[PATCH 3/6] eventfs: Remove fsnotify*() functions from lookup()

[PATCH 3/6] eventfs: Remove fsnotify*() functions from lookup()

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

The dentries and inodes are created when referenced in the lookup code.
There's no reason to call fsnotify_*() functions when they are created by
a reference. It doesn't make any sense.

Link: https://lore.kernel.org/linux-trace-kernel/20240201002719.GS2087318@ZenIV/

Cc: stable@vger.kernel.org
Fixes: a376007917776 ("eventfs: Implement functions to create files and dirs when accessed");
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 fs/tracefs/event_inode.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index ca7daee7c811..9e031e5a2713 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -366,7 +366,6 @@ static struct dentry *lookup_file(struct eventfs_inode *parent_ei,
 	dentry->d_fsdata = get_ei(parent_ei);
 
 	d_add(dentry, inode);
-	fsnotify_create(dentry->d_parent->d_inode, dentry);
 	return NULL;
 };
 
@@ -408,7 +407,6 @@ static struct dentry *lookup_dir_entry(struct dentry *dentry,
 	inc_nlink(inode);
 	d_add(dentry, inode);
 	inc_nlink(dentry->d_parent->d_inode);
-	fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
 	return NULL;
 }
 
-- 
2.43.0

[PATCH 4/6] eventfs: Keep all directory links at 1

[Steven Rostedt]

From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

The directory link count in eventfs was somewhat bogus. It was only being
updated when a directory child was being looked up and not on creation.

One solution would be to update in get_attr() the link count by iterating
the ei->children list and then adding 2. But that could slow down simple
stat() calls, especially if it's done on all directories in eventfs.

Another solution would be to add a parent pointer to the eventfs_inode
and keep track of the number of sub directories it has on creation. But
this adds overhead for something not really worthwhile.

The solution decided upon is to keep all directory links in eventfs as 1.
This tells user space not to rely on the hard links of directories. Which
in this case it shouldn't.

Link: https://lore.kernel.org/linux-trace-kernel/20240201002719.GS2087318@ZenIV/

Cc: stable@vger.kernel.org
Fixes: c1504e510238 ("eventfs: Implement eventfs dir creation functions")
Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 fs/tracefs/event_inode.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index 9e031e5a2713..110e8a272189 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c
@@ -404,9 +404,7 @@ static struct dentry *lookup_dir_entry(struct dentry *dentry,
 
 	dentry->d_fsdata = get_ei(ei);
 
-	inc_nlink(inode);
 	d_add(dentry, inode);
-	inc_nlink(dentry->d_parent->d_inode);
 	return NULL;
 }
 
@@ -769,9 +767,17 @@ struct eventfs_inode *eventfs_create_events_dir(const char *name, struct dentry
 
 	dentry->d_fsdata = get_ei(ei);
 
-	/* directory inodes start off with i_nlink == 2 (for "." entry) */
-	inc_nlink(inode);
+	/*
+	 * Keep all eventfs directories with i_nlink == 1.
+	 * Due to the dynamic nature of the dentry creations and not
+	 * wanting to add a pointer to the parent eventfs_inode in the
+	 * eventfs_inode structure, keeping the i_nlink in sync with the
+	 * number of directories would cause too much complexity for
+	 * something not worth much. Keeping directory links at 1
+	 * tells userspace not to trust the link number.
+	 */
 	d_instantiate(dentry, inode);
+	/* The dentry of the "events" parent does keep track though */
 	inc_nlink(dentry->d_parent->d_inode);
 	fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
 	tracefs_end_creating(dentry);
-- 
2.43.0