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. 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. -- 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
