Jens Axboe <jaxboe@xxxxxxxxxxxx> writes: > On 2011-08-18 21:08, Lukas Czerner wrote: >> On Thu, 18 Aug 2011, Milan Broz wrote: >> >>> On 08/18/2011 05:49 PM, Lukas Czerner wrote: >>>> On Thu, 18 Aug 2011, Jeff Moyer wrote: >>>>> Seems you missed the bizarre case of configuring a loop device over top >>>>> of a block device. >>>> >>>> Wow, that is a bizarre case I did not think about at all. But since it >>>> is so bizarre, do we even care ? The thing is that the only case where >>>> it would make a difference is if the loop device is put on top of block >>>> device which actually supports discard. >>>> >>>> In order to fix that I would need to dig out the actual limits for that >>>> device and set that appropriately for the loop device. Is that worth it >>>> ? It is not like someone will ever do that (or should) :). >>> >>> It is bizarre (and being device-mapper developer I surely know better way :-) >>> but people are still using that. >>> >>> Historically one of the use of underlying block device was cryptoloop, but here >>> I think it should be completely deprecated (cryptsetup can handle all old loop >>> modes as well and default modes for cryptoloop are not safe). >>> [Can we finally remove crypto loop option it from kernel? ... ok, just tried:)] >>> >>> There is also out of tree loop-aes based on heavily patched loop device >>> which usually uses block device underneath >>> (cryptsetup already can handle all loop-aes modes as well). >>> >>> Sometimes it is used with --offset parameter for some reason >>> (like linear device-mapper mapping). >>> >>> So I do not care if you do not support discard here but please do not break >>> support for block device mapped through loop. >> >> I do not think that this is the case with my patch. Also, as you know using >> discard on encrypted device is not a good idea. > > It's not a bizarre use case at all, so would be nice to support like we > support anything else over a bdev as well. Your patch should not break > it, so looks fine. C'mon... it's bizarre! Loopback mounting a block device, to make it look like a block device? Anyway... > Shall we queue it up for 3.2? It's a good way to beat on fs discard > support, fio could be easily configured for that. Fine by me. Reviewed-by: Jeff Moyer <jmoyer@xxxxxxxxxx> -- 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
