lib/fs: Fix and update error about inotify watch limit (fixes #4833) (#4835)

lib/fs/basicfs_test.go

@@ -7,14 +7,12 @@
 package fs
 
 import (
-	"errors"
 	"io/ioutil"
 	"os"
 	"path/filepath"
 	"runtime"
 	"sort"
 	"strings"
-	"syscall"
 	"testing"
 	"time"
 )
@@ -483,23 +481,3 @@ func TestRooted(t *testing.T) {
 		}
 	}
 }
-
-func TestWatchErrorLinuxInterpretation(t *testing.T) {
-	if runtime.GOOS != "linux" {
-		t.Skip("testing of linux specific error codes")
-	}
-
-	var errTooManyFiles syscall.Errno = 24
-	var errNoSpace syscall.Errno = 28
-
-	if !reachedMaxUserWatches(errTooManyFiles) {
-		t.Errorf("Errno %v should be recognised to be about inotify limits.", errTooManyFiles)
-	}
-	if !reachedMaxUserWatches(errNoSpace) {
-		t.Errorf("Errno %v should be recognised to be about inotify limits.", errNoSpace)
-	}
-	err := errors.New("Another error")
-	if reachedMaxUserWatches(err) {
-		t.Errorf("This error does not concern inotify limits: %#v", err)
-	}
-}

lib/fs/basicfs_watch.go

@@ -42,7 +42,7 @@ func (f *BasicFilesystem) Watch(name string, ignore Matcher, ctx context.Context
 	if err := notify.WatchWithFilter(filepath.Join(absName, "..."), backendChan, absShouldIgnore, eventMask); err != nil {
 		notify.Stop(backendChan)
 		if reachedMaxUserWatches(err) {
-			err = errors.New("failed to install inotify handler. Please increase inotify limits, see https://github.com/syncthing/syncthing-inotify#troubleshooting-for-folders-with-many-files-on-linux for more information")
+			err = errors.New("failed to setup inotify handler. Please increase inotify limits, see https://docs.syncthing.net/users/faq.html#inotify-limits")
 		}
 		return nil, err
 	}

lib/fs/basicfs_watch_errors_linux.go

@@ -8,11 +8,16 @@
 
 package fs
 
-import "syscall"
+import (
+	"os"
+	"syscall"
+)
 
 func reachedMaxUserWatches(err error) bool {
-	if errno, ok := err.(syscall.Errno); ok {
+	if pathErr, ok := err.(*os.PathError); ok {
+		if errno, ok := pathErr.Err.(syscall.Errno); ok {
 			return errno == 24 || errno == 28
 		}
+	}
 	return false
 }

lib/fs/basicfs_watch_test.go

@@ -10,11 +10,13 @@ package fs
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
 	"runtime"
 	"strconv"
+	"syscall"
 	"testing"
 	"time"
 
@@ -178,6 +180,34 @@ func TestWatchOverflow(t *testing.T) {
 	testScenario(t, name, testCase, expectedEvents, allowedEvents, "")
 }
 
+func TestWatchErrorLinuxInterpretation(t *testing.T) {
+	if runtime.GOOS != "linux" {
+		t.Skip("testing of linux specific error codes")
+	}
+
+	var errTooManyFiles = &os.PathError{
+		Op:   "error while traversing",
+		Path: "foo",
+		Err:  syscall.Errno(24),
+	}
+	var errNoSpace = &os.PathError{
+		Op:   "error while traversing",
+		Path: "bar",
+		Err:  syscall.Errno(28),
+	}
+
+	if !reachedMaxUserWatches(errTooManyFiles) {
+		t.Error("Underlying error syscall.Errno(24) should be recognised to be about inotify limits.")
+	}
+	if !reachedMaxUserWatches(errNoSpace) {
+		t.Error("Underlying error syscall.Errno(28) should be recognised to be about inotify limits.")
+	}
+	err := errors.New("Another error")
+	if reachedMaxUserWatches(err) {
+		t.Errorf("This error does not concern inotify limits: %#v", err)
+	}
+}
+
 // path relative to folder root, also creates parent dirs if necessary
 func createTestFile(name string, file string) string {
 	joined := filepath.Join(name, file)