[lvm-devel] dm: introduce DM_GET_TARGET_VERSION
Mike Snitzer
snitzer at redhat.com
Tue Sep 17 13:39:03 UTC 2019
On Tue, Sep 17 2019 at 2:32am -0400,
Christoph Hellwig <hch at infradead.org> wrote:
> On Mon, Sep 16, 2019 at 08:16:41PM +0200, Milan Broz wrote:
> >
> > So the main idea behind this was just use already existing functionality
> > in kernel DM, and provide simple user-friendly way to detect some incompatibilites
> > more early. If detection is not there, we just fallback to the old way.
>
> Well, and the nice way to do that is to actually report the features,
> not some arbitrary version number. That is have a sysfs file (or
> ioctl for dm if that is the way to go) that reports a list of
> capabilities. Then userspace checks for that desired capability and
> only tries the feture if it is supported.
A target's version, while opaque and imperfect, has served DM pretty
well for a long time. Requires discipline when backporting changes but
stable@ version bumps generally don't occur because such a bump triggers
conflicts across the N stable@ kernels.
So I'm not opposed to fined grained reporting of target features. But
doing so can come later.
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