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    SubjectRe: [PATCH 3/6] direct-io: do not merge logically non-contiguous requests
    On Fri, May 21, 2010 at 06:47:36PM -0700, Mike Fedyk wrote:
    > On Fri, May 21, 2010 at 10:03 AM, Josef Bacik <josef@redhat.com> wrote:
    > > Btrfs cannot handle having logically non-contiguous requests submitted.  For
    > > example if you have
    > >
    > > Logical:  [0-4095][HOLE][8192-12287]
    > > Physical: [0-4095]      [4096-8191]
    > >
    > > Normally the DIO code would put these into the same BIO's.  The problem is we
    > > need to know exactly what offset is associated with what BIO so we can do our
    > > checksumming and unlocking properly, so putting them in the same BIO doesn't
    > > work.  So add another check where we submit the current BIO if the physical
    > > blocks are not contigous OR the logical blocks are not contiguous.
    > >
    > > Signed-off-by: Josef Bacik <josef@redhat.com>
    > > ---
    > >
    > > V1->V2
    > > -Be more verbose in the in-code comment
    > >
    > >  fs/direct-io.c |   20 ++++++++++++++++++--
    > >  1 files changed, 18 insertions(+), 2 deletions(-)
    > >
    >
    > Btrfs has been pretty much self-contained (working well compiled
    > against 2.6.32 for example). Is there a way that this wouldn't just
    > start silently breaking for people compiling the latest btrfs with
    > dkms against older kernels?

    Nope, you have to have these generic patches for DIO to work, so building btrfs
    like this will stop working with earlier kernels. Thanks,

    Josef
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