Tao Ma wrote: > In xfs_vn_fiemap, we set bvm_count to fi_extent_max + 1 and want > to return fi_extent_max extents, but actually it won't work for > a sparse file. The reason is that in xfs_getbmap we will > calculate holes and set it in 'out', while out is malloced by > bmv_count(fi_extent_max+1) which didn't consider holes. So in the > worst case, if 'out' vector looks like > [hole, extent, hole, extent, hole, ... hole, extent, hole], > we will only return half of fi_extent_max extents. > > So in xfs_vn_fiemap, we should consider this worst case. If the > user wants fi_extent_max extents, we need a 'out' with size of > 2 *fi_extent_max + 1. This all seems right to me, though your commit message above (+1) doesn't match the comment and code in the patch (+2) -Eric > Cc: Alex Elder <aelder@xxxxxxx> > Cc: Christoph Hellwig <hch@xxxxxx> > Cc: Dave Chinner <david@xxxxxxxxxxxxx> > Signed-off-by: Tao Ma <tao.ma@xxxxxxxxxx> > --- > fs/xfs/linux-2.6/xfs_iops.c | 16 ++++++++++++++-- > 1 files changed, 14 insertions(+), 2 deletions(-) > > diff --git a/fs/xfs/linux-2.6/xfs_iops.c b/fs/xfs/linux-2.6/xfs_iops.c > index 9c8019c..1db92e3 100644 > --- a/fs/xfs/linux-2.6/xfs_iops.c > +++ b/fs/xfs/linux-2.6/xfs_iops.c > @@ -672,9 +672,21 @@ xfs_vn_fiemap( > else > bm.bmv_length = BTOBB(length); > > - /* We add one because in getbmap world count includes the header */ > + /* > + * It is a bit tricky for us to calculate the bmv_count from > + * fi_extent_max. > + * If we support to return fi_extent_max extents to the user, > + * we need at most 2 * fi_extent_max + 1 for bmv_count since > + * in xfs_getbmap we will calculate holes while fi_extent_max > + * don't have them. So in the worst case, bmv can looks like > + * [hole, extent, hole, extent, hole, ... hole, extent, hole]. > + * So there will be 2 *fi_extent_max + 1. > + * What's more, in getbmap world count have to include the > + * header, so we need another bmv. So the total number will > + * be 2 * fieinfo->fi_extents_max + 2. > + */ > bm.bmv_count = !fieinfo->fi_extents_max ? MAXEXTNUM : > - fieinfo->fi_extents_max + 1; > + 2 * fieinfo->fi_extents_max + 2; > bm.bmv_count = min_t(__s32, bm.bmv_count, > (PAGE_SIZE * 16 / sizeof(struct getbmapx))); > bm.bmv_iflags = BMV_IF_PREALLOC; _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
