Date:   Fri, 25 Nov 2022 10:44:01 -0800
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Cc:     Vladimir Oltean <vladimir.oltean@....com>,
        <netdev@...r.kernel.org>, "David S. Miller" <davem@...emloft.net>,
        "Eric Dumazet" <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        "Giuseppe Cavallaro" <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        Jose Abreu <joabreu@...opsys.com>,
        "Maxime Coquelin" <mcoquelin.stm32@...il.com>,
        Yang Yang <yang.yang29@....com>,
        "Xu Panda" <xu.panda@....com.cn>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] Revert "net: stmmac: use sysfs_streq() instead
 of strncmp()"

On Fri, 25 Nov 2022 12:58:23 +0100
Maciej Fijalkowski <maciej.fijalkowski@...el.com> wrote:

> On Fri, Nov 25, 2022 at 12:53:04PM +0200, Vladimir Oltean wrote:
> > This reverts commit f72cd76b05ea1ce9258484e8127932d0ea928f22.
> > This patch is so broken, it hurts. Apparently no one reviewed it and it
> > passed the build testing (because the code was compiled out), but it was
> > obviously never compile-tested, since it produces the following build
> > error, due to an incomplete conversion where an extra argument was left,
> > although the function being called was left:
> > 
> > stmmac_main.c: In function ‘stmmac_cmdline_opt’:
> > stmmac_main.c:7586:28: error: too many arguments to function ‘sysfs_streq’
> >  7586 |                 } else if (sysfs_streq(opt, "pause:", 6)) {
> >       |                            ^~~~~~~~~~~
> > In file included from ../include/linux/bitmap.h:11,
> >                  from ../include/linux/cpumask.h:12,
> >                  from ../include/linux/smp.h:13,
> >                  from ../include/linux/lockdep.h:14,
> >                  from ../include/linux/mutex.h:17,
> >                  from ../include/linux/notifier.h:14,
> >                  from ../include/linux/clk.h:14,
> >                  from ../drivers/net/ethernet/stmicro/stmmac/stmmac_main.c:17:
> > ../include/linux/string.h:185:13: note: declared here
> >   185 | extern bool sysfs_streq(const char *s1, const char *s2);
> >       |             ^~~~~~~~~~~
> > 
> > What's even worse is that the patch is flat out wrong. The stmmac_cmdline_opt()
> > function does not parse sysfs input, but cmdline input such as
> > "stmmaceth=tc:1,pause:1". The pattern of using strsep() followed by
> > strncmp() for such strings is not unique to stmmac, it can also be found
> > mainly in drivers under drivers/video/fbdev/.
> > 
> > With strncmp("tc:", 3), the code matches on the "tc:1" token properly.
> > With sysfs_streq("tc:"), it doesn't.
> > 
> > Fixes: f72cd76b05ea ("net: stmmac: use sysfs_streq() instead of strncmp()")
> > Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>  
> 
> Ah the infamous string handling in C...
> 
> Acked-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> 
> Even when there would be no build error I agree that we should have kept
> the code as it was.
> 
> > ---
> >  .../net/ethernet/stmicro/stmmac/stmmac_main.c  | 18 +++++++++---------
> >  1 file changed, 9 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > index 1a86e66e4560..3affb7d3a005 100644
> > --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> > @@ -7565,31 +7565,31 @@ static int __init stmmac_cmdline_opt(char *str)
> >  	if (!str || !*str)
> >  		return 1;
> >  	while ((opt = strsep(&str, ",")) != NULL) {
> > -		if (sysfs_streq(opt, "debug:")) {
> > +		if (!strncmp(opt, "debug:", 6)) {
> >  			if (kstrtoint(opt + 6, 0, &debug))
> >  				goto err;
> > -		} else if (sysfs_streq(opt, "phyaddr:")) {
> > +		} else if (!strncmp(opt, "phyaddr:", 8)) {
> >  			if (kstrtoint(opt + 8, 0, &phyaddr))
> >  				goto err;
> > -		} else if (sysfs_streq(opt, "buf_sz:")) {
> > +		} else if (!strncmp(opt, "buf_sz:", 7)) {
> >  			if (kstrtoint(opt + 7, 0, &buf_sz))
> >  				goto err;
> > -		} else if (sysfs_streq(opt, "tc:")) {
> > +		} else if (!strncmp(opt, "tc:", 3)) {
> >  			if (kstrtoint(opt + 3, 0, &tc))
> >  				goto err;
> > -		} else if (sysfs_streq(opt, "watchdog:")) {
> > +		} else if (!strncmp(opt, "watchdog:", 9)) {
> >  			if (kstrtoint(opt + 9, 0, &watchdog))
> >  				goto err;
> > -		} else if (sysfs_streq(opt, "flow_ctrl:")) {
> > +		} else if (!strncmp(opt, "flow_ctrl:", 10)) {
> >  			if (kstrtoint(opt + 10, 0, &flow_ctrl))
> >  				goto err;
> > -		} else if (sysfs_streq(opt, "pause:", 6)) {
> > +		} else if (!strncmp(opt, "pause:", 6)) {
> >  			if (kstrtoint(opt + 6, 0, &pause))
> >  				goto err;
> > -		} else if (sysfs_streq(opt, "eee_timer:")) {
> > +		} else if (!strncmp(opt, "eee_timer:", 10)) {
> >  			if (kstrtoint(opt + 10, 0, &eee_timer))
> >  				goto err;
> > -		} else if (sysfs_streq(opt, "chain_mode:")) {
> > +		} else if (!strncmp(opt, "chain_mode:", 11)) {
> >  			if (kstrtoint(opt + 11, 0, &chain_mode))
> >  				goto err;
> >  		}
> > -- 
> > 2.34.1
> >   

Configuring via module options is bad idea.
If you have to do it don't roll your own key/value parsing.
If the driver just used regular module_param() for this it wouldn't have this crap.

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