linux-kernel - Re: [PATCH v3] firewire: Remove function callback casts

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Message-ID: <20200708130628.GA21753@workstation>
Date:   Wed, 8 Jul 2020 22:06:28 +0900
From:   Takashi Sakamoto <o-takashi@...amocchi.jp>
To:     Oscar Carter <oscar.carter@....com>
Cc:     Kees Cook <keescook@...omium.org>,
        Stefan Richter <stefanr@...6.in-berlin.de>,
        kernel-hardening@...ts.openwall.com,
        linux1394-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] firewire: Remove function callback casts

Hi,

I'm sorry to be late but I was stuck at my work for ALSA control
service programs for audio and music units on IEEE 1394 bus[1].

On Sat, May 30, 2020 at 11:08:39AM +0200, Oscar Carter wrote:
> In 1394 OHCI specification, Isochronous Receive DMA context has several
> modes. One of mode is 'BufferFill' and Linux FireWire stack uses it to
> receive isochronous packets for multiple isochronous channel as
> FW_ISO_CONTEXT_RECEIVE_MULTICHANNEL.
> 
> The mode is not used by in-kernel driver, while it's available for
> userspace. The character device driver in firewire-core includes
> cast of function callback for the mode since the type of callback
> function is different from the other modes. The case is inconvenient
> to effort of Control Flow Integrity builds due to
> -Wcast-function-type warning.
> 
> This commit removes the cast. A static helper function is newly added
> to initialize isochronous context for the mode. The helper function
> arranges isochronous context to assign specific callback function
> after call of existent kernel API. It's noticeable that the number of
> isochronous channel, speed, and the size of header are not required for
> the mode. The helper function is used for the mode by character device
> driver instead of direct call of existent kernel API.
> 
> The same goal can be achieved (in the ioctl_create_iso_context function)
> without this helper function as follows:
> - Call the fw_iso_context_create function passing NULL to the callback
>   parameter.
> - Then setting the context->callback.sc or context->callback.mc
>   variables based on the a->type value.
> 
> However using the helper function created in this patch makes code more
> clear and declarative. This way avoid the call to a function with one
> purpose to achieved another one.
> 
> Co-developed-by: Takashi Sakamoto <o-takashi@...amocchi.jp>
> Signed-off-by: Takashi Sakamoto <o-takashi@...amocchi.jp>
> Co-developed-by: Stefan Richter <stefanr@...6.in-berlin.de>
> Signed-off-by: Stefan Richter <stefanr@...6.in-berlin.de>
> Signed-off-by: Oscar Carter <oscar.carter@....com>
> ---
> Hi,
> 
> this is another proposal to achieved the goal of remove function callback
> cast start by me with the first [1] and second [2] versions, and followed
> by the work of Takashi Sakamoto with his first [3] and second [4] versions,
> and the code of Stefan Richter [5].
> 
> The purpose of this third version is to put together all the work done
> until now following the comments of all reviewed patches.
> 
> I've added the "Co-developed-by" and "Signed-off-by" tags to give credit to
> Takashi Sakamoto and Stefan Richter if there are no objections.
 
In my opinion, it's no need to add my and Stefan's sign-off tag to patch
in which you firstly wrote even if it includes ideas from the others ;)

> Changelog v1->v2
> -Set explicity to NULL the "ctx->callback.sc" variable and return an error
>  code in "fw_iso_context_create" function if both callback parameters are
>  NULL as Lev R. Oshvang suggested.
> -Modify the commit changelog accordingly.
> 
> Changelog v2->v3
> -Put togeher all the work done in different patches by different authors.
> -Modify the previous work following the comments in the reviewed patches.
> 
> [1] https://lore.kernel.org/lkml/20200516173934.31527-1-oscar.carter@gmx.com/
> [2] https://lore.kernel.org/lkml/20200519173425.4724-1-oscar.carter@gmx.com/
> [3] https://lore.kernel.org/lkml/20200520064726.31838-1-o-takashi@sakamocchi.jp/
> [4] https://lore.kernel.org/lkml/20200524132048.243223-1-o-takashi@sakamocchi.jp/
> [5] https://lore.kernel.org/lkml/20200525015532.0055f9df@kant/
> 
>  drivers/firewire/core-cdev.c | 32 ++++++++++++++++++++++++++------
>  include/linux/firewire.h     | 11 +++++++----
>  2 files changed, 33 insertions(+), 10 deletions(-)

Anyway this patch looks good to me. I test this patch with libhinoko and
find no regression.

Reviewed-by: Takashi Sakamoto <o-takashi@...amocchi.jp>
Testeb-by: Takashi Sakamoto<o-takashi@...amocchi.jp>


[1] [RFT] ALSA control service programs for Digidesign Digi 002/003 family
and Tascam FireWire series
https://mailman.alsa-project.org/pipermail/alsa-devel/2020-July/170331.html

Thanks

Takashi Sakamoto