On Thu, 18 Aug 2011, Jens Axboe wrote: > 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. > That would be great, thanks! Btw I am not sure what do you mean by "beat on fs discard support" :). -Lukas -- 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
