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+// Copyright 2025 Bernhard Beschow <shentey@gmail.com>
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+//! Bindings for QEMU's logging infrastructure
+
+use std::{
+ io::{self, Write},
+ ptr::NonNull,
+};
+
+use crate::{bindings, errno};
+
+#[repr(u32)]
+/// Represents specific error categories within QEMU's logging system.
+///
+/// The `Log` enum provides a Rust abstraction for logging errors, corresponding
+/// to a subset of the error categories defined in the C implementation.
+pub enum Log {
+ /// Log invalid access caused by the guest.
+ /// Corresponds to `LOG_GUEST_ERROR` in the C implementation.
+ GuestError = bindings::LOG_GUEST_ERROR,
+
+ /// Log guest access of unimplemented functionality.
+ /// Corresponds to `LOG_UNIMP` in the C implementation.
+ Unimp = bindings::LOG_UNIMP,
+}
+
+/// A RAII guard for QEMU's logging infrastructure. Creating the guard
+/// locks the log file, and dropping it (letting it go out of scope) unlocks
+/// the file.
+///
+/// As long as the guard lives, it can be written to using [`std::io::Write`].
+///
+/// The locking is recursive, therefore owning a guard does not prevent
+/// using [`log_mask_ln!()`](crate::log_mask_ln).
+pub struct LogGuard(NonNull<bindings::FILE>);
+
+impl LogGuard {
+ /// Return a RAII guard that writes to QEMU's logging infrastructure.
+ /// The log file is locked while the guard exists, ensuring that there
+ /// is no tearing of the messages.
+ ///
+ /// Return `None` if the log file is closed and could not be opened.
+ /// Do *not* use `unwrap()` on the result; failure can be handled simply
+ /// by not logging anything.
+ ///
+ /// # Examples
+ ///
+ /// ```
+ /// # use qemu_api::log::LogGuard;
+ /// # use std::io::Write;
+ /// if let Some(mut log) = LogGuard::new() {
+ /// writeln!(log, "test");
+ /// }
+ /// ```
+ pub fn new() -> Option<Self> {
+ let f = unsafe { bindings::qemu_log_trylock() }.cast();
+ NonNull::new(f).map(Self)
+ }
+
+ /// Writes a formatted string into the log, returning any error encountered.
+ ///
+ /// This method is primarily used by the
+ /// [`log_mask_ln!()`](crate::log_mask_ln) macro, and it is rare for it
+ /// to be called explicitly. It is public because it is the only way to
+ /// examine the error, which `log_mask_ln!()` ignores
+ ///
+ /// Unlike `log_mask_ln!()`, it does *not* append a newline at the end.
+ pub fn log_fmt(args: std::fmt::Arguments) -> io::Result<()> {
+ if let Some(mut log) = Self::new() {
+ log.write_fmt(args)?;
+ }
+ Ok(())
+ }
+}
+
+impl Write for LogGuard {
+ fn write(&mut self, bytes: &[u8]) -> io::Result<usize> {
+ let ret = unsafe {
+ bindings::rust_fwrite(bytes.as_ptr().cast(), 1, bytes.len(), self.0.as_ptr())
+ };
+ errno::into_io_result(ret)
+ }
+
+ fn flush(&mut self) -> io::Result<()> {
+ // Do nothing, dropping the guard takes care of flushing
+ Ok(())
+ }
+}
+
+impl Drop for LogGuard {
+ fn drop(&mut self) {
+ unsafe {
+ bindings::qemu_log_unlock(self.0.as_ptr());
+ }
+ }
+}
+
+/// A macro to log messages conditionally based on a provided mask.
+///
+/// The `log_mask_ln` macro checks whether the given mask matches the current
+/// log level and, if so, formats and logs the message. It is the Rust
+/// counterpart of the `qemu_log_mask()` macro in the C implementation.
+///
+/// Errors from writing to the log are ignored.
+///
+/// # Parameters
+///
+/// - `$mask`: A log level mask. This should be a variant of the `Log` enum.
+/// - `$fmt`: A format string following the syntax and rules of the `format!`
+/// macro. It specifies the structure of the log message.
+/// - `$args`: Optional arguments to be interpolated into the format string.
+///
+/// # Example
+///
+/// ```
+/// use qemu_api::{log::Log, log_mask_ln};
+///
+/// let error_address = 0xbad;
+/// log_mask_ln!(Log::GuestError, "Address 0x{error_address:x} out of range");
+/// ```
+///
+/// It is also possible to use printf-style formatting, as well as having a
+/// trailing `,`:
+///
+/// ```
+/// use qemu_api::{log::Log, log_mask_ln};
+///
+/// let error_address = 0xbad;
+/// log_mask_ln!(
+/// Log::GuestError,
+/// "Address 0x{:x} out of range",
+/// error_address,
+/// );
+/// ```
+#[macro_export]
+macro_rules! log_mask_ln {
+ ($mask:expr, $fmt:tt $($args:tt)*) => {{
+ // Type assertion to enforce type `Log` for $mask
+ let _: Log = $mask;
+
+ if unsafe {
+ (::qemu_api::bindings::qemu_loglevel & ($mask as std::os::raw::c_int)) != 0
+ } {
+ _ = ::qemu_api::log::LogGuard::log_fmt(
+ format_args!("{}\n", format_args!($fmt $($args)*)));
+ }
+ }};
+}