tg-rcore-tutorial-user 0.4.10

User-space apps for rCore Tutorial chapters (subset for ch2).
Documentation 
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#![no_std]
#![no_main]

#[macro_use]
extern crate user_lib;
extern crate alloc;

use user_lib::{close, open, read, OpenFlags};

// 教学目标：
// 实现最小版 cat，验证按块循环 read 直到 EOF 的文件读取模式。

#[unsafe(no_mangle)]
pub extern "C" fn main() -> i32 {
    let fd = open("filea\0", OpenFlags::RDONLY);
    if fd == -1 {
        panic!("Error occured when opening file");
    }
    let fd = fd as usize;
    let mut buf = [0u8; 256];
    loop {
        let size = read(fd, &mut buf) as usize;
        if size == 0 {
            break;
        }
        println!("{}", core::str::from_utf8(&buf[..size]).unwrap());
    }
    close(fd);
    0
}