> On Wed, Nov 17, 1999 at 09:26:41PM +0000, Riley Williams wrote:
> > Basically, one facility I could use is that of being able to mount two
> > or more partitions on top of each other and have all the files from
> > all of the partitions available for reading. This is what I call a
> > transparent mount.
>
> It sounds a lot like (BSD's?) union mount.
> > 2. There must not be any name clashes between the contents of
> > the partition(s) already mounted at that point and that of
> > the root directory of the partition being transparently
> > mounted on top of it.
You'll get some problems with readdir() on root, but that's doable.
If you are going to do it - do it fast, or I'll do it myself for final
procfs split.
> Under union-mount, the upper layer holds changes to the lower layer, so
> conflict behavior is well defined: The upper layer wins.
>
> (I'm not sure about a delete of a file that exists on both layers. Is
> a 'deleted' entry stored on the upper FS layer? Hmmm.)
Yes.
> > I can see that verifying this second condition would be likely to be
> > time-consuming on some systems, so for an initial implementation, I
> > would suggest the following additional condition:
> >
> > 3. The total number of entries in the common directory, when
> > totalled from all partitions mounted thereon, must not be
> > such as to require more than one page of storage.
> >
> > Comments, please?
Uuurgh for #3 and to some degree for #2 ;-) Check how BSD folks had done
it. R/O is also overkill if you are doing union-mount. Seriously, take the
Daemon Book and check how it's done.
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