On Mon, Jun 14, 2010 at 10:27:06AM +1000, Dave Chinner wrote: > On Sat, Jun 12, 2010 at 10:08:15AM +0800, Tao Ma wrote: > > 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. > > Right, it's not broken, we simply return less than fi_extent_mex > extents when there are holes. I don't see that as a problem as > applications have to handle that case anyway, and.... > > > 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 + 2(one more the header). > > That's rather dangerous, I think. It relies on other code to catch > the buffer overrun that this sets up for fragmented, non-sparse > files. Personally I'd much prefer to return fewer extents for sparse > files than to add a landmine like this into the kernel code.... I just had a thought - if you want to avoid holes being reported to fiemap, then add a BMV_IF_NO_HOLES flag to xfs_getbmap() and skip holes in the mappin gloop when this flag is set. That will make fiemap fill in the full number of extents without hacking the extent count... Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
