Christoph, On Sat, 2 Apr 2011 12:40:11 AM Chris Mason wrote: > Excerpts from Christoph Hellwig's message of 2011-04-01 09:34:05 -0400: > > > I don't think it's a good idea to introduce any user visible > > operations over subvolume boundaries. Currently we don't have > > any operations over mount boundaries, which is pretty > > fumdamental to the unix filesystem semantics. If you want to > > change this please come up with a clear description of the > > semantics and post it to linux-fsdevel for discussion. That of > > course requires a clear description of the btrfs subvolumes, > > which is still completely missing. > > The subvolume is just a directory tree that can be snapshotted, and > has it's own private inode number space. > > reflink across subvolumes is no different from copying a file from > one subvolume to another at the VFS level. The src and > destination are different files and different inodes, they just > happen to share data extents. Were Chris Mason's points above enough to sway your opposition to this functionality/patch? There is demand for the ability to move data between subvolumes without needing to copy the extents themselves, it's cropped up again on the list in recent days. It seems a little hard (and counterintuitive) to enforce a wasteful use of resources to copy data between different parts of the same filesystem which happen to be a on a different subvolume when it's permitted & functional to the same filesystem on the same subvolume. I don't dispute the comment about documentation on subvolumes though, there is a short discussion of them on the btrfs wiki in the sysadmins guide, but not really a lot of detail. :-) All the best, Chris -- Chris Samuel : http://www.csamuel.org/ : Melbourne, VIC This email may come with a PGP signature as a file. Do not panic. For more info see: http://en.wikipedia.org/wiki/OpenPGP
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