linux-kernel - Re: [PATCH V5 4/4] x86/resctrl: Use appropriate API for strings terminated by newline

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Date:   Tue, 19 May 2020 19:07:10 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Reinette Chatre <reinette.chatre@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Tony Luck <tony.luck@...el.com>, kuo-lang.tseng@...el.com,
        ravi.v.shankar@...el.com, Ingo Molnar <mingo@...hat.com>,
        Babu Moger <babu.moger@....com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V5 4/4] x86/resctrl: Use appropriate API for strings
 terminated by newline

On Tue, May 19, 2020 at 08:50:22AM -0700, Reinette Chatre wrote:
> On 5/19/2020 1:28 AM, Andy Shevchenko wrote:
> > On Tue, May 19, 2020 at 2:50 AM Reinette Chatre
> > <reinette.chatre@...el.com> wrote:

...

> >> +       ret = sysfs_match_string(rdt_mode_str, buf);
> >> +       if (ret < 0) {
> >> +               rdt_last_cmd_puts("Unknown or unsupported mode\n");
> >> +               ret = -EINVAL;
> >> +               goto out;
> >> +       }
> 
> From your previous email ...
> 
> >> +       ret = sysfs_match_string(rdt_mode_str, buf);
> >> +       if (ret < 0) {
> >> +               rdt_last_cmd_puts("Unknown or unsupported mode\n");
> >
> >> +               ret = -EINVAL;
> >
> > This is redundant.
> 
> I understand that shadowing an error code is generally of concern. In
> this case the error code is set to -EINVAL to ensure that it is the same
> error code that was returned to user space originally and will continue
> to be so no matter what changes may come to sysfs_match_string().

It returns -EINVAL and if that will be ever changed this driver would be one of
hundreds who suffers.

...

> > Can't we unify latter with a former like ...

> This would have been ideal if done from the start but currently "0" is
> returned if the current mode is pseudo-locked and user attempts to
> change the mode to pseudo-locked. Thus, to maintain the current user
> interface the check if user wants to set pseudo-locked mode is moved
> after the check if new mode is same as existing mode and thus not
> unified because that will result in an error returned always when user
> requests pseudo-locked mode.

Ah, I see now.

But we can then drop the check from sysfs_match_string() returned value, like

	user_m = sysfs_match_string();
	if (...) {
		...
	} else { // w/o even checking for the PSEUDO_LOCKED
		...
		goto out;
	}

Can we?

-- 
With Best Regards,
Andy Shevchenko