[libvirt] [PATCH] util: mdev: Treat the 'name' sysfs attribute as optional

[Erik Skultety]

On Tue, Mar 06, 2018 at 11:47:51AM -0500, John Ferlan wrote:
>
>
> On 03/05/2018 09:43 AM, Erik Skultety wrote:
> > When commit 3545cbef moved the sysfs attribute reading logic from
> > _udev.c module to virmdev.c, it had to replace our udev read wrappers
> > with the ones available from virfile.c. The problem is that the original
> > logic worked correctly with udev read wrappers which don't return an
> > error code for a missing attribute, virfile.c readers however - not so
> > much. Therefore add another parameter to the macro, so we can again
> > accept the fact that optional attributes may be missing.
> >
> > Signed-off-by: Erik Skultety <eskultet at redhat.com>
> > ---
> >  src/util/virmdev.c | 17 +++++++++++------
> >  1 file changed, 11 insertions(+), 6 deletions(-)
> >
>
> The virFileReadValue* API's return -2 for non existing file, so instead
> of messing with errno, you should be able to
>
>     rc = cb();
>     if (rc == -2 && optional)
>         rc = 0;
>     if (rc < 0)
>         goto cleanup;
>
> As it seems to be the more common way to use the functions.

Honestly, that was my first approach, but then I told myself that rather than
comparing against a "magic" value which in order to understand the caller has
to go and read the function being called, so I went for the errno and I liked it
more, it's standardized (you don't care what the function does and under what
circumstances it returns, you just want the errno), there was less lines of code
involved, I can change it if you insist, but I wanted to express my intentions
first.

Erik