206 lines
6.5 KiB
Rust
206 lines
6.5 KiB
Rust
// SPDX-License-Identifier: GPL-2.0
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//! Printing facilities.
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//!
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//! C header: [`include/linux/printk.h`](../../../../include/linux/printk.h)
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//!
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//! Reference: <https://www.kernel.org/doc/html/latest/core-api/printk-basics.html>
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use core::{
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ffi::{c_char, c_void},
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fmt,
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};
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use crate::str::RawFormatter;
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#[cfg(CONFIG_PRINTK)]
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use crate::bindings;
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// Called from `vsprintf` with format specifier `%pA`.
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#[no_mangle]
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unsafe fn rust_fmt_argument(buf: *mut c_char, end: *mut c_char, ptr: *const c_void) -> *mut c_char {
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use fmt::Write;
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// SAFETY: The C contract guarantees that `buf` is valid if it's less than `end`.
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let mut w = unsafe { RawFormatter::from_ptrs(buf.cast(), end.cast()) };
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let _ = w.write_fmt(unsafe { *(ptr as *const fmt::Arguments<'_>) });
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w.pos().cast()
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}
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/// Format strings.
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///
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/// Public but hidden since it should only be used from public macros.
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#[doc(hidden)]
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pub mod format_strings {
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use crate::bindings;
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/// The length we copy from the `KERN_*` kernel prefixes.
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const LENGTH_PREFIX: usize = 2;
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/// The length of the fixed format strings.
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pub const LENGTH: usize = 10;
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/// Generates a fixed format string for the kernel's [`_printk`].
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///
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/// The format string is always the same for a given level, i.e. for a
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/// given `prefix`, which are the kernel's `KERN_*` constants.
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///
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/// [`_printk`]: ../../../../include/linux/printk.h
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const fn generate(is_cont: bool, prefix: &[u8; 3]) -> [u8; LENGTH] {
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// Ensure the `KERN_*` macros are what we expect.
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assert!(prefix[0] == b'\x01');
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if is_cont {
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assert!(prefix[1] == b'c');
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} else {
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assert!(prefix[1] >= b'0' && prefix[1] <= b'7');
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}
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assert!(prefix[2] == b'\x00');
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let suffix: &[u8; LENGTH - LENGTH_PREFIX] = if is_cont {
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b"%pA\0\0\0\0\0"
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} else {
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b"%s: %pA\0"
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};
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[
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prefix[0], prefix[1], suffix[0], suffix[1], suffix[2], suffix[3], suffix[4], suffix[5],
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suffix[6], suffix[7],
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]
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}
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// Generate the format strings at compile-time.
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//
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// This avoids the compiler generating the contents on the fly in the stack.
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//
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// Furthermore, `static` instead of `const` is used to share the strings
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// for all the kernel.
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pub static EMERG: [u8; LENGTH] = generate(false, bindings::KERN_EMERG);
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pub static INFO: [u8; LENGTH] = generate(false, bindings::KERN_INFO);
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}
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/// Prints a message via the kernel's [`_printk`].
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///
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/// Public but hidden since it should only be used from public macros.
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///
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/// # Safety
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///
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/// The format string must be one of the ones in [`format_strings`], and
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/// the module name must be null-terminated.
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///
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/// [`_printk`]: ../../../../include/linux/_printk.h
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#[doc(hidden)]
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#[cfg_attr(not(CONFIG_PRINTK), allow(unused_variables))]
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pub unsafe fn call_printk(
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format_string: &[u8; format_strings::LENGTH],
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module_name: &[u8],
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args: fmt::Arguments<'_>,
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) {
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// `_printk` does not seem to fail in any path.
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#[cfg(CONFIG_PRINTK)]
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unsafe {
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bindings::_printk(
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format_string.as_ptr() as _,
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module_name.as_ptr(),
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&args as *const _ as *const c_void,
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);
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}
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}
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/// Performs formatting and forwards the string to [`call_printk`].
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///
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/// Public but hidden since it should only be used from public macros.
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#[doc(hidden)]
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#[cfg(not(testlib))]
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#[macro_export]
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#[allow(clippy::crate_in_macro_def)]
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macro_rules! print_macro (
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// The non-continuation cases (most of them, e.g. `INFO`).
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($format_string:path, $($arg:tt)+) => (
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// To remain sound, `arg`s must be expanded outside the `unsafe` block.
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// Typically one would use a `let` binding for that; however, `format_args!`
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// takes borrows on the arguments, but does not extend the scope of temporaries.
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// Therefore, a `match` expression is used to keep them around, since
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// the scrutinee is kept until the end of the `match`.
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match format_args!($($arg)+) {
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// SAFETY: This hidden macro should only be called by the documented
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// printing macros which ensure the format string is one of the fixed
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// ones. All `__LOG_PREFIX`s are null-terminated as they are generated
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// by the `module!` proc macro or fixed values defined in a kernel
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// crate.
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args => unsafe {
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$crate::print::call_printk(
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&$format_string,
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crate::__LOG_PREFIX,
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args,
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);
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}
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}
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);
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);
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/// Stub for doctests
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#[cfg(testlib)]
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#[macro_export]
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macro_rules! print_macro (
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($format_string:path, $e:expr, $($arg:tt)+) => (
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()
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);
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);
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// We could use a macro to generate these macros. However, doing so ends
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// up being a bit ugly: it requires the dollar token trick to escape `$` as
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// well as playing with the `doc` attribute. Furthermore, they cannot be easily
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// imported in the prelude due to [1]. So, for the moment, we just write them
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// manually, like in the C side; while keeping most of the logic in another
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// macro, i.e. [`print_macro`].
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//
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// [1]: https://github.com/rust-lang/rust/issues/52234
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/// Prints an emergency-level message (level 0).
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///
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/// Use this level if the system is unusable.
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///
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/// Equivalent to the kernel's [`pr_emerg`] macro.
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///
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/// Mimics the interface of [`std::print!`]. See [`core::fmt`] and
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/// `alloc::format!` for information about the formatting syntax.
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///
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/// [`pr_emerg`]: https://www.kernel.org/doc/html/latest/core-api/printk-basics.html#c.pr_emerg
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/// [`std::print!`]: https://doc.rust-lang.org/std/macro.print.html
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///
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/// # Examples
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///
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/// ```
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/// pr_emerg!("hello {}\n", "there");
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/// ```
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#[macro_export]
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macro_rules! pr_emerg (
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($($arg:tt)*) => (
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$crate::print_macro!($crate::print::format_strings::EMERG, $($arg)*)
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)
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);
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/// Prints an info-level message (level 6).
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///
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/// Use this level for informational messages.
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///
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/// Equivalent to the kernel's [`pr_info`] macro.
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///
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/// Mimics the interface of [`std::print!`]. See [`core::fmt`] and
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/// `alloc::format!` for information about the formatting syntax.
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///
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/// [`pr_info`]: https://www.kernel.org/doc/html/latest/core-api/printk-basics.html#c.pr_info
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/// [`std::print!`]: https://doc.rust-lang.org/std/macro.print.html
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///
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/// # Examples
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///
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/// ```
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/// pr_info!("hello {}\n", "there");
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/// ```
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#[macro_export]
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#[doc(alias = "print")]
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macro_rules! pr_info (
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($($arg:tt)*) => (
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$crate::print_macro!($crate::print::format_strings::INFO, $($arg)*)
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)
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);
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