Function fcntl::is_file_locked

pub fn is_file_locked<'a, RF>(
    fd: &'a RF, 
    flock: Option<flock>
) -> Result<bool, FcntlError> where
    RF: AsRawFd, 

Checks whether the given file is locked.

The caller is responsible that fd was opened with the appropriate parameters, as stated by fcntl (2):

In order to place a read lock, fd must be open for reading. In order to place a write lock, fd must be open for writing. To place both types of lock, open a file read-write.

use std::fs::OpenOptions;
use fcntl::is_file_locked;

let file = OpenOptions::new().read(true).open(file_name).unwrap();
match is_file_locked(&file, None) {
    Ok(true) => println!("File is currently locked"),
    Ok(false) => println!("File is not locked"),
    Err(err) => println!("Error: {:?}", err),
}