Allow recrusive generic error

Error sent from child process is already genericError, if
we don't allow recrusive generic error, we won't get any
cause infomation from parent process.

Before, we got:
WARN[0000] exit status 1
ERRO[0000] operation not permitted

After, we got:
WARN[0000] exit status 1
ERRO[0000] container_linux.go:247: starting container process caused "process_linux.go:359: container init caused \"operation not permitted\""

it's not pretty but useful for detecting root causes.

Signed-off-by: Qiang Huang <[email protected]>

Author: hqhq

libcontainer/generic_error.go

@@ -67,9 +67,6 @@ func newSystemErrorWithCause(err error, cause string) Error {
 // stack frames skipped. This is only to be called by the other functions for
 // formatting the error.
 func createSystemError(err error, cause string) Error {
-	if le, ok := err.(Error); ok {
-		return le
-	}
 	gerr := &genericError{
 		Timestamp: time.Now(),
 		Err:       err,

libcontainer/process_linux.go

@@ -356,7 +356,7 @@ loop:
 		}
 	}
 	if !sentRun {
-		return newSystemErrorWithCause(ierr, "container init failed")
+		return newSystemErrorWithCause(ierr, "container init")
 	}
 	if p.config.Config.Namespaces.Contains(configs.NEWNS) && !sentResume {
 		return newSystemError(fmt.Errorf("could not synchronise after executing prestart hooks with container process"))