On Sep 07, 2009 16:26 +0000, Florian Weimer wrote: > * Andreas Dilger: > > If you are implementing a tool to use this, I would code it to try > > FIEMAP first, then FIBMAP (if it is running as root, or it gets > > fixed in some future kernel), then just do without (as it most likely > > does already today). > > If FIBMAP is unsafe, it's likely exposed by concurrent changes to the > file, so using it would still be unsafe for backup purposes. And I > really only need the number of the first block. (I want to optimize > reading of Maildir-style folders, mainly for backup purposes.) Given that the worst that can happen for your particular application if FIBMAP gets the wrong block number is a sub-optimal ordering for the file copy, there is no risk in doing this. For the FIEMAP code, since you only need the first block number, just pass it a single fiemap_extent so that it doesn't spend time generating a full list of extents that you don't need to use. Cheers, Andreas -- Andreas Dilger Sr. Staff Engineer, Lustre Group Sun Microsystems of Canada, Inc. -- 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
