• Alexander Viro's avatar
    [PATCH] removal of LOOKUP_POSITIVE · 2dee55cd
    Alexander Viro authored
    	LOOKUP_POSITIVE is not needed anymore.  All callers of path_walk()
    treat -ENOENT and negative dentry the same way.  If you want a proof of
    correctness - I'll send it, but it's a couple of pages of induction, basically
    boiling down to "let's show that for any N we can replace the
                   if (lookup_flags & (LOOKUP_POSITIVE|LOOKUP_DIRECTORY))
                           break;
    in link_path_walk() with
                   if ((lookup_flags & (LOOKUP_POSITIVE|LOOKUP_DIRECTORY)) ||
    		   current->link_count <= N)
                           break;
    without changing behaviour of the system".  Pretty straightforward for
    N = 0, then we look for places that can lead to call link_path_walk()
    with current->link_count equal to N and show that if result of the test
    changes, behaviour of callers doesn't.  Since the depth of recursion is
    limited, we had shown that test in question can be replaced with if (1).
    And that's the only place in tree the ever checks for LOOKUP_POSITIVE.
    
    	The real reason behind that is very simple - indeed, suppose
    we get a negative dentry out of path_walk().  What the hell could we
    do with it?  Its parent isn't locked, so both the name and parent can
    change at any moment (could have changed already).  There used to be
    places that tried to play "let's get a negative dentry, lock its parent
    and start doing something".  All of them racy and all of them fixed
    in 2.3.  Fixed by switching to LOOKUP_PARENT...
    2dee55cd
exec.c 22.2 KB