[RESEND PATCH 07/12] golang/xenlight: add logging conveniences for within xenlight

[Nick Rosbrook <rosbrookn@xxxxxxxxx>]

Add some logging methods to Context to provide easy use of the
Contenxt's xentoollog_logger. These are not exported, but the LogLevel
type is so that a later commit can allow the Context's log level to be
configurable.

Becuase cgo does not support calling C functions with variable
arguments, e.g. xtl_log, add an xtl_log_wrap function to the cgo preamble
that accepts an already formatted string, and handle the formatting in
Go.

Signed-off-by: Nick Rosbrook <rosbrookn@xxxxxxxxxxxx>
---
 tools/golang/xenlight/xenlight.go | 45 +++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/tools/golang/xenlight/xenlight.go 
b/tools/golang/xenlight/xenlight.go
index fc3eb0bf3f..f68d7b6e97 100644
--- a/tools/golang/xenlight/xenlight.go
+++ b/tools/golang/xenlight/xenlight.go
@@ -32,6 +32,15 @@ static const libxl_childproc_hooks childproc_hooks = { 
.chldowner = libxl_sigchl
 void xenlight_set_chldproc(libxl_ctx *ctx) {
        libxl_childproc_setmode(ctx, &childproc_hooks, NULL);
 }
+
+void xtl_log_wrap(struct xentoollog_logger *logger,
+                 xentoollog_level level,
+                 int errnoval,
+                 const char *context,
+                 const char *msg)
+{
+    xtl_log(logger, level, errnoval, context, "%s", msg);
+}
 */
 import "C"
 
@@ -192,6 +201,42 @@ func (ctx *Context) Close() error {
        return nil
 }
 
+// LogLevel represents an xentoollog_level, and can be used to configre the log
+// level of a Context's logger.
+type LogLevel int
+
+const (
+       //LogLevelNone     LogLevel = C.XTL_NONE
+       LogLevelDebug    LogLevel = C.XTL_DEBUG
+       LogLevelVerbose  LogLevel = C.XTL_VERBOSE
+       LogLevelDetail   LogLevel = C.XTL_DETAIL
+       LogLevelProgress LogLevel = C.XTL_PROGRESS
+       LogLevelInfo     LogLevel = C.XTL_INFO
+       LogLevelNotice   LogLevel = C.XTL_NOTICE
+       LogLevelWarn     LogLevel = C.XTL_WARN
+       LogLevelError    LogLevel = C.XTL_ERROR
+       LogLevelCritical LogLevel = C.XTL_CRITICAL
+       //LogLevelNumLevels LogLevel = C.XTL_NUM_LEVELS
+)
+
+func (ctx *Context) log(lvl LogLevel, errnoval int, format string, a 
...interface{}) {
+       msg := C.CString(fmt.Sprintf(format, a...))
+       defer C.free(unsafe.Pointer(msg))
+       context := C.CString("xenlight")
+       defer C.free(unsafe.Pointer(context))
+
+       C.xtl_log_wrap((*C.xentoollog_logger)(unsafe.Pointer(ctx.logger)),
+               C.xentoollog_level(lvl), C.int(errnoval), context, msg)
+}
+
+func (ctx *Context) logd(format string, a ...interface{}) {
+       ctx.log(LogLevelDebug, -1, format, a...)
+}
+
+func (ctx *Context) logw(format string, a ...interface{}) {
+       ctx.log(LogLevelWarn, -1, format, a...)
+}
+
 /*
  * Types: Builtins
  */
-- 
2.17.1