cephfs: add test cases for SelectFileystem call

These tests are all scoped within a test function that will only run if
the alternate fs name is supplied through the environment. This way the
tests can be run by hand on older versions if need be.

The tests verify the use of the SelectFilesystem function and that the
file systems are distinct namespaces.

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

cephfs/select_fs_test.go

@@ -0,0 +1,107 @@
+//go:build ceph_preview
+// +build ceph_preview
+
+package cephfs
+
+import (
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+var (
+	altFSName = ""
+)
+
+func init() {
+	altFSName = os.Getenv("GO_CEPH_TEST_ALT_FS_NAME")
+}
+
+func TestSelectFS(t *testing.T) {
+	if altFSName == "" {
+		t.Skip("no alternative fs provided")
+	}
+
+	t.Run("selectFilesystem", func(t *testing.T) {
+		mount, err := CreateMount()
+		assert.NoError(t, err)
+		assert.NotNil(t, mount)
+
+		err = mount.SelectFilesystem(altFSName)
+		assert.NoError(t, err)
+
+		assert.NoError(t, mount.Release())
+	})
+
+	t.Run("selectFilesystemError", func(t *testing.T) {
+		mount := fsConnect(t)
+		defer fsDisconnect(t, mount)
+
+		// already mounted - this should return an error
+		err := mount.SelectFilesystem(altFSName)
+		assert.Error(t, err)
+	})
+
+	t.Run("invalidName", func(t *testing.T) {
+		mount := fsConnect(t)
+		defer func() {
+			assert.NoError(t, mount.Release())
+		}()
+
+		assert.NoError(t, mount.Unmount())
+		// this call will not fail because the name isn't used until
+		// the file system is "mounted"
+		err := mount.SelectFilesystem("a.bunch-of~nonsense")
+		assert.NoError(t, err)
+
+		// this call is the one that fails because of the invalid name
+		assert.Error(t, mount.Mount())
+	})
+
+	t.Run("swapFS", func(t *testing.T) {
+		mount := fsConnect(t)
+		defer fsDisconnect(t, mount)
+
+		// create a file on the first file system
+		fname := "first_fs.txt"
+		f1, err := mount.Open(fname, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0644)
+		assert.NoError(t, err)
+		assert.NoError(t, f1.Close())
+		_, err = mount.Statx(fname, StatxBasicStats, 0)
+		assert.NoError(t, err)
+
+		// swap file systems - unmount, select fs, and then mount again
+		assert.NoError(t, mount.Unmount())
+		err = mount.SelectFilesystem(altFSName)
+		assert.NoError(t, err)
+		assert.NoError(t, mount.Mount())
+
+		// now we're on a new fs. stat'ing the file should fail, as the file is
+		// on the other file system
+		_, err = mount.Statx(fname, StatxBasicStats, 0)
+		assert.Error(t, err)
+
+		// verify that other operations on the 2nd fs work the same
+		fname2 := "second_fs.txt"
+		f2, err := mount.Open(fname2, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0644)
+		assert.NoError(t, err)
+		assert.NoError(t, f2.Close())
+		_, err = mount.Statx(fname2, StatxBasicStats, 0)
+		assert.NoError(t, err)
+		assert.NoError(t, mount.Unlink(fname2))
+
+		// swap back to the first file system
+		assert.NoError(t, mount.Unmount())
+		// first fs is always called cephfs for go-ceph tests
+		err = mount.SelectFilesystem("cephfs")
+		assert.NoError(t, err)
+		assert.NoError(t, mount.Mount())
+
+		// we're back on the first fs. see that the file still exists and then
+		// clean it up
+		_, err = mount.Statx(fname, StatxBasicStats, 0)
+		assert.NoError(t, err)
+		assert.NoError(t, mount.Unlink(fname))
+	})
+}