Messages in this thread | | | Subject | Re: unionfs | Date | Mon, 15 Mar 2004 15:22:41 -0400 | From | Horst von Brand <> |
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=?iso-8859-1?Q?J=F6rn?= Engel <joern@wohnheim.fh-wedel.de> said: > On Mon, 15 March 2004 22:35:20 +0800, Ian Kent wrote:
> > I don't understand the requirement properly. Sorry.
> Depends on who you ask, but imo it boils down to this: > - Use one filesystem as backing store, usually ro. > - Have another filesystem on top for extra functionality, usually rw > access. > > Famous example is a rw-CDROM, where writes go to hard drive and > unchanged data is read from CDROM. But it makes sense for other > things as well.
And what if the underlying filesystem is RW too? What should happen if you unite several (>= 3) filesystems? What if some are RO, others RW? What do you do if a file shows up several times, each different?
Assuming one RW on top of a RO only now: What should happen when a file/directory is missing from the top? If the bottom one "shows through", you can't delete anything; if it doesn't, you win nothing (because you will have to keep a complete copy RW on top).
IIRC, this has been discussed a couple of times before, and the consensus each time was that it isn't /that hard/ to do, it is /hard or impossible/ to find a sensible, simple semantics for this. The idea was then dropped... -- Dr. Horst H. von Brand User #22616 counter.li.org Departamento de Informatica Fono: +56 32 654431 Universidad Tecnica Federico Santa Maria +56 32 654239 Casilla 110-V, Valparaiso, Chile Fax: +56 32 797513
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