Man page 9 : lock_may_read

lock_may_read - checks that the region is free of locks

int lock_may_read(struct inode *  inode , loff_t  start , unsigned long  len );

inode
    the inode that is being read

start
    the first byte to read

len
    the number of bytes to read

Emulates Windows locking requirements. Whole-file mandatory locks (share modes) can prohibit a read and byte-range POSIX locks can prohibit a read if they overlap.

N.B. this function is only ever called from knfsd and ownership of locks is never checked.