Re: [PATCH 4/4] vgaswitcheroo: do not check for NULL debugfs dentry

[Lukas Wunner <lukas@wunner.de>]

On Mon, Oct 11, 2021 at 10:24:29PM +0200, Lukas Wunner wrote:
> On Mon, Oct 11, 2021 at 09:06:07PM +0200, Nirmoy Das wrote:
> > Debugfs APIs returns encoded error on failure so use
> > debugfs_lookup() instead of checking for NULL.
> [...]
> > --- a/drivers/gpu/vga/vga_switcheroo.c
> > +++ b/drivers/gpu/vga/vga_switcheroo.c
> > @@ -914,7 +914,7 @@ static void vga_switcheroo_debugfs_fini(struct vgasr_priv *priv)
> >  static void vga_switcheroo_debugfs_init(struct vgasr_priv *priv)
> >  {
> >  	/* already initialised */
> > -	if (priv->debugfs_root)
> > +	if (debugfs_lookup("vgaswitcheroo", NULL))
> >  		return;
> > 
> >  	priv->debugfs_root = debugfs_create_dir("vgaswitcheroo", NULL);
> 
> If debugfs_create_dir() returns an error code, it does make sense to
> retry the call when another vga_switcheroo client registers later.
> I like that.
> 
> However I'd prefer simply changing this to explicitly check for NULL, i.e.:
> 
> -	if (priv->debugfs_root)
> +	if (priv->debugfs_root == NULL)

Apologies, I meant:

-	if (priv->debugfs_root)
+	if (priv->debugfs_root && !IS_ERR(priv->debugfs_root))

Thanks,

Lukas

> It's just as clear as calling debugfs_lookup() and it has way less
> overhead.  Granted, this isn't a hot path, but it's called on boot,
> and the less code we execute, the faster the machine boots.