cephfs: add wrapper funcs for ceph_mds_command

Adding a wrapper for ceph_mds_command allows the client to make
queries against the mds server.

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

cephfs/cephfs.go

@@ -160,3 +160,76 @@ func (mount *MountInfo) IsMounted() bool {
 	ret := C.ceph_is_mounted(mount.mount)
 	return ret == 1
 }
+
+// MdsCommand sends commands to the specified MDS.
+func (mount *MountInfo) MdsCommand(mdsSpec string, args [][]byte) ([]byte, string, error) {
+	return mount.mdsCommand(mdsSpec, args, nil)
+}
+
+// MdsCommandWithInputBuffer sends commands to the specified MDS, with an input
+// buffer.
+func (mount *MountInfo) MdsCommandWithInputBuffer(mdsSpec string, args [][]byte, inputBuffer []byte) ([]byte, string, error) {
+	return mount.mdsCommand(mdsSpec, args, inputBuffer)
+}
+
+// mdsCommand supports sending formatted commands to MDS.
+//
+// Implements:
+//  int ceph_mds_command(struct ceph_mount_info *cmount,
+//      const char *mds_spec,
+//      const char **cmd,
+//      size_t cmdlen,
+//      const char *inbuf, size_t inbuflen,
+//      char **outbuf, size_t *outbuflen,
+//      char **outs, size_t *outslen);
+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))
+
+	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
+}

cephfs/cephfs_test.go

@@ -1,6 +1,7 @@
 package cephfs
 
 import (
+	"encoding/json"
 	"fmt"
 	"os"
 	"syscall"
@@ -236,3 +237,34 @@ func TestCreateMountWithId(t *testing.T) {
 	err = mount.Mount()
 	assert.NoError(t, err)
 }
+
+func TestMdsCommand(t *testing.T) {
+	mount := fsConnect(t)
+
+	cmd := []byte(`{"prefix": "client ls"}`)
+	buf, info, err := mount.MdsCommand(
+		"Z", // TODO: fix hard-coded name mds (from ci container script)
+		[][]byte{cmd})
+	assert.NoError(t, err)
+	assert.NotEqual(t, "", string(buf))
+	assert.Equal(t, "", string(info))
+	assert.Contains(t, string(buf), "ceph_version")
+	// response should also be valid json
+	var j []interface{}
+	err = json.Unmarshal(buf, &j)
+	assert.NoError(t, err)
+	assert.GreaterOrEqual(t, len(j), 1)
+}
+
+func TestMdsCommandError(t *testing.T) {
+	mount := fsConnect(t)
+
+	cmd := []byte("iAMinValId~~~")
+	buf, info, err := mount.MdsCommand(
+		"Z", // TODO: fix hard-coded name mds (from ci container script)
+		[][]byte{cmd})
+	assert.Error(t, err)
+	assert.Equal(t, "", string(buf))
+	assert.NotEqual(t, "", string(info))
+	assert.Contains(t, string(info), "unparseable JSON")
+}