Linux Virtualization - Aug 2016 - [PATCH] CodingStyle: add some more error handling guidelines

"Michael S. Tsirkin" <mst at redhat.com> writes:
>                 foo = kmalloc(SIZE, GFP_KERNEL);
>                 if (!foo)
>                         goto err_foo;
>
>                 foo->bar = kmalloc(SIZE, GFP_KERNEL);
>                 if (!foo->bar)
>                         goto err_bar;
>                 ...
>
>                 kfree(foo->bar);
>         err_bar:
>
>                 kfree(foo);
>         err_foo:
>
>                 return ret;

I believe the CodingStyle already contain far too much personal style to
be useful as real style guide.  FWIW, I prefer a single error label, at
the "cost" of additional tests in the error path:


                 foo = kmalloc(SIZE, GFP_KERNEL);
                 if (!foo)
                         goto err;
                 foo->bar = kmalloc(SIZE, GFP_KERNEL);
                 if (!foo->bar)
                         goto err;
                 ...
 		 if (ret)
			goto err;
                 return 0;
      err:
                 if (foo)
                        kfree(foo->bar);
                 kfree(foo);
                 return ret;


The advantage is that I don't have to manage X different labels,
ensuring that they have the order is correct if some part of the
function is refactored etc.  That tends to get too complicated for my
simple brain. And since the error path is rarely tested, complicated
equals buggy.

My sample will of course trigger all those nice "optimizing the error
path" patches, but I ignore those anyway so that's not a big deal.


Bj?rn

Dan Carpenter <dan.carpenter at oracle.com> writes:
> Hike up the mountain, then if you get stuck hike back down using the
> exact same path.
OK, I understand what you say.  I just can't resist objecting to that
example ;)

In my experience, finding the exact same path back after hiking up a
mountain is really hard. Especially if you are in enough trouble already
to get stuck. Up and down tend to look completely different.  Looking
back all the time while you go up might help, but finding your way back
by simply taking the reverse path is definitely not easy.


Bj?rn