Fix cgroup resolution to work on Debian distros.

Replaced the cgroup resolution function to work on Debian distributions
instead of just RHEL based ones. This implementation comes from the
Linux kernel tests.

lib/cgroup/cgroup.c

@@ -18,38 +18,52 @@ limitations under the License.
 
 #define _GNU_SOURCE
 #include <stdint.h>
+#include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
 
-// cgid_file_handle comes from bpftrace, see:
-// https://github.com/iovisor/bpftrace/blob/master/src/resolve_cgroupid.cpp
-struct cgid_file_handle {
-	unsigned int handle_bytes;
-	int handle_type;
-	uint64_t cgid;
-};
-
-// cgroup_id returns the ID of the given cgroup at path.
+// cgroup_id comes from get_cgroup_id in the Linux kernel.
+// https://github.com/torvalds/linux/commit/f269099a7e7a0c6732c4a817d0e99e92216414d9
 uint64_t cgroup_id(char *path)
 {
-    int ret;
-    int mount_id;
-    struct cgid_file_handle *handle;
-
-    handle = malloc(sizeof(struct cgid_file_handle));
-    if (handle == NULL) {
-        return 0;
-    }
-    handle->handle_bytes = sizeof(uint64_t);
-
-	ret = name_to_handle_at(AT_FDCWD, path, (struct file_handle *)handle, &mount_id, 0);
-    if (ret != 0) {
-        return 0;
+	int dirfd, err, flags, mount_id, fhsize;
+	union {
+		unsigned long long cgid;
+		unsigned char raw_bytes[8];
+	} id;
+	struct file_handle *fhp, *fhp2;
+	unsigned long long ret = 0;
+
+ 	dirfd = AT_FDCWD;
+	flags = 0;
+	fhsize = sizeof(*fhp);
+	fhp = calloc(1, fhsize);
+	if (!fhp) {
+		return 0;
+	}
+	err = name_to_handle_at(dirfd, path, fhp, &mount_id, flags);
+	if (err >= 0 || fhp->handle_bytes != 8) {
+		goto free_mem;
+	}
+
+ 	fhsize = sizeof(struct file_handle) + fhp->handle_bytes;
+	fhp2 = realloc(fhp, fhsize);
+	if (!fhp2) {
+		goto free_mem;
+	}
+	err = name_to_handle_at(dirfd, path, fhp2, &mount_id, flags);
+	fhp = fhp2;
+	if (err < 0) {
+		goto free_mem;
 	}
 
-    free(handle);
+ 	memcpy(id.raw_bytes, fhp->f_handle, 8);
+	ret = id.cgid;
 
-    return handle->cgid;
+ free_mem:
+	free(fhp);
+	return ret;
 }