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    SubjectRe: [PATCH 5/5] ext4: Fix endian problem in MMP initialization
    Date
    You can add my

    Acked-by: Andreas Dilger <adilger@dilger.ca>

    to this.

    Cheers, Andreas

    On 2011-10-21, at 3:18 PM, "Darrick J. Wong" <djwong@us.ibm.com> wrote:

    > As part of startup, the MMP initialization code does this:
    >
    > mmp->mmp_seq = seq = cpu_to_le32(mmp_new_seq());
    >
    > Next, mmp->mmp_seq is written out to disk, a delay happens, and then the MMP
    > block is read back in and the sequence value is tested:
    >
    > if (seq != le32_to_cpu(mmp->mmp_seq)) {
    > /* fail the mount */
    >
    > On a LE system such as x86, the *le32* functions do nothing and this works.
    > Unfortunately, on a BE system such as ppc64, this comparison becomes:
    >
    > if (cpu_to_le32(new_seq) != le32_to_cpu(cpu_to_le32(new_seq)) {
    > /* fail the mount */
    >
    > Except for a few palindromic sequence numbers, this test always causes the
    > mount to fail, which makes MMP filesystems generally unmountable on ppc64. The
    > attached patch fixes this situation.
    >
    > Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
    > ---
    > fs/ext4/mmp.c | 3 ++-
    > 1 files changed, 2 insertions(+), 1 deletions(-)
    >
    >
    > diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c
    > index 9bdef3f..a7a4986 100644
    > --- a/fs/ext4/mmp.c
    > +++ b/fs/ext4/mmp.c
    > @@ -295,7 +295,8 @@ skip:
    > /*
    > * write a new random sequence number.
    > */
    > - mmp->mmp_seq = seq = cpu_to_le32(mmp_new_seq());
    > + seq = mmp_new_seq();
    > + mmp->mmp_seq = cpu_to_le32(seq);
    >
    > retval = write_mmp_block(bh);
    > if (retval)
    >
    > --
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