Messages in this thread | | | From | Malcolm Beattie <> | Subject | Re: Overmounting a filesystem | Date | Fri, 12 Apr 1996 17:06:27 +0100 (BST) |
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Albert Cahalan writes: > > >> mount /dev/hda2 /home > >> ... do things > >> mount /dev/hda3 /home > > > > can I do things like that: > > > > mount /dev/cdrom /cdrom > > mount /cdrom/adirectory /home/ftp/adirectory > > With Linux, I am almost sure you can not do that. > > With OSF/1 and Digital Unix, I think you can. You can mount > one file on top of another, so directories might work too.
Unfortunately they don't. It's a special filesystem type (FFM--"file on file mounting) and it lets you do two things. (1) You can mount regular files, character or block special devices on top of a file. (2) You can attach a STREAMS file descriptor to the filesystem on top of a regular file or directory with fattach(3). You can't mount directories. I played with this stuff with OSF/1 3.0 (or possibly field-test T3.0) and it created a number of panics, some of which I QAR'd and were fixed by DEC. Since I only had access to a "live" OSF/1 system with real lusers until very recently, I haven't risked trying out FFM again. It never seemed to quite live up to its potential. All the neat ideas I could think of (such as "loopback" mounting of directories and attaching ready-prepared open file descriptors to the filesystem) never seemed to work properly. Maybe most of the problems have been fixed by now, but I doubt it. I think the main reason for FFM was to support SysV fattach() and it doesn't go much further.
--Malcolm
-- Malcolm Beattie <mbeattie@sable.ox.ac.uk> Unix Systems Programmer Oxford University Computing Services
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