[PATCH v2] fanotify reports the thread id of the event trigger

[nixiaoming]

In order to identify which thread triggered the event in the
multi-threaded program, add the FAN_EVENT_INFO_TID tag in fanotify_init
to select whether to report the event creator's thread id information.

Signed-off-by: nixiaoming <nixiaoming@xxxxxxxxxx>
---
 fs/notify/fanotify/fanotify.c      | 5 ++++-
 fs/notify/fanotify/fanotify_user.c | 5 +++--
 include/linux/fsnotify_backend.h   | 1 +
 include/uapi/linux/fanotify.h      | 1 +
 4 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 94b5215..5a3af87 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -171,7 +171,10 @@ struct fanotify_event_info *fanotify_alloc_event(struct fsnotify_group *group,
 		goto out;
 init: __maybe_unused
 	fsnotify_init_event(&event->fse, inode, mask);
-	event->tgid = get_pid(task_tgid(current));
+	if (group->fanotify_data.should_report_tid)
+		event->tgid = get_pid(task_pid(current));
+	else
+		event->tgid = get_pid(task_tgid(current));
 	if (path) {
 		event->path = *path;
 		path_get(&event->path);
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 6905488..3aa425b 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -693,9 +693,9 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
 		return -EPERM;
 
 #ifdef CONFIG_AUDITSYSCALL
-	if (flags & ~(FAN_ALL_INIT_FLAGS | FAN_ENABLE_AUDIT))
+	if (flags & ~(FAN_ALL_INIT_FLAGS | FAN_ENABLE_AUDIT | FAN_EVENT_INFO_TID))
 #else
-	if (flags & ~FAN_ALL_INIT_FLAGS)
+	if (flags & ~(FAN_ALL_INIT_FLAGS | FAN_EVENT_INFO_TID))
 #endif
 		return -EINVAL;
 
@@ -731,6 +731,7 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags)
 	}
 
 	group->fanotify_data.user = user;
+	group->fanotify_data.should_report_tid = (flags & FAN_EVENT_INFO_TID) ? true : false;
 	atomic_inc(&user->fanotify_listeners);
 	group->memcg = get_mem_cgroup_from_mm(current->mm);
 
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index b8f4182..44c659f 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -193,6 +193,7 @@ struct fsnotify_group {
 			unsigned int max_marks;
 			struct user_struct *user;
 			bool audit;
+			bool should_report_tid;
 		} fanotify_data;
 #endif /* CONFIG_FANOTIFY */
 	};
diff --git a/include/uapi/linux/fanotify.h b/include/uapi/linux/fanotify.h
index 7424791..4eba41c 100644
--- a/include/uapi/linux/fanotify.h
+++ b/include/uapi/linux/fanotify.h
@@ -18,6 +18,7 @@
 
 #define FAN_ONDIR		0x40000000	/* event occurred against dir */
 
+#define FAN_EVENT_INFO_TID	0x02000000	/* reports the thread id of the event trigger */
 #define FAN_EVENT_ON_CHILD	0x08000000	/* interested in child events */
 
 /* helper events */
-- 
2.10.1