From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A89D41876; Tue, 12 Apr 2022 04:56:15 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D03D7C385A1; Tue, 12 Apr 2022 04:56:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1649739375; bh=m6VSt+/v92P1Zg4jzcDGMViyz4qsqAMT7JU7EYUuzrw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=XBsvbAIF0QEh7W6YUXlTe15h0Z8iar99m1/jK+vE1MRBUmrj0RIvjCPobYTf1BFOd s0bgHJKvz5h/MNww7jnZf5XH0Od3r2VIQTtYRWudOz8l7gD1cc8Xw0qEWqUGArCKIl ITWIyqvUQr4j1ChMzkPezdF/PC+SmZdieWIkK5Eg= Date: Tue, 12 Apr 2022 06:56:12 +0200 From: Greg Kroah-Hartman To: Jaehee Park Cc: Johan Hovold , Alex Elder , greybus-dev@lists.linaro.org, linux-staging@lists.linux.dev, linux-kernel@vger.kernel.org, outreachy@lists.linux.dev Subject: Re: [PATCH] staging: greybus: replace zero-element array with flexible-array Message-ID: References: <20220411211411.GA2796005@jaehee-ThinkPad-X1-Extreme> Precedence: bulk X-Mailing-List: linux-staging@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220411211411.GA2796005@jaehee-ThinkPad-X1-Extreme> On Mon, Apr 11, 2022 at 05:14:11PM -0400, Jaehee Park wrote: > Zero-length and one-element arrays are deprecated. Flexible-array > members should be used instead. Flexible-array members are > recommended because this is the way the kernel expects dynamically > sized trailing elements to be declared. > Refer to Documentation/process/deprecated.rst. > > Change the zero-length array, buf, in the struct > gb_usb_hub_control_response to a flexible array. And add wLength as a > member of the struct so that the struct is not a zero-sized struct. > > Issue found by flexible_array coccinelle script. > > Signed-off-by: Jaehee Park > --- > > I have a question for the authors: > I saw a fixme comment in the hub_control function in usb.c: > / FIXME: handle unspecified lengths / > > I was wondering why this comment was left there? > > In this patch, I'm using this struct: > > struct gb_usb_hub_control_response { > __le16 wLength; > u8 buf[]; > }; > > And instead of using response_size, I'm doing this: > > struct gb_usb_hub_control_response *response; > And using sizeof(*response) as the input to gb_operation_create. > > Would the flexible array address the handling of unspecified lengths > issue (in the fixme comment)? No, you can not change the format of the data on the bus without also changing the firmware in the device and usually the specification as well. > drivers/staging/greybus/usb.c | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/drivers/staging/greybus/usb.c b/drivers/staging/greybus/usb.c > index 8e9d9d59a357..d0b2422401df 100644 > --- a/drivers/staging/greybus/usb.c > +++ b/drivers/staging/greybus/usb.c > @@ -27,7 +27,8 @@ struct gb_usb_hub_control_request { > }; > > struct gb_usb_hub_control_response { > - u8 buf[0]; > + __le16 wLength; > + u8 buf[]; What is wrong with buf[0] here? You can fix this in other ways if you really understand the difference between [0] and [] in C. Please look at many of the other conversions if you wish to do this. thanks, greg k-h