On Fri, Jul 15, 2016 at 04:21:31PM -0700, Eric Wheeler wrote: > We do btrfs subvolume snapshots over time for backups. I would like to > traverse the files in the subvolumes and find the total unique chunk count > to calculate total space for a set of subvolumes. > > This sounds kind of like the beginning of what a deduplicator would do, > but I just want to count the blocks, so no submission for deduplication. > I started looking at bedup and other deduplicator code, but the answer to > this question wasn't obvious (to me, anyway). > > Questions: > > Is there an ioctl (or some other way) to get the block device offset for a > file (or file offset) so I can count the unique occurances? Yes, FIEMAP. You can play with it via "/usr/sbin/filefrag -v". That /usr/sbin is misleading -- FIEMAP doesn't require root, although its predecessor did need that, https://bugs.debian.org/819923 > What API documentation should I review? In kernel sources, Documentation/filesystems/fiemap.txt Meow! -- An imaginary friend squared is a real enemy. -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
