SetAPI: embed rc into error

In case seccomp_api_set() failed, embed its return code into the error
(rather than merely adding -N text into it), so that a user can check
for a particular error using e.g. errors.Is(err, syscall.EINVAL).

Do not embed EOPNOTSUPP since this is not what libseccomp returns
(this is returned by own code in case it is compiled with old (< 2.4.0)
libseccomp headers).

Acked-by: Tom Hromatka <[email protected]>
Signed-off-by: Kir Kolyshkin <[email protected]>

Author: kolyshkin

seccomp_internal.go

@@ -349,11 +349,12 @@ func getAPI() (uint, error) {
 // Set the API level
 func setAPI(api uint) error {
 	if retCode := C.seccomp_api_set(C.uint(api)); retCode != 0 {
-		if errRc(retCode) == syscall.EOPNOTSUPP {
+		e := errRc(retCode)
+		if e == syscall.EOPNOTSUPP {
 			return fmt.Errorf("API level operations are not supported")
 		}
 
-		return fmt.Errorf("could not set API level: %v", retCode)
+		return fmt.Errorf("could not set API level: %w", e)
 	}
 
 	return nil