cephfs: replace copy-n-paste *_command functions argument handling

Similar to the functions in the rados pkg, cephfs package has a function
MdsCommand that is mostly boilerplate that to set up the C function's
arguments. Replace it with the types from the new cutil internal
package.

Signed-off-by: John Mulligan <jmulligan@redhat.com>

cephfs/command.go

@@ -10,6 +10,8 @@ import "C"
 
 import (
 	"unsafe"
+
+	"github.com/ceph/go-ceph/internal/cutil"
 )
 
 // MdsCommand sends commands to the specified MDS.
@@ -36,51 +38,22 @@ func (mount *MountInfo) MdsCommandWithInputBuffer(mdsSpec string, args [][]byte,
 func (mount *MountInfo) mdsCommand(mdsSpec string, args [][]byte, inputBuffer []byte) (buffer []byte, info string, err error) {
 	spec := C.CString(mdsSpec)
 	defer C.free(unsafe.Pointer(spec))
-
-	argc := len(args)
-	argv := make([]*C.char, argc)
-
-	for i, arg := range args {
-		argv[i] = C.CString(string(arg))
-	}
-	// free all array elements in a single defer
-	defer func() {
-		for i := range argv {
-			C.free(unsafe.Pointer(argv[i]))
-		}
-	}()
-
-	var (
-		outs, outbuf       *C.char
-		outslen, outbuflen C.size_t
-	)
-	inbuf := C.CString(string(inputBuffer))
-	inbufLen := len(inputBuffer)
-	defer C.free(unsafe.Pointer(inbuf))
+	ci := cutil.NewCommandInput(args, inputBuffer)
+	defer ci.Free()
+	co := cutil.NewCommandOutput()
+	defer co.Free()
 
 	ret := C.ceph_mds_command(
-		mount.mount,        // cephfs mount ref
-		spec,               // mds spec
-		&argv[0],           // cmd array
-		C.size_t(argc),     // cmd array length
-		inbuf,              // bulk input
-		C.size_t(inbufLen), // length inbuf
-		&outbuf,            // buffer
-		&outbuflen,         // buffer length
-		&outs,              // status string
-		&outslen)
-
-	if outslen > 0 {
-		info = C.GoStringN(outs, C.int(outslen))
-		C.free(unsafe.Pointer(outs))
-	}
-	if outbuflen > 0 {
-		buffer = C.GoBytes(unsafe.Pointer(outbuf), C.int(outbuflen))
-		C.free(unsafe.Pointer(outbuf))
-	}
-	if ret != 0 {
-		return nil, info, getError(ret)
-	}
-
-	return buffer, info, nil
+		mount.mount, // cephfs mount ref
+		spec,        // mds spec
+		(**C.char)(ci.Cmd()),
+		C.size_t(ci.CmdLen()),
+		(*C.char)(ci.InBuf()),
+		C.size_t(ci.InBufLen()),
+		(**C.char)(co.OutBuf()),
+		(*C.size_t)(co.OutBufLen()),
+		(**C.char)(co.Outs()),
+		(*C.size_t)(co.OutsLen()))
+	buf, status := co.GoValues()
+	return buf, status, getError(ret)
 }