linux-kernel - Re: [PATCH] HID: uhid: actually use the err number from userspace

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Message-ID: <CADyDSO4x49GWdRVkW=cytvMc7rM3NJkJ4-Sj-FjM9Gday7C-iw@mail.gmail.com>
Date:   Tue, 13 Aug 2019 12:49:57 +0200
From:   David Rheinsberg <david.rheinsberg@...il.com>
To:     Benjamin Tissoires <benjamin.tissoires@...hat.com>
Cc:     Jiri Kosina <jikos@...nel.org>, linux-input@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] HID: uhid: actually use the err number from userspace

Hey

On Mon, Aug 12, 2019 at 6:21 PM Benjamin Tissoires
<benjamin.tissoires@...hat.com> wrote:
>
> This can help debugging the situation
>
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
> ---
>
> Hi,
>
> not entirely sure if we can use this in a such simple way.
>
> However, this is useful to mimic device behaviour from userspace.
>
> Cheers,
> Benjamin
>
>  drivers/hid/uhid.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c
> index fa0cc0899827..2fa32e7fc733 100644
> --- a/drivers/hid/uhid.c
> +++ b/drivers/hid/uhid.c
> @@ -284,7 +284,7 @@ static int uhid_hid_set_report(struct hid_device *hid, unsigned char rnum,
>                 goto unlock;
>
>         if (uhid->report_buf.u.set_report_reply.err)
> -               ret = -EIO;
> +               ret = -uhid->report_buf.u.set_report_reply.err;

I am generally in favor of this. But:

1) can you do this for both set_report *and* get_report?

2) I think you have to filter some of the error codes. For instance,
if you return one of the -ERESTARTSYS codes, this might cause the
syscall to restart (if auto-restart is enabled on this context). At
the same time, this is not *that* bad. It might even be useful for the
userspace driver to trigger an EINTR. At least we should be aware of
this. So maybe filters are not necessary.. Mhhh. Comments?

Thanks
David

>         else
>                 ret = count;
>
> --
> 2.19.2
>