On 2011-08-18 21:20, Lukas Czerner wrote: > 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! Alright, lets do that. > Btw I am not sure what do you mean by "beat on fs discard support" :). Perhaps worded a bit weird, what I mean was "thoroughly exercise and test file system discard support" :-) -- 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
