cephfs: Add a separate test file for fallocate with mode 0

There are backports created for fallocate API changes[1] that got merged
recently. Considering the time taken for these backports to get in to
release branches and finally as a released version we create a separate
test file to have more fine grained control over various pre-release CI
jobs with the help of corresponding build tags.

Modification of build tags should go hand-in-hand with the version
detection logic used in file_test.go once a backport is available in
released version.

[1] ceph/ceph#59725

Signed-off-by: Anoop C S <anoopcs@cryptolab.net>

cephfs/errors.go

@@ -37,6 +37,9 @@ var (
 	ErrNotConnected = getError(-C.ENOTCONN)
 	// ErrNotExist indicates a non-specific missing resource.
 	ErrNotExist = getError(-C.ENOENT)
+	// ErrOpNotSupported is returned in general for operations that are not
+	// supported.
+	ErrOpNotSupported = getError(-C.EOPNOTSUPP)
 
 	// Private errors:
 

cephfs/file_fallocate_mode_zero_unsupported_test.go

@@ -0,0 +1,30 @@
+//go:build main
+
+package cephfs
+
+import (
+	"os"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+// TestFallocateModeZeroUnsupported and this test file exists merely to track
+// the backports for https://tracker.ceph.com/issues/68026. Once they are
+// available with release versions this can probably vanish.
+func TestFallocateModeZeroUnsupported(t *testing.T) {
+	mount := fsConnect(t)
+	defer fsDisconnect(t, mount)
+	fname := "file1.txt"
+	f, err := mount.Open(fname, os.O_RDWR|os.O_CREATE, 0644)
+	assert.NoError(t, err)
+	assert.NotNil(t, f)
+	defer func() {
+		assert.NoError(t, f.Close())
+		assert.NoError(t, mount.Unlink(fname))
+	}()
+
+	err = f.Fallocate(FallocNoFlag, 0, 10)
+	assert.Error(t, err)
+	assert.Equal(t, ErrOpNotSupported, err)
+}