ulib: Add a very basic rust library

Create a new lib/rust directory and add a very basic rust library in
there. This will eventually expand to include more features. For now
it only has a few ulib calls needed for the example programs.

Co-developed-by: Claude <noreply@anthropic.com>
Co-developed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>

lib/rust/.gitignore

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+target/

lib/rust/Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
+[[package]]
+name = "uboot-sys"
+version = "0.1.0"

lib/rust/Cargo.toml

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+# SPDX-License-Identifier: GPL-2.0+
+[package]
+name = "u-boot-sys"
+version = "0.1.0"
+edition = "2021"
+license = "GPL-2.0+"
+description = "Rust FFI bindings for U-Boot library functions"
+authors = ["Simon Glass <simon.glass@canonical.com>"]
+repository = "https://concept.u-boot.org/u-boot/u-boot"
+keywords = ["u-boot", "ffi", "bindings", "embedded"]
+categories = ["external-ffi-bindings", "embedded"]
+
+[lib]
+name = "u_boot_sys"
+path = "src/lib.rs"
+
+[dependencies]

lib/rust/src/lib.rs

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+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * U-Boot FFI bindings for Rust
+ *
+ * This crate provides Rust FFI bindings for U-Boot library functions,
+ * equivalent to include/u-boot-lib.h
+ *
+ * Copyright 2025 Canonical Ltd.
+ * Written by Simon Glass <simon.glass@canonical.com>
+ */
+
+//! # U-Boot Bindings
+//!
+//! This crate provides Rust FFI bindings for U-Boot library functions.
+//! It includes bindings for:
+//!
+//! - U-Boot library management functions (`ulib_*`)
+//! - U-Boot API functions (`ub_*`)
+//! - OS abstraction functions (`os_*`)
+//!
+//! ## Usage
+//!
+//! ```rust,no_run
+//! use uboot_sys::{ulib_init, ulib_uninit, ub_printf};
+//! use std::ffi::CString;
+//!
+//! let program_name = CString::new("my_program").unwrap();
+//! unsafe {
+//!     if ulib_init(program_name.as_ptr() as *mut _) == 0 {
+//!         ub_printf(b"Hello from U-Boot!\n\0".as_ptr() as *const _);
+//!         ulib_uninit();
+//!     }
+//! }
+//! ```
+
+#![allow(clippy::manual_c_str_literals)]
+#![allow(non_camel_case_types)]
+
+use std::os::raw::{c_char, c_int};
+
+/// U-Boot library management functions
+pub mod uboot_lib {
+    use super::*;
+
+    extern "C" {
+        /// Set up the U-Boot library
+        ///
+        /// # Arguments
+        ///
+        /// * `progname` - Program name to use (must be a writeable string,
+        ///                typically argv\[0\])
+        ///
+        /// # Returns
+        ///
+        /// 0 if OK, negative error code on error
+        pub fn ulib_init(progname: *mut c_char) -> c_int;
+
+        /// Shut down the U-Boot library
+        ///
+        /// Call this when your program has finished using the library,
+        /// before it exits
+        pub fn ulib_uninit();
+
+        /// Get the version string
+        ///
+        /// # Returns
+        ///
+        /// Full U-Boot version string
+        pub fn ulib_get_version() -> *const c_char;
+    }
+}
+
+/// U-Boot API functions
+pub mod uboot_api {
+    use super::*;
+
+    extern "C" {
+        /// Print directly to console (equivalent to printf)
+        ///
+        /// # Arguments
+        ///
+        /// * `fmt` - The format string to use
+        /// * `...` - Arguments for the format string
+        ///
+        /// # Returns
+        ///
+        /// Number of characters printed
+        pub fn ub_printf(fmt: *const c_char, ...) -> c_int;
+
+        /// Format a string and place it in a buffer
+        ///
+        /// # Arguments
+        ///
+        /// * `buf` - The buffer to place the result into
+        /// * `size` - The size of the buffer, including the trailing null
+        ///            space
+        /// * `fmt` - The format string to use
+        /// * `...` - Arguments for the format string
+        ///
+        /// # Returns
+        ///
+        /// The number of characters which would be generated for the given
+        /// input, excluding the trailing null, as per ISO C99
+        pub fn ub_snprintf(
+            buf: *mut c_char,
+            size: usize,
+            fmt: *const c_char,
+            ...
+        ) -> c_int;
+
+        /// Format a string and place it in a buffer
+        ///
+        /// # Arguments
+        ///
+        /// * `buf` - The buffer to place the result into
+        /// * `fmt` - The format string to use
+        /// * `...` - Arguments for the format string
+        ///
+        /// # Returns
+        ///
+        /// The number of characters written into buf
+        pub fn ub_sprintf(buf: *mut c_char, fmt: *const c_char, ...) -> c_int;
+    }
+}
+
+/// OS abstraction functions
+pub mod os {
+    use super::*;
+
+    extern "C" {
+        /// Access the OS open() system call
+        ///
+        /// # Arguments
+        ///
+        /// * `pathname` - Path to the file to open
+        /// * `flags` - Open flags
+        ///
+        /// # Returns
+        ///
+        /// File descriptor, or negative error code on error
+        pub fn os_open(pathname: *const c_char, flags: c_int) -> c_int;
+
+        /// Access the OS close() system call
+        ///
+        /// # Arguments
+        ///
+        /// * `fd` - File descriptor to close
+        ///
+        /// # Returns
+        ///
+        /// 0 on success, negative error code on error
+        pub fn os_close(fd: c_int) -> c_int;
+
+        /// Read a string from a file stream
+        ///
+        /// # Arguments
+        ///
+        /// * `s` - Buffer to store the string
+        /// * `size` - Maximum number of characters to read
+        /// * `fd` - File descriptor to read from
+        ///
+        /// # Returns
+        ///
+        /// Pointer to the string on success, null pointer on EOF or
+        /// error
+        pub fn os_fgets(s: *mut c_char, size: c_int, fd: c_int) -> *mut c_char;
+    }
+}
+
+// Re-export commonly used functions at crate root
+pub use uboot_lib::{ulib_get_version, ulib_init, ulib_uninit};
+pub use uboot_api::{ub_printf, ub_snprintf, ub_sprintf};
+pub use os::{os_close, os_fgets, os_open};