Re: Potential static analysis ideas

[Julia Lawall <julia.lawall@inria.fr>]

> > > Also, over 230 files contain functions that return both NULL and ERR_PTR.
> > > A random example, chosen for conciseness, is the following from
> > > fs/overlayfs/inode.c:
> > >
> > > struct inode *ovl_lookup_inode(struct super_block *sb, struct dentry *real,
> > >                                 bool is_upper)
> > > {
> > >       struct inode *inode, *key = d_inode(real);
> > >
> > >          inode = ilookup5(sb, (unsigned long) key, ovl_inode_test, key);
> > >       if (!inode)
> > >                  return NULL;
> > >
> > >          if (!ovl_verify_inode(inode, is_upper ? NULL : real,
> > >                                is_upper ? real : NULL, false)) {
> > >                  iput(inode);
> > >                  return ERR_PTR(-ESTALE);
> > >          }
> > >
> > >          return inode;
> > > }
> > >
> > And that I would consider a coding error.
> > If a function is able to return an error pointer it should _always_
> > return an error pointer; here it would be trivial to return -ENXIO
> > instead of NULL in the first condition.
> >
> > Not doing so is just sloppy programming IMO.
>
> In this case I agree.

I looked at the calling context, and it is not so obvious.  There are
different behaviors in the two cases at both callsites.  It is like what
Dan describes.  If the thing is not available, we just move on.  If it is
available some action is needed.  If there is an actual error, some error
handling is needed.

julia

>
> For optional resources, the ability to return NULL (and for the caller
> not having to care if the check should be for -ENOENT, -ENODEV,
> or something else), and accept NULL for further operations greatly
> simplifies the handling of optional resources like clocks, enable
> gpios, resets, regulators, ...
>
> Gr{oetje,eeting}s,
>
>                         Geert
>
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
>
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds
>
>