Function try_acquire_lock

block/src/fcntl.rs:197–219

Tries to acquire a lock using [`fcntl`] with respect to the given parameters. Please note that `fcntl()` OFD locks are **advisory locks**, which do not prevent to `open()` a file if a lock is already placed. # Parameters - `file`: The file to acquire a lock for [`LockType`]. The file's state will be logically mutated, but not technically. - `lock_type`: The [`LockType`] - `granularity`: The [`Lo

(
    file: &Fd,
    lock_type: LockType,
    granularity: LockGranularity,
)

/// - `lock_type`: The [`LockType`]
/// - `granularity`: The [`LockGranularity`].
pub fn try_acquire_lock<Fd: AsRawFd>(
    file: &Fd,
    lock_type: LockType,
    granularity: LockGranularity,
) -> Result<(), LockError> {
    let flock = get_flock(lock_type, granularity);

    let res = fcntl(file.as_raw_fd(), FcntlArg::F_OFD_SETLK(&flock));
    match res {
        0 => Ok(()),
        -1 => {
            let io_error = io::Error::last_os_error();
            let errno = io_error.raw_os_error().unwrap();
            match errno {
                // See man page for error code:
                // <https://man7.org/linux/man-pages/man2/fcntl.2.html>
                libc::EAGAIN | libc::EACCES => Err(LockError::AlreadyLocked),
                _ => Err(LockError::Io(io_error)),
            }
        }
        val => panic!("Unexpected return value from fcntl(): {val}"),
    }
}

/// Clears a lock.
///