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Date: Sun, 18 Sep 2016 17:52:17 -0700
From: Darren Hart <dvhart@...radead.org>
To: Giedrius Statkevičius
<giedrius.statkevicius@...il.com>
Cc: corentin.chary@...il.com, acpi4asus-user@...ts.sourceforge.net,
platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] asus-laptop: get rid of parse_arg()
On Sat, Sep 03, 2016 at 08:51:26AM +0300, Giedrius Statkevičius wrote:
> On Wed, Aug 17, 2016 at 11:23:15AM -0700, Darren Hart wrote:
> > On Tue, Aug 16, 2016 at 12:49:50PM +0300, Giedrius Statkevičius wrote:
> > > On Fri, Aug 12, 2016 at 02:40:02PM -0700, Darren Hart wrote:
> > > > On Sat, Aug 06, 2016 at 08:00:26PM +0300, Giedrius Statkevičius wrote:
> > > > > On Fri, Aug 05, 2016 at 04:15:07PM -0700, Darren Hart wrote:
> > > > > > On Fri, Aug 05, 2016 at 11:57:10PM +0300, Giedrius Statkevičius wrote:
> > > > > > > parse_arg() duplicates the funcionality of kstrtoint() so use the latter
> > > > > > > function instead. There is no funcionality change except that in the
> > > > > > > case of input being too big -ERANGE will be returned instead of -EINVAL
> > > > > > > which is not bad because -ERANGE makes more sense here. The check for
> > > > > > > !count is already done by the sysfs core so no need to duplicate it
> > > > > > > again. Also, add some minor corrections to error handling to accommodate
> > > > > > > the change in return values (parse_arg returned count if everything
> > > > > > > succeeded whereas kstrtoint returns 0 in the same situation)
> > > > > > >
> > > > > > > As a result of this patch asus-laptop.ko size is reduced by almost 1%:
> > > > > > > add/remove: 0/1 grow/shrink: 1/6 up/down: 1/-149 (-148)
> > > > > > > function old new delta
> > > > > > > __UNIQUE_ID_vermagic0 69 70 +1
> > > > > > > ls_switch_store 133 117 -16
> > > > > > > ledd_store 175 159 -16
> > > > > > > display_store 157 141 -16
> > > > > > > ls_level_store 193 176 -17
> > > > > > > gps_store 200 178 -22
> > > > > > > sysfs_acpi_set.isra 148 125 -23
> > > > > > > parse_arg.part 39 - -39
> > > > > > > Total: Before=19160, After=19012, chg -0.77%
> > > > > > >
> > > > > > > Signed-off-by: Giedrius Statkevičius <giedrius.statkevicius@...il.com>
> > > > > > > }
...
> > > > > > >
> > > > > > > /*
> > > > > > > @@ -975,15 +964,17 @@ static ssize_t ledd_store(struct device *dev, struct device_attribute *attr,
> > > > > > > struct asus_laptop *asus = dev_get_drvdata(dev);
> > > > > > > int rv, value;
> > > > > > >
> > > > > > > - rv = parse_arg(buf, count, &value);
> > > > > > > - if (rv > 0) {
> > > > > > > - if (write_acpi_int(asus->handle, METHOD_LEDD, value)) {
> > > > > > > - pr_warn("LED display write failed\n");
> > > > > > > - return -ENODEV;
> > > > > > > - }
> > > > > > > - asus->ledd_status = (u32) value;
> > > > > > > + rv = kstrtoint(buf, 0, &value);
> > > > > > > + if (rv < 0)
I was pointing out that for functional equivalence, this should be:
if (rv <= 0)
But as you point out below, this can't be achieved directly as kstrtoint returns
0 on success. I missed that in my first review (I guess), apologies.
> > > > > > > + return rv;
> > > > > > >
> > > > > >
> > > > > > This inverts the check to check for failure (this is preferred), but it does
> > > > > > change the successful path to include the value of 0, which was skipped over in
> > > > > > the original above.
> > > > > >
> > > > > > > + if (write_acpi_int(asus->handle, METHOD_LEDD, value)) {
> > > > > >
> > > > > > What is value if rv is 0? Perhaps safer/more explicit to test for (rv <= 0)
> > > > > > above. Please consider, and apply decision to all similar instances below.
> > > > > >
> > > > > Yes but in this case 0 indicates success so it doesn't make sense to test for <=
> > > > > 0 as it would be triggered on success. To be honest I didn't get the idea of
> > > > > what you wanted to say is wrong with this patch. Could you elaborate more?
> > > > >
> > > >
> > > > Your commit message states there is no functional change, but this changes the
> > > > behavior of this function (and others) for the 0 edge case.
> > > >
> > > > Previously if rv == 0, it would not call write_acpi_int(), now it will and set
> > > > the ledd_status.
> > > >
> > >
> > > sysfs already takes care of this edge case. parse_arg() returned 0 iff count ==
> > > 0 but in fs/sysfs/file.c sysfs_kf_write() there already is:
> > >
> > > if (!count)
> > > return 0;
> >
> > From a defensive programming context, we should be explicit in what we pass on
> > to other functions and not rely on the caller to filter for us, especially when
> > it's a simple matter of <= versus < in our comparison.
>
> Which comparison? kstrtoint returns 0 on success so we can't use <=.
>
> >
> > Please update the changed comparison sites in the patch to have the same end
> > result as before with respect to what it would do if a 0 were received.
> >
>
> So you want me to add:
>
> if (!count)
> return 0;
>
> Before each kstrtoint()? Sorry but I don't see a point in adding duplicated code
> that is not functional because these functions aren't and will never be used
> outside of sysfs. Just take a look at how many drivers in your own tree use
> kstrtoint() in sysfs methods and there isn't such check in place because it's
> pointless. Only samsung-laptop.c is an exception but it could be cleaned up
> because !count is a pointless check. Not only sysfs can't call us when count is
> 0 but kstrtoint() also returns -EINVAL if the string is empty (in case of the
> code in samsung-laptop).
You're correct.
Queued to testing. Thanks for taking the time to follow up. Sorry for the
hassle.
--
Darren Hart
Intel Open Source Technology Center
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