lkml.org 
[lkml]   [2004]   [Feb]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: dm-crypt using kthread
    Grzegorz Kulewski wrote:
    > Could somebody write dm-compress (compressing not encrypting)? Is it
    > technically possible (can device mapper handle different data size at
    > input, differet at output)? (I think there is compressing loop patch.)
    > Could dm first compress data (even with weak algorithm), then encrypt, to
    > make statistical analysis harder?


    It's certainly possible, but you have to consider that data transfer
    almost always should be considered in page-sized chunks. For compress
    that would imply you would need to allocate/free blocks and similar
    duties that a filesystem must perform, simply because you do not have
    one-to-one correspondence with blocks being passed to you.

    You also have to consider that the kernel may request one or more pages
    that are in the middle of a compressed run of pages. For example,
    consider an algorithm that compresses 16 pages into a run of 4 pages.
    Later on, when the kernel requests (uncompressed) page 9, you likely
    need to read all 4 pages, and allocate 16 more pages for decompression.
    So, reading 1 upper layer page required dm-compress tying up 20 pages.

    Jeff



    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2005-03-22 14:00    [W:0.027 / U:125.088 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site