Restart monitor view when files are deleted.

When cvd create `--daemon=false` runs, the monitor view can open the log
files from the previous run. The newly running device deletes the old
log files and starts writing new ones, but the monitor holds references
to the old files, and waits forever for them to update.

This change adds delete event monitoring to the inotify watches, and
reads through through the inotify event list to scan for delete events.
Delete events trigger resetting the monitor view state so it can re-open
the log files and create new watches.

Bug: b/526626064
Test: launch device, exit, launch new device

Author: Databean

base/cvd/cuttlefish/host/commands/cvd/cli/commands/monitor/monitor.cc

@@ -54,7 +54,7 @@ void UpdateFileAndWatch(const SharedFD& inotify_fd, const std::string& path,
     }
   }
   if (fd->IsOpen() && watch == -1) {
-    watch = inotify_fd->InotifyAddWatch(path, IN_MODIFY);
+    watch = inotify_fd->InotifyAddWatch(path, IN_DELETE_SELF | IN_MODIFY);
   }
 }
 
@@ -95,7 +95,8 @@ Result<void> MonitorLogs(const LocalInstance& instance, SharedFD stop_eventfd) {
 
   const std::string logs_dir =
       absl::StrCat(instance.InstanceDirectory(), "/logs");
-  const int dir_watch = inotify_fd->InotifyAddWatch(logs_dir, IN_CREATE);
+  const int dir_watch =
+      inotify_fd->InotifyAddWatch(logs_dir, IN_CREATE | IN_DELETE);
 
   int kernel_watch = -1;
   int launcher_watch = -1;
@@ -112,16 +113,17 @@ Result<void> MonitorLogs(const LocalInstance& instance, SharedFD stop_eventfd) {
         }
         launcher_fd = SharedFD::Open(launcher_log, O_RDONLY);
         if (launcher_fd->IsOpen()) {
-          launcher_watch = inotify_fd->InotifyAddWatch(launcher_log, IN_MODIFY);
+          launcher_watch = inotify_fd->InotifyAddWatch(
+              launcher_log, IN_DELETE_SELF | IN_MODIFY);
           using_assemble_log = false;
         }
       } else if (!launcher_fd->IsOpen()) {
         if (FileExists(assemble_log)) {
           launcher_fd = SharedFD::Open(assemble_log, O_RDONLY);
           if (launcher_fd->IsOpen()) {
             if (launcher_watch == -1) {
-              launcher_watch =
-                  inotify_fd->InotifyAddWatch(assemble_log, IN_MODIFY);
+              launcher_watch = inotify_fd->InotifyAddWatch(
+                  assemble_log, IN_DELETE_SELF | IN_MODIFY);
             }
           }
         }
@@ -212,6 +214,29 @@ Result<void> MonitorLogs(const LocalInstance& instance, SharedFD stop_eventfd) {
           __attribute__((aligned(__alignof__(struct inotify_event))));
       ssize_t read_res = 0;
       while ((read_res = inotify_fd->Read(buf, sizeof(buf))) > 0) {
+        char* ptr = buf;
+        while (ptr < buf + read_res) {
+          inotify_event* event = reinterpret_cast<inotify_event*>(ptr);
+          if (event->mask & (IN_DELETE | IN_DELETE_SELF | IN_IGNORED)) {
+            using_assemble_log = true;
+            if (launcher_watch != -1) {
+              inotify_fd->InotifyRmWatch(launcher_watch);
+              launcher_watch = -1;
+            }
+            launcher_fd = SharedFD();
+            if (kernel_watch != -1) {
+              inotify_fd->InotifyRmWatch(kernel_watch);
+              kernel_watch = -1;
+            }
+            kernel_fd = SharedFD();
+            if (logcat_watch != -1) {
+              inotify_fd->InotifyRmWatch(logcat_watch);
+              logcat_watch = -1;
+            }
+            logcat_fd = SharedFD();
+          }
+          ptr += sizeof(inotify_event) + event->len;
+        }
       }
       CF_EXPECT(read_res != 0,
                 "Unexpected End-of-File reading inotify descriptor");