Message-ID: <108c63c753f2f637a72c2e105ac138f80d4b0859.camel@HansenPartnership.com>
Date: Tue, 03 Dec 2024 10:34:49 -0500
From: James Bottomley <James.Bottomley@...senPartnership.com>
To: Zijun Hu <zijun_hu@...oud.com>, Thomas Weißschuh
	 <thomas@...ch.de>
Cc: 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>, Philipp Zabel
 <p.zabel@...gutronix.de>, David Airlie <airlied@...il.com>, Simona Vetter
 <simona@...ll.ch>, Matthias Brugger <matthias.bgg@...il.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, Jean
 Delvare <jdelvare@...e.com>,  Guenter Roeck <linux@...ck-us.net>, Martin
 Tuma <martin.tuma@...iteqautomotive.com>, Mauro Carvalho Chehab
 <mchehab@...nel.org>, Andreas Noever <andreas.noever@...il.com>, Michael
 Jamet <michael.jamet@...el.com>, Mika Westerberg
 <mika.westerberg@...ux.intel.com>,  Yehezkel Bernat
 <YehezkelShB@...il.com>, Linus Walleij <linus.walleij@...aro.org>, Bartosz
 Golaszewski <brgl@...ev.pl>, Andrew Lunn <andrew@...n.ch>, Vladimir Oltean
 <olteanv@...il.com>,  "David S. Miller" <davem@...emloft.net>, Eric Dumazet
 <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
 <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, Dan Williams
 <dan.j.williams@...el.com>, Vishal Verma <vishal.l.verma@...el.com>, Dave
 Jiang <dave.jiang@...el.com>, Ira Weiny <ira.weiny@...el.com>, Takashi
 Sakamoto <o-takashi@...amocchi.jp>, Jiri Slaby <jirislaby@...nel.org>,
 Heikki Krogerus <heikki.krogerus@...ux.intel.com>, Srinivas Kandagatla
 <srinivas.kandagatla@...aro.org>, Lee Duncan <lduncan@...e.com>, Chris
 Leech <cleech@...hat.com>, Mike Christie <michael.christie@...cle.com>,
 "Martin K. Petersen" <martin.petersen@...cle.com>, Nilesh Javali
 <njavali@...vell.com>, Manish Rangankar <mrangankar@...vell.com>,
 GR-QLogic-Storage-Upstream@...vell.com, Davidlohr Bueso
 <dave@...olabs.net>, Jonathan Cameron <jonathan.cameron@...wei.com>, Alison
 Schofield <alison.schofield@...el.com>, Andreas Larsson
 <andreas@...sler.com>, Stuart Yoder <stuyoder@...il.com>, Laurentiu Tudor
 <laurentiu.tudor@....com>, Jens Axboe <axboe@...nel.dk>, Sudeep Holla
 <sudeep.holla@....com>, Cristian Marussi <cristian.marussi@....com>, Ard
 Biesheuvel <ardb@...nel.org>, Bjorn Andersson <andersson@...nel.org>,
 Mathieu Poirier <mathieu.poirier@...aro.org>, 
 linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
 linux-mediatek@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org, 
 linux-hwmon@...r.kernel.org, linux-media@...r.kernel.org, 
 linux-usb@...r.kernel.org, linux-gpio@...r.kernel.org,
 netdev@...r.kernel.org,  linux-pwm@...r.kernel.org, nvdimm@...ts.linux.dev,
  linux1394-devel@...ts.sourceforge.net, linux-serial@...r.kernel.org, 
 linux-sound@...r.kernel.org, open-iscsi@...glegroups.com, 
 linux-scsi@...r.kernel.org, linux-cxl@...r.kernel.org, 
 sparclinux@...r.kernel.org, linux-block@...r.kernel.org, 
 arm-scmi@...r.kernel.org, linux-efi@...r.kernel.org, 
 linux-remoteproc@...r.kernel.org, Zijun Hu <quic_zijuhu@...cinc.com>
Subject: Re: [PATCH v2 00/32] driver core: Constify API device_find_child()
 and adapt for various existing usages

On Tue, 2024-12-03 at 22:56 +0800, Zijun Hu wrote:
> On 2024/12/3 22:07, Thomas Weißschuh wrote:
> > 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.

That's way over complicated for this conversion: done properly there
should be no need for _Generic() compile time type matching at all.

> this way may fix building error issue but does not achieve our
> purpose. our purpose is that there are only constified
> device_find_child().
> 
> 
> > This also enables an incremental migration.
> 
> change the API prototype from:
> device_find_child(..., void *data_0, int (*match)(struct device *dev,
> void *data));
> 
> to:
> device_find_child(..., const void *data_0, int (*match)(struct device
> *dev, const void *data));
> 
> For @data_0,  void * -> const void * is okay.
> but for @match, the problem is function pointer type incompatibility.
> 
> there are two solutions base on discussions.
> 
> 1) squashing likewise Greg mentioned.
>    Do all of the "prep work" first, and then
>    do the const change at the very end, all at once.
> 
> 2)  as changing platform_driver's remove() prototype.
> Commit: e70140ba0d2b ("Get rid of 'remove_new' relic from platform
> driver struct")
> 
>  introduce extra device_find_child_new() which is constified  -> use
> *_new() replace ALL device_find_child() instances one by one -> 
> remove device_find_child() -> rename *_new() to device_find_child()
> once.

Why bother with the last step, which churns the entire code base again?
Why not call the new function device_find_child_const() and simply keep
it (it's descriptive of its function).  That way you can have a patch
series without merging and at the end simply remove the old function.

Regards,

James

Powered by blists - more mailing lists