On Tue, Oct 11 2016 at 11:44am -0400,
Heinz Mauelshagen <heinzm@xxxxxxxxxx> wrote:
>
>
> On 10/11/2016 05:38 PM, Andy Whitcroft wrote:
> >On Tue, Oct 11, 2016 at 05:04:34PM +0200, Heinz Mauelshagen wrote:
> >>Andy,
> >>
> >>good catch.
> >>
> >>We should rather check for V190 support only in case any
> >>compat feature flags are actually set.
> >>
> >>{
> >>+ if (le32_to_cpu(sb->compat_features) &&
> >>+ le32_to_cpu(sb->compat_features) != FEATURE_FLAG_SUPPORTS_V190)
> >>{
> >> rs->ti->error = "Unable to assemble array: Unknown flag(s)
> >>in compatible feature flags";
> >> return -EINVAL;
> >> }
> >If the feature flags are single bit combinations then I believe the
> >below does check exactly that. Checking for no 1s outside of the
> >expected features, caring not for the value of the valid bits:
> >
> >+ if (le32_to_cpu(sb->compat_features) & ~(FEATURE_FLAG_SUPPORTS_V190)) {
> >
> >with the possibilty to or in additional feature bits as they are added.
>
> Thanks,
> I prefer this to be easier readable.
Readable or not, the code with the != is _not_ future-proof. Whereas
Andy's solution is. If/when a new compat feature comes along then
FEATURE_FLAG_SUPPORTS_V190 would be replaced to be a macro that ORs all
the new compat features together (e.g. FEATURE_FLAG_COMPAT). E.g. how
dm-thin-metadata.c:__check_incompat_features() does.
We can go with the != code for now, since any future changes would
likely cause this test to be changed. Or we could fix it now _for
real_.
Mike
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