11:20 a.m.
On Sat, Apr 18 2020, Alan Stern wrote:
On Sat, 18 Apr 2020, Matthew Wilcox wrote:
> On Sat, Apr 18, 2020 at 11:41:07AM -0700, Randy Dunlap wrote:
> > +++ linux-next-20200327/drivers/usb/core/sysfs.c
> > @@ -1263,7 +1263,7 @@ void usb_create_sysfs_intf_files(struct
> > if (!alt->string && !(udev->quirks &
USB_QUIRK_CONFIG_INTF_STRINGS))
> > alt->string = usb_cache_string(udev, alt->desc.iInterface);
> > if (alt->string && device_create_file(&intf->dev,
&dev_attr_interface))
> > - ; /* We don't actually care if the function fails. */
> > + do_empty(); /* We don't actually care if the function fails. */
> > intf->sysfs_files_created = 1;
> > }
>
> Why not just?
>
> + if (alt->string)
> + device_create_file(&intf->dev, &dev_attr_interface);
This is another __must_check function call.
The reason we don't care if the call fails is because the file
being created holds the USB interface string descriptor, something
which is purely informational and hardly ever gets set (and no doubt
gets used even less often).
Is this another situation where the comment should be expanded and the
code modified to include a useless test and cast-to-void?
Or should device_create_file() not be __must_check after all?
One approach to dealing with __must_check function that you don't want
to check is to cause failure to call
pr_debug("usb: interface descriptor file not created");
or similar. It silences the compiler, serves as documentation, and
creates a message that is almost certainly never seen.
This is what I did in drivers/md/md.c...
if (mddev->kobj.sd &&
sysfs_create_group(&mddev->kobj, &md_bitmap_group))
pr_debug("pointless warning\n");
(I give better warnings elsewhere - I must have run out of patience by
this point).
NeilBrown