error> for Error { + #[track_caller] + fn from(error: anyhow::Error) -> Self { + let location = panic::Location::caller(); + Error { + msg: None, + cause: Some(error), + file: location.file(), + line: location.line(), + } + } +} + +impl Error { + /// Create a new error, prepending `msg` to the + /// description of `cause` + #[track_caller] + pub fn with_error(msg: impl Into<Cow<'static, str>>, cause: impl Into<anyhow::Error>) -> Self { + let location = panic::Location::caller(); + Error { + msg: Some(msg.into()), + cause: Some(cause.into()), + file: location.file(), + line: location.line(), + } + } + + /// Consume a result, returning `false` if it is an error and + /// `true` if it is successful. The error is propagated into + /// `errp` like the C API `error_propagate` would do. + /// + /// # Safety + /// + /// `errp` must be a valid argument to `error_propagate`; + /// typically it is received from C code and need not be + /// checked further at the Rust↔C boundary. + pub unsafe fn bool_or_propagate(result: Result<()>, errp: *mut *mut bindings::Error) -> bool { + // SAFETY: caller guarantees errp is valid + unsafe { Self::ok_or_propagate(result, errp) }.is_some() + } + + /// Consume a result, returning a `NULL` pointer if it is an + /// error and a C representation of the contents if it is + /// successful. The error is propagated into `errp` like + /// the C API `error_propagate` would do. + /// + /// # Safety + /// + /// `errp` must be a valid argument to `error_propagate`; + /// typically it is received from C code and need not be + /// checked further at the Rust↔C boundary. + #[must_use] + pub unsafe fn ptr_or_propagate<T: CloneToForeign>( + result: Result<T>, + errp: *mut *mut bindings::Error, + ) -> *mut T::Foreign { + // SAFETY: caller guarantees errp is valid + unsafe { Self::ok_or_propagate(result, errp) }.clone_to_foreign_ptr() + } + + /// Consume a result in the same way as `self.ok()`, but also propagate + /// a possible error into `errp`, like the C API `error_propagate` + /// would do. + /// + /// # Safety + /// + /// `errp` must be a valid argument to `error_propagate`; + /// typically it is received from C code and need not be + /// checked further at the Rust↔C boundary. + pub unsafe fn ok_or_propagate<T>( + result: Result<T>, + errp: *mut *mut bindings::Error, + ) -> Option<T> { + result.map_err(|err| unsafe { err.propagate(errp) }).ok() + } + + /// Equivalent of the C function `error_propagate`. Fill `*errp` + /// with the information container in `self` if `errp` is not NULL; + /// then consume it. + /// + /// # Safety + /// + /// `errp` must be a valid argument to `error_propagate`; + /// typically it is received from C code and need not be + /// checked further at the Rust↔C boundary. + pub unsafe fn propagate(self, errp: *mut *mut bindings::Error) { + if errp.is_null() { + return; + } + + let err = self.clone_to_foreign_ptr(); + + // SAFETY: caller guarantees errp is valid + unsafe { + errp.write(err); + } + } + + /// Convert a C `Error*` into a Rust `Result`, using + /// `Ok(())` if `c_error` is NULL. Free the `Error*`. + /// + /// # Safety + /// + /// `c_error` must be `NULL` or valid; typically it was initialized + /// with `ptr::null_mut()` and passed by reference to a C function. + pub unsafe fn err_or_unit(c_error: *mut bindings::Error) -> Result<()> { + // SAFETY: caller guarantees c_error is valid + unsafe { Self::err_or_else(c_error, || ()) } + } + + /// Convert a C `Error*` into a Rust `Result`, calling `f()` to + /// obtain an `Ok` value if `c_error` is NULL. Free the `Error*`. + /// + /// # Safety + /// + /// `c_error` must be `NULL` or valid; typically it was initialized + /// with `ptr::null_mut()` and passed by reference to a C function. + pub unsafe fn err_or_else<T, F: FnOnce() -> T>( + c_error: *mut bindings::Error, + f: F, + ) -> Result<T> { + // SAFETY: caller guarantees c_error is valid + let err = unsafe { Option::<Self>::from_foreign(c_error) }; + match err { + None => Ok(f()), + Some(err) => Err(err), + } + } +} + +impl FreeForeign for Error { + type Foreign = bindings::Error; + + unsafe fn free_foreign(p: *mut bindings::Error) { + // SAFETY: caller guarantees p is valid + unsafe { + bindings::error_free(p); + } + } +} + +impl CloneToForeign for Error { + fn clone_to_foreign(&self) -> OwnedPointer<Self> { + // SAFETY: all arguments are controlled by this function + unsafe { + let err: *mut c_void = libc::malloc(std::mem::size_of::<bindings::Error>()); + let err: &mut bindings::Error = &mut *err.cast(); + *err = bindings::Error { + msg: format!("{self}").clone_to_foreign_ptr(), + err_class: bindings::ERROR_CLASS_GENERIC_ERROR, + src_len: self.file.len() as c_int, + src: self.file.as_ptr().cast::<c_char>(), + line: self.line as c_int, + func: ptr::null_mut(), + hint: ptr::null_mut(), + }; + OwnedPointer::new(err) + } + } +} + +impl FromForeign for Error { + unsafe fn cloned_from_foreign(c_error: *const bindings::Error) -> Self { + // SAFETY: caller guarantees c_error is valid + unsafe { + let error = &*c_error; + let file = if error.src_len < 0 { + // NUL-terminated + CStr::from_ptr(error.src).to_str() + } else { + // Can become str::from_utf8 with Rust 1.87.0 + std::str::from_utf8(std::slice::from_raw_parts( + &*error.src.cast::<u8>(), + error.src_len as usize, + )) + }; + + Error { + msg: FromForeign::cloned_from_foreign(error.msg), + cause: None, + file: file.unwrap(), + line: error.line as u32, + } + } + } +} diff --git a/rust/qemu-api/src/lib.rs b/rust/qemu-api/src/lib.rs index 234a94e3c29..93902fc94bc 100644 --- a/rust/qemu-api/src/lib.rs +++ b/rust/qemu-api/src/lib.rs @@ -19,6 +19,7 @@ pub mod cell; pub mod chardev; pub mod errno; +pub mod error; pub mod irq; pub mod memory; pub mod module; @@ -34,6 +35,8 @@ ffi::c_void, }; +pub use error::{Error, Result}; + #[cfg(HAVE_GLIB_WITH_ALIGNED_ALLOC)] extern "C" { fn g_aligned_alloc0( -- 2.49.0
