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Diffstat (limited to 'rust/qemu-api/src/log.rs')
-rw-r--r-- | rust/qemu-api/src/log.rs | 149 |
1 files changed, 149 insertions, 0 deletions
diff --git a/rust/qemu-api/src/log.rs b/rust/qemu-api/src/log.rs new file mode 100644 index 0000000..a441b8c --- /dev/null +++ b/rust/qemu-api/src/log.rs @@ -0,0 +1,149 @@ +// 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)*))); + } + }}; +} |