Re: [PATCH] ALSA: fireface: add field for the number of messages copied to user space

[Takashi Sakamoto <o-takashi@sakamocchi.jp>]

Hi,

On Fri, Feb 03, 2023 at 05:22:40PM +0100, Takashi Iwai wrote:
> On Thu, 02 Feb 2023 14:37:08 +0100,
> Takashi Sakamoto wrote:
> > 
> > Current structure includes no field to express the number of messages
> > copied to user space, thus user space application needs to information
> > out of the structure to parse the content of structure.
> > 
> > This commit adds a field to express the number of messages copied to user
> > space since It is more preferable to use self-contained structure.
> > 
> > Kees Cook proposed an idea of annotation for bound of flexible arrays
> > in his future improvement for flexible-length array in kernel. The
> > additional field for message count is suitable to the idea as well.
> > 
> > Reference: https://people.kernel.org/kees/bounded-flexible-arrays-in-c
> > Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
> 
> Wouldn't changing this break the existing application that talks with
> the older ABI?  Just to be sure...

You may well have the concern, indeed.

The structure is not exposed to user space yet, since it was added by a
commit ab811cfffa9 ("ALSA: fireface: update UAPI for data of knob
control"). It just exists in your (and mine) tree at present.


Thanks

Takashi Sakamoto