Re: [PATCH v2 3/5] btrfs-progs: kernel based default features for mkfs

[Christoph Anton Mitterer <calestyo@scientia.net>]

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On Mon, 2015-11-23 at 11:05 -0500, Austin S Hemmelgarn wrote:
> I would find it useful if btrfs gives a warning if it creates a
> > filesystem which (because unsupported in the current kernel) lacks
> > features which are considered default by then.
> It should give a warning if the user requests a feature that is 
> unsupported by the kernel it's being run on, but it should not by 
> default try to enable something that isn't supported by the kernel
> it's 
> running on.
Well that as well, and of course it shouldn't try to enable a feature
that wouldn't work, but what I meant was, e.g. if I create a fs with
btrfs-progs 4.3 (where skinny-extents are default) but on such an old
kernel where this isn't supported yet,... it should tell me "Normally
I'd create the fs with skinny-extents, but I don't as your kernel is
too old".


> It is actually possible to clone a btrfs filesystem, just not in a
> way 
> that people used to stuff like ext4 would recognize.  In essence, you
> need to take the FS mostly off-line, force all subvolumes to read-
> only, 
> then use send-receive to transfer things, and finally make the 
> subvolumes writable again.  I've been considering doing a script to
> do 
> this automatically, but have never gotten around to it as it's not 
> something that is quick to code, and it's not something I do very
> often.
And that would also keep all ref-links, etc.? I.e. the copied fs
wouldn't eat up much more space than the original?
Well than such script should be part of btrfs-progs :-)

Cheers,
Chris.

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