Re: [PATCH V3 4/4] x86/resctrl: Use appropriate API for strings terminated by newline

[Andy Shevchenko]

On Thu, May 14, 2020 at 10:08 PM Babu Moger <babu.moger@xxxxxxx> wrote:
> > -----Original Message-----
> > From: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> > Sent: Wednesday, May 6, 2020 6:50 PM
> > To: tglx@xxxxxxxxxxxxx; fenghua.yu@xxxxxxxxx; bp@xxxxxxxxx;
> > tony.luck@xxxxxxxxx
> > Cc: kuo-lang.tseng@xxxxxxxxx; ravi.v.shankar@xxxxxxxxx; mingo@xxxxxxxxxx;
> > Moger, Babu <Babu.Moger@xxxxxxx>; hpa@xxxxxxxxx; x86@xxxxxxxxxx;
> > linux-kernel@xxxxxxxxxxxxxxx; Reinette Chatre <reinette.chatre@xxxxxxxxx>;
> > Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> > 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@xxxxxxxxxxxxxxx>
> > Signed-off-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> > ---
> >  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.

> 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