netdev - Re: [PATCH v2 00/32] driver core: Constify API device_find_child() and adapt for various existing usages

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Message-ID: <8fb887a0-3634-4e07-9f0d-d8d7c72ca802@t-8ch.de>
Date: Tue, 3 Dec 2024 15:07:55 +0100
From: Thomas Weißschuh <thomas@...ch.de>
To: James Bottomley <James.Bottomley@...senpartnership.com>
Cc: Zijun Hu <zijun_hu@...oud.com>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Uwe Kleine-König <ukleinek@...nel.org>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Chun-Kuang Hu <chunkuang.hu@...nel.org>, 
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Subject: Re: [PATCH v2 00/32] driver core: Constify API device_find_child()
 and adapt for various existing usages

On 2024-12-03 08:58:26-0500, James Bottomley wrote:
> On Tue, 2024-12-03 at 21:02 +0800, Zijun Hu wrote:
> > On 2024/12/3 20:41, Greg Kroah-Hartman wrote:
> > > On Tue, Dec 03, 2024 at 08:23:45PM +0800, Zijun Hu wrote:
> [...]
> > > > or squash such patch series into a single patch ?
> > > > 
> > > > various subsystem maintainers may not like squashing way.
> > > 
> > > Agreed, so look into either doing it in a bisectable way if at all
> > > possible.  As I don't see a full series here, I can't suggest how
> > > it needs to happen :(
> > > 
> > 
> > let me send you a full series later and discuss how to solve this
> > issue.
> 
> It's only slightly more complex than what we normally do: modify all
> instances and then change the API.  In this case you have an additional
> problem because the prototype "const void *" will cause a mismatch if a
> function has "void *".  The easiest way to solve this is probably to
> make device_find_child a macro that coerces its function argument to
> having a non const "void *" and then passes off to the real function. 
> If you do that in the first patch, then you can constify all the
> consumers and finally remove the macro coercion in the last patch.

Casting function pointers like that should be detected and trapped by
control flow integrity checking (KCFI).

Another possibility would be to use a macro and _Generic to dispatch to
two different backing functions. See __BIN_ATTR() in
include/linux/sysfs.h for an inspiration.
This also enables an incremental migration.


Thomas