Function pread_exact

block/src/qcow_common.rs:26–47

Read exactly the requested bytes at offset, looping on short reads.

(fd: RawFd, buf: &mut [u8], offset: u64)

/// Read exactly the requested bytes at offset, looping on short reads.
pub fn pread_exact(fd: RawFd, buf: &mut [u8], offset: u64) -> io::Result<()> {
    let mut total = 0usize;
    while total < buf.len() {
        // SAFETY: buf and fd are valid for the lifetime of the call.
        let ret = unsafe {
            libc::pread64(
                fd,
                buf[total..].as_mut_ptr().cast(),
                buf.len() - total,
                (offset + total as u64) as libc::off_t,
            )
        };
        if ret < 0 {
            return Err(io::Error::last_os_error());
        }
        if ret == 0 {
            return Err(io::Error::from(io::ErrorKind::UnexpectedEof));
        }
        total += ret as usize;
    }
    Ok(())
}

/// Allocate a buffer and pread exactly `len` bytes at `offset`.
pub fn pread_alloc(fd: RawFd, offset: u64, len: usize) -> io::Result<Vec<u8>> {