Re: [PATCH 2/2] x86/resctrl: Use appropriate API for strings terminated by newline

Andy Shevchenko
2020-04-02T13:06:29Z

On Wed, Apr 01, 2020 at 11:30:48AM -0700, Reinette Chatre 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.
>
> Suggested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
> ---
> arch/x86/kernel/cpu/resctrl/rdtgroup.c | 25 +++++++++++++------------
> 1 file changed, 13 insertions(+), 12 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> index fbee891a7d6e..623e33c0a290 100644
> --- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> +++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
> @@ -1412,11 +1412,11 @@ static ssize_t rdtgroup_mode_write(struct kernfs_open_file *of,
> struct rdtgroup *rdtgrp;
> enum rdtgrp_mode mode;
> int ret = 0;
> + int user_m;
>

> /* Valid input requires a trailing newline */
> if (nbytes == 0 || buf[nbytes - 1] != '\n')
> return -EINVAL;
> - buf[nbytes - 1] = '\0';

The above test is not needed and comment now is misleading.
WRT nbytes I believe that kernel fs code checks for that.

> rdtgrp = rdtgroup_kn_lock_live(of->kn);
> if (!rdtgrp) {
> @@ -1428,11 +1428,15 @@ 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))
> + user_m = sysfs_match_string(rdt_mode_str, buf);
> + if (user_m < 0) {
> + rdt_last_cmd_puts("Unknown or unsupported mode\n");
> + ret = user_m;
> + goto out;
> + }

You can do it the way

ret = sysfs_match_string(...);
if (ret < 0) {
...
}
user_m = ret;

> + /* Do nothing and return success if user asks for current mode */
> + if (user_m == mode)
> goto out;
>
> if (mode == RDT_MODE_PSEUDO_LOCKED) {
> @@ -1441,14 +1445,14 @@ 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;
> @@ -1459,14 +1463,11 @@ 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