On 2010-10-06 16:35, Fred Isaman wrote:
> Right now, when we set the stateid, we blindly overwrite the current
> one, allowing the seqid to incorrectly roll backward.
>
> Signed-off-by: Fred Isaman <iisaman@xxxxxxxxxx>
> ---
> fs/nfs/pnfs.c | 38 ++++++++++++++++++++++++++++++++------
> 1 files changed, 32 insertions(+), 6 deletions(-)
>
> diff --git a/fs/nfs/pnfs.c b/fs/nfs/pnfs.c
> index 39bce9b..555955b 100644
> --- a/fs/nfs/pnfs.c
> +++ b/fs/nfs/pnfs.c
> @@ -459,16 +459,42 @@ pnfs_destroy_all_layouts(struct nfs_client *clp)
> }
> }
>
> +/* update lo->stateid with new if is more recent
> + *
> + * lo->stateid could be the open stateid, in which case we just use what given.
> + */
> static void
> pnfs_set_layout_stateid(struct pnfs_layout_hdr *lo,
> - const nfs4_stateid *stateid)
> + const nfs4_stateid *new)
> {
> - /* TODO - should enforce that embedded seqid, in the case
> - * that the two stateid.others are equal, only increases.
> - * Complicated by wrap-around.
> - */
> + nfs4_stateid *old = &lo->stateid;
> + bool overwrite = false;
> +
> write_seqlock(&lo->seqlock);
> - memcpy(lo->stateid.data, stateid->data, sizeof(lo->stateid.data));
> + if (!test_bit(NFS_LAYOUT_STATEID_SET, &lo->state) ||
> + memcmp(old->stateid.other, new->stateid.other, sizeof(new->stateid.other)))
> + overwrite = true;
> + else {
> + u32 oldseq, newseq, limit;
> +
> + oldseq = be32_to_cpu(old->stateid.seqid);
> + newseq = be32_to_cpu(new->stateid.seqid);
> + /* There are no good bounds on window size, so just
> + * use a ridiculously large window of 2^31.
> + */
> + limit = oldseq + (1 << 31);
> + if (oldseq < limit) {
> + /* The easy, non-wraparound case */
> + if (oldseq < newseq && newseq < limit)
> + overwrite = true;
> + } else {
> + /* Near wraparound edge */
> + if (oldseq < newseq || newseq < limit)
> + overwrite = true;
> + }
Wouldn't it be simpler to just look at (int32_t)(newseq - oldseq)?
Benny
> + }
> + if (overwrite)
> + memcpy(&old->stateid, &new->stateid, sizeof(new->stateid));
> write_sequnlock(&lo->seqlock);
> }
>
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