Re: [RFC] readlink()-related oddities

[Al Viro <viro@ZenIV.linux.org.uk>]

On Fri, Nov 20, 2015 at 09:59:05AM +0000, David Howells wrote:

> There's an AFS userspace command that could be used to query a mountpoint that
> was going to use it.  However, I suspect readlink() will now always trigger
> the automount.

It won't, actually.  All we are passing to user_path_at_empty() is
LOOKUP_EMPTY, so for the final component we'll have
        if (!(nd->flags & (LOOKUP_PARENT | LOOKUP_DIRECTORY |
                           LOOKUP_OPEN | LOOKUP_CREATE | LOOKUP_AUTOMOUNT)) &&
            path->dentry->d_inode)
                return -EISDIR;
in follow_automount() trigger and follow_managed() will turn that -EISDIR
into 0.  IOW, readlink(2) does work on those, same as stat() (since Sep 2011).

Sigh...  OK, let's leave it for now; ->open() for those guys is completely
bogus, AFAICS, but that's local bogo^Wbusiness.