linux-kernel - RE: [PATCH V3 4/4] x86/resctrl: Use appropriate API for strings terminated by newline

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Date:   Thu, 14 May 2020 15:06:31 -0500
From:   Babu Moger <babu.moger@....com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Reinette Chatre <reinette.chatre@...el.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "fenghua.yu@...el.com" <fenghua.yu@...el.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "kuo-lang.tseng@...el.com" <kuo-lang.tseng@...el.com>,
        "ravi.v.shankar@...el.com" <ravi.v.shankar@...el.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: RE: [PATCH V3 4/4] x86/resctrl: Use appropriate API for strings
 terminated by newline



> -----Original Message-----
> From: Andy Shevchenko <andy.shevchenko@...il.com>
> Sent: Thursday, May 14, 2020 2:11 PM
> To: Moger, Babu <Babu.Moger@....com>
> Cc: Reinette Chatre <reinette.chatre@...el.com>; tglx@...utronix.de;
> fenghua.yu@...el.com; bp@...en8.de; tony.luck@...el.com; kuo-
> lang.tseng@...el.com; ravi.v.shankar@...el.com; mingo@...hat.com;
> hpa@...or.com; x86@...nel.org; linux-kernel@...r.kernel.org; Andy
> Shevchenko <andriy.shevchenko@...ux.intel.com>
> Subject: Re: [PATCH V3 4/4] x86/resctrl: Use appropriate API for strings
> terminated by newline
> 
> On Thu, May 14, 2020 at 10:08 PM Babu Moger <babu.moger@....com>
> wrote:
> > > -----Original Message-----
> > > From: Reinette Chatre <reinette.chatre@...el.com>
> > > Sent: Wednesday, May 6, 2020 6:50 PM
> > > To: tglx@...utronix.de; fenghua.yu@...el.com; bp@...en8.de;
> > > tony.luck@...el.com
> > > Cc: kuo-lang.tseng@...el.com; ravi.v.shankar@...el.com;
> mingo@...hat.com;
> > > Moger, Babu <Babu.Moger@....com>; hpa@...or.com; x86@...nel.org;
> > > linux-kernel@...r.kernel.org; Reinette Chatre <reinette.chatre@...el.com>;
> > > Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > > Subject: [PATCH V3 4/4] x86/resctrl: Use appropriate API for strings
> terminated
> > > by newline
> > >
> > > 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.
> > >
> > > Suggested-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > > Signed-off-by: Reinette Chatre <reinette.chatre@...el.com>
> > > ---
> > >  arch/x86/kernel/cpu/resctrl/rdtgroup.c | 32 ++++++++++++++------------
> > >  1 file changed, 17 insertions(+), 15 deletions(-)
> > >
> > > diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > > b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > > index c60a3b307f7d..e70694892c02 100644
> > > --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > > +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> > > @@ -1408,12 +1408,11 @@ static ssize_t rdtgroup_mode_write(struct
> > > kernfs_open_file *of,
> > >  {
> > >       struct rdtgroup *rdtgrp;
> > >       enum rdtgrp_mode mode;
> > > -     int ret = 0;
> > > +     int user_m;
> > > +     int ret;
> >
> > This is bit confusing here. Mode and user_m should have been of same type.
> 
> It can't. If you compare enum to int you will need the explicit (weird) casting.

Ok. Got it. That is fine then.

> > You can define user_m to user_mode to be very clear.
> 
> > You can completely remove "mode" and directly use rdtgrp->mode instead. It
> > is left to you.
> >
> > > > -   /* Valid input requires a trailing newline */
> > > -     if (nbytes == 0 || buf[nbytes - 1] != '\n')
> > > +     if (nbytes == 0)
> > >               return -EINVAL;
> > > -     buf[nbytes - 1] = '\0';
> > >
> > >       rdtgrp = rdtgroup_kn_lock_live(of->kn);
> > >       if (!rdtgrp) {
> > > @@ -1425,11 +1424,17 @@ static ssize_t rdtgroup_mode_write(struct
> > > kernfs_open_file *of,
> > >
> > >       mode = rdtgrp->mode;
> > >
> > > -     if ((!strcmp(buf, "shareable") && mode == RDT_MODE_SHAREABLE) ||
> > > -         (!strcmp(buf, "exclusive") && mode == RDT_MODE_EXCLUSIVE) ||
> > > -         (!strcmp(buf, "pseudo-locksetup") &&
> > > -          mode == RDT_MODE_PSEUDO_LOCKSETUP) ||
> > > -         (!strcmp(buf, "pseudo-locked") && mode ==
> > > RDT_MODE_PSEUDO_LOCKED))
> > > +     ret = sysfs_match_string(rdt_mode_str, buf);
> > > +     if (ret < 0) {
> > > +             rdt_last_cmd_puts("Unknown or unsupported mode\n");
> > > +             goto out;
> > > +     }
> > > +
> > > +     user_m = ret;
> > > +     ret = 0;
> > > +
> > > +     /* Do nothing and return success if user asks for current mode */
> > > +     if (user_m == mode)
> > >               goto out;
> > >
> > >       if (mode == RDT_MODE_PSEUDO_LOCKED) {
> > > @@ -1438,14 +1443,14 @@ static ssize_t rdtgroup_mode_write(struct
> > > kernfs_open_file *of,
> > >               goto out;
> > >       }
> > >
> > > -     if (!strcmp(buf, "shareable")) {
> > > +     if (user_m == RDT_MODE_SHAREABLE) {
> > >               if (rdtgrp->mode == RDT_MODE_PSEUDO_LOCKSETUP) {
> > >                       ret = rdtgroup_locksetup_exit(rdtgrp);
> > >                       if (ret)
> > >                               goto out;
> > >               }
> > >               rdtgrp->mode = RDT_MODE_SHAREABLE;
> > > -     } else if (!strcmp(buf, "exclusive")) {
> > > +     } else if (user_m == RDT_MODE_EXCLUSIVE) {
> > >               if (!rdtgroup_mode_test_exclusive(rdtgrp)) {
> > >                       ret = -EINVAL;
> > >                       goto out;
> > > @@ -1456,14 +1461,11 @@ static ssize_t rdtgroup_mode_write(struct
> > > kernfs_open_file *of,
> > >                               goto out;
> > >               }
> > >               rdtgrp->mode = RDT_MODE_EXCLUSIVE;
> > > -     } else if (!strcmp(buf, "pseudo-locksetup")) {
> > > +     } else if (user_m == RDT_MODE_PSEUDO_LOCKSETUP) {
> > >               ret = rdtgroup_locksetup_enter(rdtgrp);
> > >               if (ret)
> > >                       goto out;
> > >               rdtgrp->mode = RDT_MODE_PSEUDO_LOCKSETUP;
> > > -     } else {
> > > -             rdt_last_cmd_puts("Unknown or unsupported mode\n");
> > > -             ret = -EINVAL;
> > >       }
> > >
> > >  out:
> > > --
> > > 2.21.0
> >
> 
> 
> --
> With Best Regards,
> Andy Shevchenko