Subject: Re: multiple mounts on same directory
To: None <>
From: Alan Barrett <>
List: tech-userlevel
Date: 07/18/2003 19:19:47
On Fri, 18 Jul 2003, Bill Studenmund wrote:
> I think it's perfectly fine to just have the code in mount know that for
> mfs mount (and mfs mounts _only_), f_mntfromname doesn't matter for
> differences.
> The reason that "union" is special is that if you mount with the -b
> option, then the f_mntfromname will get changed. As I recall, it'll become
> "<below>:" in front of the name. So the matching code would also need to
> synthesize a new union f_mntfromname. But once it's done that, it will
> match perfectly well.

The special cases that I know about so far are:

    fstype       original name   f_mntfromname
    ------       -------------   -------------
    mfs          anything        mfs:123
    kernfs       anything        kernfs
    procfs       anything        procfs
    union        /some/dir       <above>:/some/dir
    union        /some/dir       <below>:/some/dir
Is it OK to hard-code knowledge of these special cases in the duplicate
detection part of "mount -a"?  The normal case would then be that
f_mntfromname would have to be an exact match before a potential mount
would be detected as a duplicate.

--apb (Alan Barrett)