Tao Ma wrote: > Eric Sandeen wrote: >> 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) >> > oh, yes, I will change the commit log and send a v2. > and can I add your ack for this patch? Sure, it seems right to me. Thanks, -Eric > Regards, > Tao >> -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; >>> >> >> -- >> To unsubscribe from this list: send the line "unsubscribe >> linux-kernel" in >> the body of a message to majordomo@xxxxxxxxxxxxxxx >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> Please read the FAQ at http://www.tux.org/lkml/ >> > _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
