Fix suseconds_t type signedness for Linux ABI compatibility

[wdcui]

Summary

The suseconds_t type is defined as unsigned (u32/u64) but should be signed (i32/i64) per Linux kernel ABI.

Location

litebox_common_linux/src/lib.rs lines 771-781:

cfg_if::cfg_if! {
    if #[cfg(all(target_arch = "x86"))] {
        pub type time_t = i32;
        pub type suseconds_t = u32;  // <-- Should be i32
    } else if #[cfg(all(target_arch = "x86_64"))] {
        pub type time_t = i64;
        pub type suseconds_t = u64;  // <-- Should be i64
    } else {
        compile_error!("Unsupported architecture");
    }
}

Expected Behavior

Per Linux kernel (include/uapi/asm-generic/posix_types.h):

typedef __kernel_long_t    __kernel_suseconds_t;

Where __kernel_long_t is long (signed). So:

• On x86 (32-bit): suseconds_t should be i32
• On x86_64 (64-bit): suseconds_t should be i64

Impact

This affects the TimeVal struct which is used in:

• Rusage.ru_utime and Rusage.ru_stime (getrusage syscall)
• ItimerVal (setitimer/getitimer syscalls)
• Any other syscalls using TimeVal

Current impact is minimal since:

1. suseconds_t values are typically non-negative microseconds (0-999999)
2. Current implementations return zeroed values

However, for strict ABI compatibility and future implementations that populate real time values, this should be fixed.

Suggested Fix

cfg_if::cfg_if! {
    if #[cfg(all(target_arch = "x86"))] {
        pub type time_t = i32;
        pub type suseconds_t = i32;  // Changed from u32
    } else if #[cfg(all(target_arch = "x86_64"))] {
        pub type time_t = i64;
        pub type suseconds_t = i64;  // Changed from u64
    } else {
        compile_error!("Unsupported architecture");
    }
}

Additional Consideration

Consider adding compile-time size assertions for structs that depend on these types:

#[cfg(target_arch = "x86_64")]
const _: () = assert!(core::mem::size_of::<TimeVal>() == 16);
#[cfg(target_arch = "x86")]
const _: () = assert!(core::mem::size_of::<TimeVal>() == 8);

Found During

Code review of PR #606 (getrusage syscall implementation).