armybox 0.3.0

A memory-safe #[no_std] BusyBox/Toybox clone in Rust - 299 Unix utilities in ~500KB
Documentation 
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//! pivot_root - change the root filesystem
//!
//! Move the root filesystem to a new location.

use crate::io;
use crate::sys;
use crate::applets::get_arg;

/// pivot_root - change the root filesystem
///
/// # Synopsis
/// ```text
/// pivot_root new_root put_old
/// ```
///
/// # Description
/// Move the root filesystem of the calling process to the directory put_old
/// and make new_root the new root filesystem.
///
/// # Exit Status
/// - 0: Success
/// - 1: Error
pub fn pivot_root(argc: i32, argv: *const *const u8) -> i32 {
    if argc < 3 {
        io::write_str(2, b"pivot_root: usage: pivot_root new_root put_old\n");
        return 1;
    }

    let new_root = unsafe { get_arg(argv, 1).unwrap() };
    let put_old = unsafe { get_arg(argv, 2).unwrap() };

    // Create null-terminated strings
    let mut new_root_buf = [0u8; 4096];
    let mut put_old_buf = [0u8; 4096];

    new_root_buf[..new_root.len()].copy_from_slice(new_root);
    put_old_buf[..put_old.len()].copy_from_slice(put_old);

    // Call pivot_root syscall
    if unsafe {
        libc::syscall(
            libc::SYS_pivot_root,
            new_root_buf.as_ptr(),
            put_old_buf.as_ptr(),
        )
    } != 0
    {
        sys::perror(b"pivot_root");
        return 1;
    }

    0
}

#[cfg(test)]
mod tests {
    extern crate std;
    use std::process::Command;
    use std::path::PathBuf;

    fn get_armybox_path() -> PathBuf {
        if let Ok(path) = std::env::var("ARMYBOX_PATH") {
            return PathBuf::from(path);
        }
        let manifest_dir = std::env::var("CARGO_MANIFEST_DIR")
            .map(PathBuf::from)
            .unwrap_or_else(|_| std::env::current_dir().unwrap());
        let release = manifest_dir.join("target/release/armybox");
        if release.exists() { return release; }
        manifest_dir.join("target/debug/armybox")
    }

    #[test]
    fn test_pivot_root_no_args() {
        let armybox = get_armybox_path();
        if !armybox.exists() { return; }

        let output = Command::new(&armybox)
            .args(["pivot_root"])
            .output()
            .unwrap();

        assert_eq!(output.status.code(), Some(1));
        let stderr = std::string::String::from_utf8_lossy(&output.stderr);
        assert!(stderr.contains("usage"));
    }

    #[test]
    fn test_pivot_root_invalid() {
        let armybox = get_armybox_path();
        if !armybox.exists() { return; }

        // Should fail with invalid paths (needs root and proper setup)
        let output = Command::new(&armybox)
            .args(["pivot_root", "/nonexistent", "/also_nonexistent"])
            .output()
            .unwrap();

        assert_eq!(output.status.code(), Some(1));
    }
}