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    SubjectRe: [PATCH] loop: add discard support for loop devices
    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.

    Thanks!
    -Lukas

    >
    > Thanks,
    > Milan
    >

    --


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