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

Reinette Chatre
2020-04-02T21:19:12Z

Hi Andy,

(Your two responses have been merged)

On 4/2/2020 6:06 AM, Andy Shevchenko wrote:
> 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;
>>

>
> ...and forgot to mention this...
>
> int user_m;
> int ret;
>

>
>> /* 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.

If nbytes is 0 it is still passed to this function. You are correct that
those tests are not needed though (if nbytes is 0 then
sysfs_match_string() will not find a match and return EINVAL via that path).

Thank you for catching this. I'll remove those unnecessary checks.

>
>> 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;
>
> ...and this changes
>
> ret = 0;
>
>

ok, I'll do it this way in the next version.

Thank you

Reinette