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SubjectRe: Loop Devices over NFS don't work?
Hi!

> > > You could fall back to read/write in theory. There is an interesting project
> > > for you 8)
> >
> > Really? Think about deadlocks. Both nbd and loop are _evil_. Mount
> > sparse file over loopback, then write to both filessytems in heavy way
> > to see why. THIS IS NOT EASY.
>
> Time to embarrass myself once more on l-k ;) Intuition tells me that deadlocks
> and races need to be thought about, but unfortunately I can't see what they
> are.
>
> How is writing to a filesystem on the loopbacked device simultaneously with
> the hosting filesystem any different from writing to two files on the hosted
> filesystem simultaneously?

Because for writing _datablock_ on loopfs you need to write
_indirectblock_ on hosting filesystem. Something that could not have
happened before. And now imagine writing _indirectblock_ on loop,
which results into write of _indirectblock_ on hosting fs. I am not
telling you I understand those issues. I just see it is not easy.

> Swapping, of course, is a different issue. Do we have any flags at the moment
> which prevent people from trying to swap to inappropriate block devices (nbd,
> certain raid levels with md, etc.)?

No and I'd like to see such patch.

Pavel

--
I'm really pavel@ucw.cz. Look at http://195.113.31.123/~pavel. Pavel
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