Dear Duncan, Gmail seems to have mangled the draft of my reply :-/ It's at the bottom.
On 06/02/16 12:57 AM, Duncan wrote: Most of the rest of the userspace tools, in particular, btrfs scrub, subvolume, balance, device, filesystem, send, receive, etc, work by making kernel calls to do the actual work in any case, and they will use the old calls if they need to. The compatibility discussion, meanwhile, is on making mkfs.btrfs (and btrfs-convert) check the running kernel and taking its defaults from what that kernel supports, instead of choosing arbitrary defaults that may be better when supported, but that older kernels don't actually support. Of course there will still be options to set these as desired regardless of defaults, just as there are now, so people using for instance booted to an old recovery kernel for system maintenance can still choose whatever options that version of mkfs.btrfs supports if they know they'll actually be mounting with a newer kernel, but the idea is simply to have mkfs.btrfs act more sanely /by/ /default/ when run on old kernels, so those same old kernels can actually mount a filesystem created with defaults. Along that line, as a distro maintainer of the btrfs-progs package, you may wish to patch the mkfs.btrfs defaults to what your kernel supports. Btrfs-progs will probably ship with kernel-sensitive defaults some time in the future (userspace 4.5 release, probably), but it doesn't do so yet... -- Thank you very much for taking the time to write such a thorough reply. I'm not the maintainer of Debian's btrfs-progs package, but I am investigating the issues preventing the addition of btrfs-progs-4.4 to the backports repository. [ edit: sorry it took me so long to reply, I've been swamped with work. In the meantime, it seems v4.4 has made it into the backports without warnings or compatibility checks, so I want to get my facts straight asap and patch the package with some kind of a notice/alert asap, if only through the debian/NEWS...since there isn't currently a way to depend on a particular kernel series, or ever a kernel version <= 4.4.0 Cheers, Nicholas -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
