[libvirt] [PATCH] util: Fix configure.ac check for DEVLINK_CMD_ESWITCH_GET

[Andrea Bolognani]

On Tue, 2017-09-19 at 07:27 -0400, John Ferlan wrote:
> > First of all, you're removing a number of checks
> > on unrelated symbols
> > that are still used in the code, and if any of those is not present
> > then we shouldn't compile the relevant bits at all.
> 
> I checked - up through 4.8 "most" are available. At 4.8 the *ESWITCH*
> ones were added. Checking for a minimum version for a symbol is
> something we do in other code under the assumption that any symbol that
> is in a counted enum/list for a command or structure before it is
> available. Otherwise, we'd have more symbol and field checking all over
> the place.

Okay, I see what you were aiminig for now, and I don't disagree
with it; however, the rationale was not explained clearly in the
original commit message.

> > Second, we're using
> > DEVLINK_CMD_ESWITCH_GET in the code, but as you
> > explain that version is only available in newer kernels.
> > 
> > I think the approach need to be more nuanced:
> > 
> >   - use
> > DEVLINK_CMD_ESWITCH_GET or DEVLINK_CMD_ESWITCH_MODE_GET,
> >     depending on which on is available, with the former one being the
> >     preferred option;
> 
> That's another option to what I posted a few moments ago to use:
> 
> # ifndef...

Sure, that would work too, and look a little bit better than
what I proposed.

-- 
Andrea Bolognani / Red Hat / Virtualization