Re: [PATCH 034/119] xfs: teach rmapbt to support interval queries

Brian Foster
2016-07-09T13:26:03Z

On Fri, Jul 08, 2016 at 05:16:35PM -0700, Darrick J. Wong wrote:
> On Fri, Jul 08, 2016 at 02:34:03PM -0400, Brian Foster wrote:
> > On Thu, Jun 16, 2016 at 06:21:30PM -0700, Darrick J. Wong wrote:
> > > Now that the generic btree code supports querying all records within a
> > > range of keys, use that functionality to allow us to ask for all the
> > > extents mapped to a range of physical blocks.
> > >
> > > v2: Move unwritten bit to rm_offset.
> > >
> > > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > > ---
> > > fs/xfs/libxfs/xfs_rmap.c | 43 ++++++++++++++++++++++++++++++++++++++++
> > > fs/xfs/libxfs/xfs_rmap_btree.h | 9 ++++++++
> > > 2 files changed, 52 insertions(+)
> > >
> > >
> > > diff --git a/fs/xfs/libxfs/xfs_rmap.c b/fs/xfs/libxfs/xfs_rmap.c
> > > index c6a5a0b..0e1721a 100644
> > > --- a/fs/xfs/libxfs/xfs_rmap.c
> > > +++ b/fs/xfs/libxfs/xfs_rmap.c
> > > @@ -184,3 +184,46 @@ out_error:
> > > trace_xfs_rmap_alloc_extent_error(mp, agno, bno, len, false, oinfo);
> > > return error;
> > > }
> > > +
> > > +struct xfs_rmapbt_query_range_info {
> > > + xfs_rmapbt_query_range_fn fn;
> > > + void *priv;
> > > +};
> > > +
> > > +/* Format btree record and pass to our callback. */
> > > +STATIC int
> > > +xfs_rmapbt_query_range_helper(
> > > + struct xfs_btree_cur *cur,
> > > + union xfs_btree_rec *rec,
> > > + void *priv)
> > > +{
> > > + struct xfs_rmapbt_query_range_info *query = priv;
> > > + struct xfs_rmap_irec irec;
> > > + int error;
> > > +
> > > + error = xfs_rmapbt_btrec_to_irec(rec, &irec);
> > > + if (error)
> > > + return error;
> > > + return query->fn(cur, &irec, query->priv);
> > > +}
> > > +
> > > +/* Find all rmaps between two keys. */
> > > +int
> > > +xfs_rmapbt_query_range(
> > > + struct xfs_btree_cur *cur,
> > > + struct xfs_rmap_irec *low_rec,
> > > + struct xfs_rmap_irec *high_rec,
> > > + xfs_rmapbt_query_range_fn fn,
> > > + void *priv)
> > > +{
> > > + union xfs_btree_irec low_brec;
> > > + union xfs_btree_irec high_brec;
> > > + struct xfs_rmapbt_query_range_info query;
> > > +
> > > + low_brec.r = *low_rec;
> > > + high_brec.r = *high_rec;
> >
> > Some checks or asserts that these are actually in order couldn't hurt.
> > Otherwise looks good:
>
> Ok. If low_rec > high_rec then you'll get no results. I'm not sure
> if that's ok or if we should explicitly return -EINVAL for that case?
>

IMO, it's more robust to short circuit this case one way or another
rather than rely on the search implementation, but I'm happy as long as
there's at least an assert. I have no strong preference really as to
whether it returns an error or 0 and an empty set. If that is truly an
unexpected usage, perhaps it's best to just return an error?

Brian

> --D
>
> >
> > Reviewed-by: Brian Foster <bfoster@redhat.com>
> >
> > > + query.priv = priv;
> > > + query.fn = fn;
> > > + return xfs_btree_query_range(cur, &low_brec, &high_brec,
> > > + xfs_rmapbt_query_range_helper, &query);
> > > +}
> > > diff --git a/fs/xfs/libxfs/xfs_rmap_btree.h b/fs/xfs/libxfs/xfs_rmap_btree.h
> > > index 796071c..e926c6e 100644
> > > --- a/fs/xfs/libxfs/xfs_rmap_btree.h
> > > +++ b/fs/xfs/libxfs/xfs_rmap_btree.h
> > > @@ -74,4 +74,13 @@ int xfs_rmap_free(struct xfs_trans *tp, struct xfs_buf *agbp,
> > > xfs_agnumber_t agno, xfs_agblock_t bno, xfs_extlen_t len,
> > > struct xfs_owner_info *oinfo);
> > >
> > > +typedef int (*xfs_rmapbt_query_range_fn)(
> > > + struct xfs_btree_cur *cur,
> > > + struct xfs_rmap_irec *rec,
> > > + void *priv);
> > > +
> > > +int xfs_rmapbt_query_range(struct xfs_btree_cur *cur,
> > > + struct xfs_rmap_irec *low_rec, struct xfs_rmap_irec *high_rec,
> > > + xfs_rmapbt_query_range_fn fn, void *priv);
> > > +
> > > #endif /* __XFS_RMAP_BTREE_H__ */
> > >
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