eve/watcher: display warning if parent directory not readable

The user may point EveBox at files in a directory that is not
readable. If the parent directory of the files are not readable,
display a warning.

src/eve/watcher.rs

@@ -42,6 +42,18 @@ impl EvePatternWatcher {
 
     pub fn check(&mut self) {
         for pattern in &self.patterns {
+            // This is for error reporting to the user, in the case
+            // where the parent directory of the log files is not
+            // readable by EveBox.
+            if let Some(p) = PathBuf::from(pattern).parent() {
+                if let Err(err) = std::fs::read_dir(p) {
+                    warn!(
+                        "Failed to read directory {}, EVE log files are likely unreadable: {}",
+                        p.display(),
+                        err
+                    );
+                }
+            }
             if let Ok(paths) = crate::path::expand(pattern) {
                 for path in paths {
                     if !self.filenames.contains(&path) {