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.
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. :)
-Chris
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