Fix issue with marking mount point

- Fix mark validation for marking mount point
- Fix issue in readEvent loop to increment metadata when fd != NO_FD
  case
- Update package documentation
- Update README

Author: opcoder0

README.md

@@ -12,7 +12,7 @@ fanotify has features spanning different kernel versions -
 - For Linux kernel versions 5.1 - 5.8 additional information about the underlying filesystem object is correlated to an event.
 - For Linux kernel version 5.9 or later the modified file name is made available in the event.
 
-## Example: Listener watching for events
+## Example: Listener watching for events on a directory
 
 ```
 package main
@@ -76,6 +76,53 @@ func main() {
 }
 ```
 
+## Example: Listener watching for events on a mount point
+
+```
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+
+	"github.com/opcoder0/fanotify"
+)
+
+func main() {
+	var mountPoint string
+
+	flag.StringVar(&mountPoint, "mount-path", "", "mount point path")
+	flag.Parse()
+
+	if mountPoint == "" {
+		fmt.Println("missing mount path")
+		os.Exit(1)
+	}
+	listener, err := fanotify.NewListener(mountPoint, true)
+	if err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+	fmt.Println("Listening to events for:", mountPoint)
+	var eventTypes fanotify.EventType
+	eventTypes = fanotify.FileAccessed |
+			fanotify.FileOrDirectoryAccessed |
+			fanotify.FileModified |
+			fanotify.FileOpenedForExec |
+			fanotify.FileOpened
+	err = listener.MarkMount(eventTypes, false)
+	if err != nil {
+		fmt.Println("MarkMount:", err)
+		os.Exit(1)
+	}
+	go listener.Start()
+	for event := range listener.Events {
+		fmt.Println(event)
+	}
+	listener.Stop()
+}
+```
 ## Known Issues
 
 Certain flag combinations / event types cause issues with event reporting.

fanotify_api.go

@@ -74,9 +74,11 @@ type Listener struct {
 // multiple listener instances need to be used.
 //
 // mountPoint can be any file/directory under the mount point being watched.
-// Passing "true" to the entireMount parameter monitors the entire mount point for marked
-// events. Passing "false" allows specifying multiple paths (files/directories)
-// under this mount point for monitoring filesystem events.
+// entireMount when "true" monitors the entire mount point for marked
+// events which includes all directories, subdirectories, and the
+// contained files of the mount point. Passing "false" allows specifying
+// multiple paths (files/directories)
+// under this mount point for monitoring filesystem events using AddWatch.
 //
 // The function returns a new instance of the listener. The fanotify flags are set
 // based on the running kernel version. [ErrCapSysAdmin] is returned if the process does not
@@ -150,17 +152,26 @@ func (l *Listener) Stop() {
 // mount point. Passing true to remove, removes the mark from the mount point.
 // This method returns an [ErrWatchPath] if the listener was not initialized to monitor
 // the entire mount point. To mark specific files or directories use [AddWatch] method.
-// The entire mount cannot be monitored for the following events:
-// [FileCreated], [FileAttribChanged], [FileMovedFrom], [FileMovedTo], [WatchedFileDeleted]
-// Passing any of these flags in eventTypes will return [ErrInvalidFlagCombination] error
+// The entire mount cannot be monitored for any events for which new directory modification
+// events are provided. Passing any of these directory modification flags in eventTypes
+// will return [ErrInvalidFlagCombination] error. Valid eventTypes are
+// [FileAccessed], [FileOrDirectoryAccessed], [FileModified], [FileOpenedForExec]
+// [FileOpened], [FileOrDirectoryOpened].
 func (l *Listener) MarkMount(eventTypes EventType, remove bool) error {
 	if l.entireMount == false {
 		return ErrWatchPath
 	}
-	if eventTypes.Has(FileCreated) ||
-		eventTypes.Has(FileAttribChanged) ||
-		eventTypes.Has(FileMovedFrom) ||
+	if eventTypes.Has(FileAttribChanged) ||
+		eventTypes.Has(FileOrDirectoryAttribChanged) ||
+		eventTypes.Has(FileCreated) ||
+		eventTypes.Has(FileOrDirectoryCreated) ||
+		eventTypes.Has(FileDeleted) ||
+		eventTypes.Has(FileOrDirectoryDeleted) ||
+		eventTypes.Has(WatchedFileDeleted) ||
+		eventTypes.Has(WatchedFileOrDirectoryDeleted) ||
 		eventTypes.Has(FileMovedTo) ||
+		eventTypes.Has(FileMovedFrom) ||
+		eventTypes.Has(WatchedFileMoved) ||
 		eventTypes.Has(WatchedFileDeleted) {
 		return ErrInvalidFlagCombination
 	}

fanotify_event.go

@@ -385,6 +385,9 @@ func (l *Listener) readEvents() error {
 					Pid:        int(metadata.Pid),
 				}
 				l.Events <- event
+				i += int(metadata.Event_len)
+				n -= int(metadata.Event_len)
+				metadata = (*unix.FanotifyEventMetadata)(unsafe.Pointer(&buf[i]))
 			} else {
 				// fid (applicable to kernels 5.1+)
 				fid = (*fanotifyEventInfoFID)(unsafe.Pointer(&buf[i+int(metadata.Metadata_len)]))