[PATCH v2 2/2] fanotify: support reporting thread id instead of process id

[Amir Goldstein <amir73il@xxxxxxxxx>]

From: nixiaoming <nixiaoming@xxxxxxxxxx>

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

Signed-off-by: nixiaoming <nixiaoming@xxxxxxxxxx>
Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
---
 fs/notify/fanotify/fanotify.c      | 9 ++++++---
 fs/notify/fanotify/fanotify.h      | 2 +-
 fs/notify/fanotify/fanotify_user.c | 2 +-
 include/uapi/linux/fanotify.h      | 9 +++++++--
 4 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index 94b52157bf8d..e380027e545c 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -25,7 +25,7 @@ static bool should_merge(struct fsnotify_event *old_fsn,
 	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;
@@ -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 (FAN_GROUP_FLAG(group, FAN_EVENT_INFO_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);
@@ -268,7 +271,7 @@ static void fanotify_free_event(struct fsnotify_event *fsn_event)
 
 	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));
diff --git a/fs/notify/fanotify/fanotify.h b/fs/notify/fanotify/fanotify.h
index 8609ba06f474..d8d85104e7ff 100644
--- a/fs/notify/fanotify/fanotify.h
+++ b/fs/notify/fanotify/fanotify.h
@@ -19,7 +19,7 @@ struct fanotify_event_info {
 	 * during this object's lifetime
 	 */
 	struct path path;
-	struct pid *tgid;
+	struct pid *pid;
 };
 
 /*
diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
index 15719d4aa4b5..039d31ea4380 100644
--- a/fs/notify/fanotify/fanotify_user.c
+++ b/fs/notify/fanotify/fanotify_user.c
@@ -132,7 +132,7 @@ static int fill_event_metadata(struct fsnotify_group *group,
 	metadata->vers = FANOTIFY_METADATA_VERSION;
 	metadata->reserved = 0;
 	metadata->mask = fsn_event->mask & FAN_ALL_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 {
diff --git a/include/uapi/linux/fanotify.h b/include/uapi/linux/fanotify.h
index ad81234d1919..6d98d14a6314 100644
--- a/include/uapi/linux/fanotify.h
+++ b/include/uapi/linux/fanotify.h
@@ -38,9 +38,14 @@
 #define FAN_UNLIMITED_MARKS	0x00000020
 #define FAN_ENABLE_AUDIT	0x00000040
 
+/* Flags to determine fanotify event format */
+#define FAN_EVENT_INFO_TID	0x00000100	/* event->pid is thread id */
+
+#define FAN_EVENT_INFO_FLAGS	(FAN_EVENT_INFO_TID)
+
 #define FAN_ALL_INIT_FLAGS	(FAN_CLOEXEC | FAN_NONBLOCK | \
-				 FAN_ALL_CLASS_BITS | FAN_UNLIMITED_QUEUE |\
-				 FAN_UNLIMITED_MARKS)
+				 FAN_ALL_CLASS_BITS | FAN_EVENT_INFO_FLAGS | \
+				 FAN_UNLIMITED_QUEUE | FAN_UNLIMITED_MARKS)
 
 /* flags used for fanotify_modify_mark() */
 #define FAN_MARK_ADD		0x00000001
-- 
2.17.1