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 11:19:36 +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>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH V5 4/4] x86/resctrl: Use appropriate API for strings
 terminated by newline

On Tue, May 19, 2020 at 2:50 AM Reinette Chatre
<reinette.chatre@...el.com> wrote:
>
> The user input to files in the resctrl filesystem are expected to be
> terminated with a newline. Testing the user input includes a test for
> the presence of a newline and then replacing the newline with NUL
> byte followed by comparison using strcmp().
>
> sysfs_streq() exists to test if strings are equal, treating both NUL and
> newline-then-NUL as equivalent string terminations. Even more,
> sysfs_match_string() exists to match a given string in an array using
> sysfs_streq().
>
> Replace existing strcmp() comparisons of strings that are terminated
> with a newline with more appropriate sysfs_streq() via the
> sysfs_match_string() API that can perform the match across the different
> mode strings that are already maintained in an array.

...

> Changes since V4:
> - Remove "mode" local variable from rdtgroup_mode_write(). This variable
>   was previously used to create shorter lines with the original strcmp()
>   code that was removed in patch 4/4.
> - Andy pointed out that the repeated assignment to rdtgrp->mode could be
>   replaced by a single assignment after all the checks. This was initially
>   rejected because it would let the "RDT_MODE_PSEUDO_LOCKED" assignment
>   slip through. Even so, Andy's feedback revealed that the new changes
>   unintentionally let a user's attempt at setting the mode to pseudo-locked
>   be silently ignored where it previously reported an error. Restore original
>   user space behavior by returning success when user attempts to change any
>   mode when it is already the current mode (including pseudo-locked) and
>   returning failure when user attempts to set the mode to pseudo-locked.
>   After this change it is possible to follow Andy's original suggestion
>   of using a single assignment. (Andy)

Glad we can do it!

...

> +       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.

> +               goto out;
> +       }

-- 
With Best Regards,
Andy Shevchenko