On Wed, Jan 09 2008, Christoph Hellwig wrote: > On Wed, Jan 09, 2008 at 09:52:32AM +0100, Jens Axboe wrote: > > - The file block mappings must not change while loop is using the file. > > This means that we have to ensure exclusive access to the file and > > this is the bit that is currently missing in the implementation. It > > would be nice if we could just do this via open(), ideas welcome... > > And the way this is done is simply broken. It means you have to get > rid of things like delayed or unwritten hands beforehand, it'll be > a complete pain for COW or non-block backed filesystems. COW is not that hard to handle, you just need to be notified of moving blocks. If you view the patch as just a tighter integration between loop and fs, I don't think it's necessarily that broken. I did consider these cases, and it can be done with the existing approach. > The right way to do this is to allow direct I/O from kernel sources > where the filesystem is in-charge of submitting the actual I/O after > the pages are handed to it. I think Peter Zijlstra has been looking > into something like that for swap over nfs. That does sound like a nice approach, but a lot more work. It'll behave differently too, the advantage of what I proposed is that it behaves like a real device. I'm not asking you to love it (in fact I knew some people would complain about this approach and I understand why), just tossing it out there to get things rolling. If we end up doing it differently I don't really care, I'm not married to any solution but merely wish to solve a problem. If that ends up being solved differently, the outcome is the same to me. -- Jens Axboe - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
