fanotify: support reporting thread id instead of process id

In order to identify which thread triggered the event in a
multi-threaded program, add the FAN_REPORT_TID flag in fanotify_init to
opt-in for reporting the event creator's thread id information.

Signed-off-by: nixiaoming <[e-mail]>
Signed-off-by: Amir Goldstein <[e-mail]>
Signed-off-by: Jan Kara <[e-mail]>

fs/notify/fanotify/fanotify.c

···
 	old = FANOTIFY_E(old_fsn);
 	new = FANOTIFY_E(new_fsn);
 
-	if (old_fsn->inode == new_fsn->inode && old->tgid == new->tgid &&
+	if (old_fsn->inode == new_fsn->inode && old->pid == new->pid &&
 	    old->path.mnt == new->path.mnt &&
 	    old->path.dentry == new->path.dentry)
 		return true;
···
 		goto out;
 init: __maybe_unused
 	fsnotify_init_event(&event->fse, inode, mask);
-	event->tgid = get_pid(task_tgid(current));
+	if (FAN_GROUP_FLAG(group, FAN_REPORT_TID))
+		event->pid = get_pid(task_pid(current));
+	else
+		event->pid = get_pid(task_tgid(current));
 	if (path) {
 		event->path = *path;
 		path_get(&event->path);
···
 
 	event = FANOTIFY_E(fsn_event);
 	path_put(&event->path);
-	put_pid(event->tgid);
+	put_pid(event->pid);
 	if (fanotify_is_perm_event(fsn_event->mask)) {
 		kmem_cache_free(fanotify_perm_event_cachep,
 				FANOTIFY_PE(fsn_event));

fs/notify/fanotify/fanotify.h

···
 	 * during this object's lifetime
 	 */
 	struct path path;
-	struct pid *tgid;
+	struct pid *pid;
 };
 
 /*

fs/notify/fanotify/fanotify_user.c

···
 	metadata->vers = FANOTIFY_METADATA_VERSION;
 	metadata->reserved = 0;
 	metadata->mask = fsn_event->mask & FANOTIFY_OUTGOING_EVENTS;
-	metadata->pid = pid_vnr(event->tgid);
+	metadata->pid = pid_vnr(event->pid);
 	if (unlikely(fsn_event->mask & FAN_Q_OVERFLOW))
 		metadata->fd = FAN_NOFD;
 	else {
···
  */
 static int __init fanotify_user_setup(void)
 {
-	BUILD_BUG_ON(HWEIGHT32(FANOTIFY_INIT_FLAGS) != 6);
+	BUILD_BUG_ON(HWEIGHT32(FANOTIFY_INIT_FLAGS) != 7);
 	BUILD_BUG_ON(HWEIGHT32(FANOTIFY_MARK_FLAGS) != 9);
 
 	fanotify_mark_cache = KMEM_CACHE(fsnotify_mark,

include/linux/fanotify.h

···
 				 FAN_CLASS_PRE_CONTENT)
 
 #define FANOTIFY_INIT_FLAGS	(FANOTIFY_CLASS_BITS | \
+				 FAN_REPORT_TID | \
 				 FAN_CLOEXEC | FAN_NONBLOCK | \
 				 FAN_UNLIMITED_QUEUE | FAN_UNLIMITED_MARKS)
 

include/uapi/linux/fanotify.h

···
 #define FAN_UNLIMITED_MARKS	0x00000020
 #define FAN_ENABLE_AUDIT	0x00000040
 
+/* Flags to determine fanotify event format */
+#define FAN_REPORT_TID		0x00000100	/* event->pid is thread id */
+
 /* Deprecated - do not use this in programs and do not add new flags here! */
 #define FAN_ALL_INIT_FLAGS	(FAN_CLOEXEC | FAN_NONBLOCK | \
 				 FAN_ALL_CLASS_BITS | FAN_UNLIMITED_QUEUE |\