Re: [PATCH] eventfs: Create dentries and inodes at dir open

@@ -19,6 +19,7 @@
 #include <linux/namei.h>
 #include <linux/workqueue.h>
 #include <linux/security.h>
+#include <linux/siphash.h>
 #include <linux/tracefs.h>
 #include <linux/kref.h>
 #include <linux/delay.h>

@@ -32,6 +33,9 @@
  */
 static DEFINE_MUTEX(eventfs_mutex);
 
+/* Used for making inode numbers */
+static siphash_key_t inode_key;
+
 /*
  * The eventfs_inode (ei) itself is protected by SRCU. It is released from
  * its parent's list and will have is_freed set (under eventfs_mutex).

@@ -57,6 +61,28 @@ static int eventfs_dir_open(struct inode *inode, struct file *file);
 static int eventfs_iterate(struct file *file, struct dir_context *ctx);
 static int eventfs_dir_release(struct inode *inode, struct file *file);
 
+/* Copied from scripts/kconfig/symbol.c */
+static unsigned strhash(const char *s)
+{
+	/* fnv32 hash */
+	unsigned hash = 2166136261U;
+	for (; *s; s++)
+		hash = (hash ^ *s) * 0x01000193;
+	return hash;
+}
+
+/* Just try to make something consistent and unique */
+static int eventfs_inode_ino(struct eventfs_inode *ei, const char *name)
+{
+	unsigned long sip = (unsigned long)ei;
+
+	sip += strhash(name);
+	sip = siphash_1u32((int)sip, &inode_key);
+
+	/* keep it positive */
+	return sip & ((1U << 31) - 1);
+}
+
 static void update_attr(struct eventfs_attr *attr, struct iattr *iattr)
 {
 	unsigned int ia_valid = iattr->ia_valid;

@@ -491,6 +517,8 @@ create_file_dentry(struct eventfs_inode *ei, int idx,
 	mutex_unlock(&eventfs_mutex);
 
 	dentry = create_file(name, mode, attr, parent, data, fops);
+	if (!IS_ERR_OR_NULL(dentry))
+		dentry->d_inode->i_ino = eventfs_inode_ino(ei, name);
 
 	mutex_lock(&eventfs_mutex);
 

@@ -585,6 +613,8 @@ create_dir_dentry(struct eventfs_inode *pei, struct eventfs_inode *ei,
 	mutex_unlock(&eventfs_mutex);
 
 	dentry = create_dir(ei, parent);
+	if (!IS_ERR_OR_NULL(dentry))
+		dentry->d_inode->i_ino = eventfs_inode_ino(ei, ei->name);
 
 	mutex_lock(&eventfs_mutex);
 

@@ -721,19 +751,19 @@ struct eventfs_list {
 	int			count;
 };
 
-static int update_entry(struct eventfs_dents *dents, struct dentry *d,
-		     int type, int cnt)
+static int update_entry(struct eventfs_dents *dents, struct eventfs_inode *ei,
+			const char *name, int type, int cnt)
 {
-	dents[cnt].name = kstrdup_const(d->d_name.name, GFP_KERNEL);
+	dents[cnt].name = kstrdup_const(name, GFP_KERNEL);
 	if (!dents[cnt].name)
 		return -ENOMEM;
-	dents[cnt].ino = d->d_inode->i_ino;
+	dents[cnt].ino = eventfs_inode_ino(ei, name);
 	dents[cnt].type = type;
 	return 0;
 }
 
-static int add_entry(struct eventfs_dents **edents, struct dentry *d,
-		     int type, int cnt)
+static int add_entry(struct eventfs_dents **edents, struct eventfs_inode *ei,
+		     const char *name, int type, int cnt)
 {
 	struct eventfs_dents *tmp;
 

@@ -742,7 +772,7 @@ static int add_entry(struct eventfs_dents **edents, struct dentry *d,
 		return -ENOMEM;
 	*edents = tmp;
 
-	return update_entry(tmp, d, type, cnt);
+	return update_entry(tmp, ei, name, type, cnt);
 }
 
 /*

@@ -758,8 +788,6 @@ static int eventfs_dir_open(struct inode *inode, struct file *file)
 	struct tracefs_inode *ti;
 	struct eventfs_inode *ei;
 	struct eventfs_dents *dents;
-	struct dentry *ei_dentry = NULL;
-	struct dentry *dentry;
 	const char *name;
 	umode_t mode;
 	void *data;

@@ -780,11 +808,11 @@ static int eventfs_dir_open(struct inode *inode, struct file *file)
 
 	mutex_lock(&eventfs_mutex);
 	ei = READ_ONCE(ti->private);
-	if (ei && !ei->is_freed)
-		ei_dentry = READ_ONCE(ei->dentry);
+	if (ei && ei->is_freed)
+		ei = NULL;
 	mutex_unlock(&eventfs_mutex);
 
-	if (!ei_dentry) {
+	if (!ei) {
 		srcu_read_unlock(&eventfs_srcu, idx);
 		return -ENOENT;
 	}

@@ -810,7 +838,6 @@ static int eventfs_dir_open(struct inode *inode, struct file *file)
 		return -ENOMEM;
 	}
 
-	inode_lock(ei_dentry->d_inode);
 	for (i = 0; i < ei->nr_entries; i++) {
 		void *cdata = data;
 		entry = &ei->entries[i];

@@ -830,12 +857,7 @@ static int eventfs_dir_open(struct inode *inode, struct file *file)
 		/* callbacks returning zero just means skip this file */
 		if (r == 0)
 			continue;
-		dentry = create_file_dentry(ei, i, ei_dentry, name, mode, cdata, fops);
-		if (!dentry)
-			continue;
-
-		ret = update_entry(dents, dentry, DT_REG, cnt);
-		dput(dentry);
+		ret = update_entry(dents, ei, name, DT_REG, cnt);
 
 		if (ret < 0)
 		    goto fail;

@@ -845,12 +867,7 @@ static int eventfs_dir_open(struct inode *inode, struct file *file)
 
 	list_for_each_entry_srcu(ei_child, &ei->children, list,
 				 srcu_read_lock_held(&eventfs_srcu)) {
-		dentry = create_dir_dentry(ei, ei_child, ei_dentry);
-		if (!dentry)
-			continue;
-
-		ret = add_entry(&dents, dentry, DT_DIR, cnt);
-		dput(dentry);
+		ret = add_entry(&dents, ei_child, ei_child->name, DT_DIR, cnt);
 		if (ret < 0)
 			goto fail;
 		cnt++;

@@ -859,12 +876,10 @@ static int eventfs_dir_open(struct inode *inode, struct file *file)
 	edents->count = cnt;
 	edents->dents = dents;
 
-	inode_unlock(ei_dentry->d_inode);
 	srcu_read_unlock(&eventfs_srcu, idx);
 	file->private_data = edents;
 	return 0;
  fail:
-	inode_unlock(ei_dentry->d_inode);
 	srcu_read_unlock(&eventfs_srcu, idx);
 	for (; cnt >= 0; cnt--)
 		kfree_const(dents[cnt].name);

@@ -1029,6 +1044,9 @@ struct eventfs_inode *eventfs_create_events_dir(const char *name, struct dentry
 	if (IS_ERR(dentry))
 		return ERR_CAST(dentry);
 
+	if (siphash_key_is_zero(&inode_key))
+		get_random_bytes(&inode_key, sizeof(inode_key));
+
 	ei = kzalloc(sizeof(*ei), GFP_KERNEL);
 	if (!ei)
 		goto fail_ei;