Re: [PATCH v2 03/17] ovl: decode pure upper file handles

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On Fri, Jan 19, 2018 at 02:23:35AM +0200, Amir Goldstein wrote:
> > How is this for an option?
[...]
> > +struct dentry *d_obtain_alias_fsdata(struct inode *inode, void **fsdata)
> > +{
> > +       return __d_obtain_alias(inode, 1, fsdata);
> >  }
> >  EXPORT_SYMBOL(d_obtain_alias);

It would work, but I like this interface better:

+extern struct dentry * d_alloc_anon(struct super_block *);
+extern struct dentry * d_instantiate_anon(struct dentry *, struct inode *);

And full patch:

diff --git a/fs/dcache.c b/fs/dcache.c
index b5d5ea984ac4..15dc32178813 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1699,9 +1699,15 @@ struct dentry *d_alloc(struct dentry * parent, const struct qstr *name)
 }
 EXPORT_SYMBOL(d_alloc);
 
+struct dentry *d_alloc_anon(struct super_block *sb)
+{
+	return __d_alloc(sb, NULL);
+}
+EXPORT_SYMBOL(d_alloc_anon);
+
 struct dentry *d_alloc_cursor(struct dentry * parent)
 {
-	struct dentry *dentry = __d_alloc(parent->d_sb, NULL);
+	struct dentry *dentry = d_alloc_anon(parent->d_sb);
 	if (dentry) {
 		dentry->d_flags |= DCACHE_RCUACCESS | DCACHE_DENTRY_CURSOR;
 		dentry->d_parent = dget(parent);
@@ -1887,7 +1893,7 @@ struct dentry *d_make_root(struct inode *root_inode)
 	struct dentry *res = NULL;
 
 	if (root_inode) {
-		res = __d_alloc(root_inode->i_sb, NULL);
+		res = d_alloc_anon(root_inode->i_sb);
 		if (res)
 			d_instantiate(res, root_inode);
 		else
@@ -1926,33 +1932,18 @@ struct dentry *d_find_any_alias(struct inode *inode)
 }
 EXPORT_SYMBOL(d_find_any_alias);
 
-static struct dentry *__d_obtain_alias(struct inode *inode, int disconnected)
+static struct dentry *__d_instantiate_anon(struct dentry *dentry,
+					   struct inode *inode,
+					   bool disconnected)
 {
-	struct dentry *tmp;
 	struct dentry *res;
-	unsigned add_flags;
-
-	if (!inode)
-		return ERR_PTR(-ESTALE);
-	if (IS_ERR(inode))
-		return ERR_CAST(inode);
-
-	res = d_find_any_alias(inode);
-	if (res)
-		goto out_iput;
 
-	tmp = __d_alloc(inode->i_sb, NULL);
-	if (!tmp) {
-		res = ERR_PTR(-ENOMEM);
-		goto out_iput;
-	}
-
-	security_d_instantiate(tmp, inode);
+	security_d_instantiate(dentry, inode);
 	spin_lock(&inode->i_lock);
 	res = __d_find_any_alias(inode);
 	if (res) {
 		spin_unlock(&inode->i_lock);
-		dput(tmp);
+		dput(dentry);
 		goto out_iput;
 	}
 
@@ -1962,22 +1953,56 @@ static struct dentry *__d_obtain_alias(struct inode *inode, int disconnected)
 	if (disconnected)
 		add_flags |= DCACHE_DISCONNECTED;
 
-	spin_lock(&tmp->d_lock);
-	__d_set_inode_and_type(tmp, inode, add_flags);
-	hlist_add_head(&tmp->d_u.d_alias, &inode->i_dentry);
-	hlist_bl_lock(&tmp->d_sb->s_anon);
-	hlist_bl_add_head(&tmp->d_hash, &tmp->d_sb->s_anon);
-	hlist_bl_unlock(&tmp->d_sb->s_anon);
-	spin_unlock(&tmp->d_lock);
+	spin_lock(&dentry->d_lock);
+	__d_set_inode_and_type(dentry, inode, add_flags);
+	hlist_add_head(&dentry->d_u.d_alias, &inode->i_dentry);
+	hlist_bl_lock(&dentry->d_sb->s_anon);
+	hlist_bl_add_head(&dentry->d_hash, &dentry->d_sb->s_anon);
+	hlist_bl_unlock(&dentry->d_sb->s_anon);
+	spin_unlock(&dentry->d_lock);
 	spin_unlock(&inode->i_lock);
 
-	return tmp;
+	return dentry;
 
  out_iput:
 	iput(inode);
 	return res;
 }
 
+struct dentry *d_instantiate_anon(struct dentry *dentry, struct inode *inode)
+{
+	return __d_instantiate_anon(dentry, inode, true);
+}
+EXPORT_SYMBOL(d_instantiate_anon);
+
+static struct dentry *__d_obtain_alias(struct inode *inode, bool disconnected)
+{
+	struct dentry *tmp;
+	struct dentry *res;
+	unsigned add_flags;
+
+	if (!inode)
+		return ERR_PTR(-ESTALE);
+	if (IS_ERR(inode))
+		return ERR_CAST(inode);
+
+	res = d_find_any_alias(inode);
+	if (res)
+		goto out_iput;
+
+	tmp = d_alloc_anon(inode->i_sb);
+	if (!tmp) {
+		res = ERR_PTR(-ENOMEM);
+		goto out_iput;
+	}
+
+	return __d_instantiate_anon(tmp, inode, disconnected);
+
+out_iput:
+	iput(inode);
+	return res;
+}
+
 /**
  * d_obtain_alias - find or allocate a DISCONNECTED dentry for a given inode
  * @inode: inode to allocate the dentry for
@@ -1998,7 +2023,7 @@ static struct dentry *__d_obtain_alias(struct inode *inode, int disconnected)
  */
 struct dentry *d_obtain_alias(struct inode *inode)
 {
-	return __d_obtain_alias(inode, 1);
+	return __d_obtain_alias(inode, true);
 }
 EXPORT_SYMBOL(d_obtain_alias);
 
@@ -2019,7 +2044,7 @@ EXPORT_SYMBOL(d_obtain_alias);
  */
 struct dentry *d_obtain_root(struct inode *inode)
 {
-	return __d_obtain_alias(inode, 0);
+	return __d_obtain_alias(inode, false);
 }
 EXPORT_SYMBOL(d_obtain_root);
 
diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
index 25461781c103..7477f28cb99b 100644
--- a/fs/overlayfs/export.c
+++ b/fs/overlayfs/export.c
@@ -184,28 +184,32 @@ static struct dentry *ovl_obtain_alias(struct super_block *sb,
 		return ERR_CAST(inode);
 	}
 
-	dentry = d_obtain_alias(inode);
-	if (IS_ERR(dentry) || dentry->d_fsdata)
-		return dentry;
-
-	oe = ovl_alloc_entry(!!lower);
-	if (!oe) {
-		dput(dentry);
-		return ERR_PTR(-ENOMEM);
-	}
+	if (index)
+		ovl_set_flag(OVL_INDEX, inode);
 
-	dentry->d_fsdata = oe;
-	if (upper_alias)
-		ovl_dentry_set_upper_alias(dentry);
-	if (lower) {
-		oe->lowerstack->dentry = dget(lower);
-		oe->lowerstack->layer = lowerpath->layer;
+	dentry = d_find_any_alias(inode);
+	if (!dentry) {
+		dentry = d_alloc_anon(inode->i_sb);
+		if (!dentry)
+			goto nomem;
+		oe = ovl_alloc_entry(lower ? 1 : 0);
+		if (!oe)
+			goto nomem;
+		if (lower) {
+			oe->lowerstack->dentry = dget(lower);
+			oe->lowerstack->layer = lowerpath->layer;
+		}
+		dentry->d_fsdata = oe;
+		if (upper_alias)
+			ovl_dentry_set_upper_alias(dentry);
 	}
 
-	if (index)
-		ovl_set_flag(OVL_INDEX, inode);
+	return d_instantiate_anon(dentry, inode);
 
-	return dentry;
+nomem:
+	iput(inode);
+	dput(dentry);
+	return ERR_PTR(-ENOMEM);
 }
 
 /* Get the upper or lower dentry in stach whose on layer @idx */
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 65cd8ab60b7a..82a99d366aec 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -227,6 +227,7 @@ extern seqlock_t rename_lock;
  */
 extern void d_instantiate(struct dentry *, struct inode *);
 extern struct dentry * d_instantiate_unique(struct dentry *, struct inode *);
+extern struct dentry * d_instantiate_anon(struct dentry *, struct inode *);
 extern int d_instantiate_no_diralias(struct dentry *, struct inode *);
 extern void __d_drop(struct dentry *dentry);
 extern void d_drop(struct dentry *dentry);
@@ -235,6 +236,7 @@ extern void d_set_d_op(struct dentry *dentry, const struct dentry_operations *op
 
 /* allocate/de-allocate */
 extern struct dentry * d_alloc(struct dentry *, const struct qstr *);
+extern struct dentry * d_alloc_anon(struct super_block *);
 extern struct dentry * d_alloc_pseudo(struct super_block *, const struct qstr *);
 extern struct dentry * d_alloc_parallel(struct dentry *, const struct qstr *,
 					wait_queue_head_t *);
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