On Thu, Apr 09, 2015 at 10:23:08AM +0100, David Howells wrote: > NeilBrown <neilb@xxxxxxx> wrote: > > > Is there a better way? Could a better way be created? Maybe > > SEEK_DATA_RELIABLE ?? > > fiemap() maybe? fiemap is not reliable for mapping holes - it returns extent info, not whether there is data in a range. i.e. there can be data over a hole (e.g. delayed allocation) and fiemap will return it as a hole. cp made this mistake back when fiemap was first introduced, resulting in corrupt file copies. SEEK_HOLE/SEEK_DATA is what you want, as they are page cache coherent, not extent based operations. And, really if you need it to really be able to find real holes, then a superblock flag might be a better way of marking filesystems with the required capability. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
