Re: [igt-dev] [PATCH i-g-t v3] i915/perf: Find the associated perf-type for a particular device

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 14/01/2020 10:15, Chris Wilson wrote:
> Quoting Tvrtko Ursulin (2020-01-14 10:09:15)
>>
>> On 10/01/2020 11:53, Chris Wilson wrote:
>>> -uint64_t i915_type_id(void)
>>> +static char *bus_address(int i915, char *path, int pathlen)
>>> +{
>>> +     struct stat st;
>>> +     int len = -1;
>>> +     int dir;
>>> +     char *s;
>>> +
>>> +     if (fstat(i915, &st) || !S_ISCHR(st.st_mode))
>>> +             return NULL;
>>> +
>>> +     snprintf(path, pathlen, "/sys/dev/char/%d:%d",
>>> +              major(st.st_rdev), minor(st.st_rdev));
>>> +
>>> +     dir = open(path, O_RDONLY);
>>> +     if (dir != -1) {
>>> +             len = readlinkat(dir, "device", path, pathlen - 1);
>>> +             close(dir);
>>> +     }
>>> +     if (len < 0)
>>> +             return NULL;
>>> +
>>> +     path[len] = '\0';
>>
>> In the realm of hypothetical but an assert that no truncation occurred
>> would be good.
>>
>> if (len == pathlen - 1)
>>          return NULL;
>>
>> ?
>>
>> Although it is not clear to me from man readlinkat how do we distinguish
>> between truncation and exact fit.
>>
>> Or you were counting on failure at a later step if truncation occurred?
> 
> I did not expect a partial match to ever succeed. We at least know for
> the moment the names are fixed.
> 
>> Maybe try stat(2) in this wrapper to be sure function returns a valid path?
> 
> That would have the same danger of a partial match.

True, it would need more string validation - that the returned string 
matches the PCI bus address format of xxxx:yy:zz. Failure at a later 
step works for now I guess.

Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

> I think the foolproof solution here is having pmu_name in
> /sys/class/drm/cardN/pmu_name. (Or rather
> /sys/dev/char/%d:%d/device/pnu_name. :)

True.

Regards,

Tvrtko
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