On 03/08/16 21:37, Adam Borowski wrote: > On Wed, Aug 03, 2016 at 08:56:01PM +0100, Graham Cobb wrote: >> Are there any btrfs commands (or APIs) to allow a script to create a >> list of all the extents referred to within a particular (mounted) >> subvolume? And is it a reasonably efficient process (i.e. doesn't >> involve backrefs and, preferably, doesn't involve following directory >> trees)? > > Since the size of your output is linear to the number of extents which is > between the number of files and sum of their sizes, I see no gain in > trying to avoid following the directory tree. Thanks for the help, Adam. There are a lot of files and a lot of directories - find, "ls -R" and similar operations take a very long time. I was hoping that I could query some sort of extent tree for the subvolume and get the answer back in seconds instead of multiple minutes. But I can follow the directory tree if I need to. >> I am not looking to relate the extents to files/inodes/paths. My >> particular need, at the moment, is to work out how much of two snapshots >> is shared data, but I can think of other uses for the information. > > Thus, unlike the question you asked above, you're not interested in _all_ > extents, merely those which changed. > > You may want to look at "btrfs subv find-new" and "btrfs send --no-data". Unfortunately, the subvolumes do not have an ancestor-descendent relationship (although they do have some common ancestors), so I don't think find-new is much help (as far as I can see). But just looking at the size of the output from "send -c" would work well enough for the particular problem I am trying to solve tonight! Although I will need to take read-only snapshots of the subvolumes to allow send to work. Thanks for the suggestion. I would still be interested in the extent list, though. The main problem with find-new and send is that they don't tell me how much has been deleted, only added. I am thinking about using the extents to get a much better handle on what is using up space and what I could recover if I removed (or moved to another volume) various groups of related subvolumes. Thanks again for the help. -- 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
