Emmanuel Dreyfus <m...@netbsd.org> wrote: > Now let us see the locking scenario: > - process 1 opens file foo O_RDWR > - process 2 opens file foo O_RDWR|O_NONBLOCK > - process 1 locks a part of the file > - process 2 atteemps to write to the locked part > > With advisory locks (what we have in our filesystems), the code above > VFS has no reason to block process 2 write operation. The filesystem > could notice there is a lock on the written area, but it cannot enforce > it because it does not distinguish the file descriptors. Hence the write > on locked area succeeds, but this is not a huge problem since the > locks are adivsory. > > With mandatory locks, the filesystem must block process 2 when it > writes.
The word "block" is unfortunate here: I meant the filesystem must deny process 2 when it attempts to write. Since process 2 used O_NONBLOCK, this means write() must return with EAGAIN. -- Emmanuel Dreyfus http://hcpnet.free.fr/pubz m...@netbsd.org
