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Date: Wed, 13 Apr 2022 00:50:31 -0400 From: Jaehee Park <jhpark1013@...il.com> To: Greg Kroah-Hartman <gregkh@...uxfoundation.org> Cc: Johan Hovold <johan@...nel.org>, Alex Elder <elder@...nel.org>, greybus-dev@...ts.linaro.org, linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org, outreachy@...ts.linux.dev Subject: Re: [PATCH] staging: greybus: replace zero-element array with flexible-array On Tue, Apr 12, 2022 at 06:57:11AM +0200, Greg Kroah-Hartman wrote: > On Tue, Apr 12, 2022 at 06:56:12AM +0200, Greg Kroah-Hartman wrote: > > 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 <jhpark1013@...il.com> > > > --- > > > > > > 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. > > And I would not recommend this as an "outreachy introduction task" > unless you understand this. There are much easier first patch tasks you > can accomplish instead. > Hi Greg, I should've made this into a question for the maintainers instead of a patch. Sorry about that. Dan's and your comments are well noted. Thank you, Jaehee > good luck! > > greg k-h
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