cephfs: add a UserPerm type wrapping libcephfs UserPerm

The UserPerm type will be used later to set the owner credentials on the
mount.

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

cephfs/userperm.go

@@ -0,0 +1,72 @@
+package cephfs
+
+/*
+#cgo LDFLAGS: -lcephfs
+#cgo CPPFLAGS: -D_FILE_OFFSET_BITS=64
+#include <cephfs/libcephfs.h>
+*/
+import "C"
+
+import (
+	"runtime"
+	"unsafe"
+)
+
+// UserPerm types may be used to get or change the credentials used by the
+// connection or some operations.
+type UserPerm struct {
+	userPerm *C.UserPerm
+
+	// cache create-time params
+	managed bool // if set, the userPerm was created by go-ceph
+	uid     C.uid_t
+	gid     C.gid_t
+	gidList []C.gid_t
+}
+
+// NewUserPerm creates a UserPerm pointer and the underlying ceph resources.
+//
+// Implements:
+//  UserPerm *ceph_userperm_new(uid_t uid, gid_t gid, int ngids, gid_t *gidlist);
+func NewUserPerm(uid, gid int, gidlist []int) *UserPerm {
+	// the C code does not copy the content of the gid list so we keep the
+	// inputs stashed in the go type. For completeness we stash everything.
+	p := &UserPerm{
+		managed: true,
+		uid:     C.uid_t(uid),
+		gid:     C.gid_t(gid),
+		gidList: make([]C.gid_t, len(gidlist)),
+	}
+	var cgids *C.gid_t
+	if len(p.gidList) > 0 {
+		for i, gid := range gidlist {
+			p.gidList[i] = C.gid_t(gid)
+		}
+		cgids = (*C.gid_t)(unsafe.Pointer(&p.gidList[0]))
+	}
+	p.userPerm = C.ceph_userperm_new(
+		p.uid, p.gid, C.int(len(p.gidList)), cgids)
+	// if the go object is unreachable, we would like to free the c-memory
+	// since this has no other resources than memory associated with it.
+	// This is only valid for UserPerm objects created by new, and thus have
+	// the managed var set.
+	runtime.SetFinalizer(p, destroyUserPerm)
+	return p
+}
+
+// Destroy will explicitly free ceph resources associated with the UserPerm.
+//
+// Implements:
+//  void ceph_userperm_destroy(UserPerm *perm);
+func (p *UserPerm) Destroy() {
+	if p.userPerm == nil || !p.managed {
+		return
+	}
+	C.ceph_userperm_destroy(p.userPerm)
+	p.userPerm = nil
+	p.gidList = nil
+}
+
+func destroyUserPerm(p *UserPerm) {
+	p.Destroy()
+}

cephfs/userperm_test.go

@@ -0,0 +1,43 @@
+package cephfs
+
+import (
+	"runtime"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestUserPerm(t *testing.T) {
+	t.Run("newAndDestroy", func(t *testing.T) {
+		uperm := NewUserPerm(0, 0, nil)
+		assert.NotNil(t, uperm)
+		assert.Equal(t, 0, len(uperm.gidList))
+		assert.True(t, uperm.managed)
+
+		// Destroy should be idempotent in our go library
+		uperm.Destroy()
+		uperm.Destroy()
+	})
+	t.Run("notManagedDestroy", func(t *testing.T) {
+		uperm := &UserPerm{}
+		assert.False(t, uperm.managed)
+		// Calling destroy shouldn't do much but is safe to call (many times)
+		uperm.Destroy()
+		uperm.Destroy()
+	})
+	t.Run("tryForceGc", func(t *testing.T) {
+		func() {
+			uperm := NewUserPerm(0, 0, nil)
+			_ = uperm
+		}()
+		runtime.GC()
+	})
+	t.Run("gidList", func(t *testing.T) {
+		uperm := NewUserPerm(1000, 1000, []int{1028, 1192, 2112})
+		defer uperm.Destroy()
+		assert.Equal(t, 3, len(uperm.gidList))
+		assert.EqualValues(t, 1028, uperm.gidList[0])
+		assert.EqualValues(t, 1192, uperm.gidList[1])
+		assert.EqualValues(t, 2112, uperm.gidList[2])
+	})
+}