From mboxrd@z Thu Jan  1 00:00:00 1970
From: Greg KH <gregkh@linuxfoundation.org>
Subject: Re: [PATCH v2 6/6] misc: fastrpc: Add support for compat ioctls
Date: Wed, 12 Dec 2018 12:50:37 +0100
Message-ID: <20181212115037.GA31075@kroah.com>
References: <20181207163513.16412-1-srinivas.kandagatla@linaro.org>
 <20181207163513.16412-7-srinivas.kandagatla@linaro.org>
 <20181212105932.GA1990@kroah.com>
 <864aaef3-8d60-3beb-ce20-a9f41f78a32f@linaro.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Return-path: <linux-kernel-owner@vger.kernel.org>
Content-Disposition: inline
In-Reply-To: <864aaef3-8d60-3beb-ce20-a9f41f78a32f@linaro.org>
Sender: linux-kernel-owner@vger.kernel.org
To: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Cc: robh+dt@kernel.org, arnd@arndb.de, mark.rutland@arm.com, devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, bjorn.andersson@linaro.org, linux-arm-msm@vger.kernel.org, bkumar@qti.qualcomm.com, thierry.escande@linaro.org
List-Id: devicetree@vger.kernel.org

On Wed, Dec 12, 2018 at 11:44:05AM +0000, Srinivas Kandagatla wrote:
> Thanks for the comments,
> 
> On 12/12/18 10:59, Greg KH wrote:
> > > This patch adds support for compat ioctl from 32 bits userland to
> > > Qualcomm fastrpc driver.
> > Ick, why?
> > 
> > Why not just fix up your ioctl structures to not need that at all?  For
> > new code being added to the kernel, there's no excuse to have to have
> > compat structures anymore, just make your api sane and all should be
> > fine.
> 
> Yes, I did try that after comments from Arnd,
> 
> 
> > 
> > What prevents you from doing that and requiring compat support?
> > 
> I removed most of the compat IOCTLS except this one.
> The reason is that this ioctl takes arguments which can vary in number for
> each call.

Then do not do that :)

Remember, you get to design the api, fix the structure size to work
properly everywhere.

> So args are passed as pointer to structure, rather than fixed
> size. I could not find better way to rearrange this to give a fixed size
> data structure. In theory number of arguments can vary from 0-255 for both
> in & out.
> 
> current data structure looks like this:
> 
> struct fastrpc_invoke_args {
> 	__s32 fd;
> 	size_t length;
> 	void *ptr;
> };

Make length and ptr both __u64 and you should be fine, right?  If you do
that, might as well make fd __u64 as well to align things better.

> struct fastrpc_invoke {
> 	__u32 handle;
> 	__u32 sc;
> 	struct fastrpc_invoke_args *args;
> };
> 
> Other option is to split this IOCTL into 3 parts
> SET_INVOKE_METHOD, SET_INVOKE_ARGS and INVOKE
> with some kinda handle to bind these three.
> 
> with below structures:
> struct fastrpc_invoke {
> 	__u32 handle;
> 	__u32 sc;
> };
> 
> struct fastrpc_invoke_arg {
> 	__s32 fd;
> 	__u64 length;
> 	__u64 ptr;
> };
> I can try this and see how this works before I send next version of patch!

No need to have 3 calls, just change your one structure and you should
be fine.

thanks,

greg k-h