[PATCH for 4.8] vfs: new d_init method

[Miklos Szeredi]

Allow filesystem to initialize dentry at allocation time.

Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxxxxx>
---
 Documentation/filesystems/Locking |  2 ++
 Documentation/filesystems/vfs.txt |  3 +++
 fs/dcache.c                       | 11 +++++++++++
 include/linux/dcache.h            |  1 +
 4 files changed, 17 insertions(+)

diff --git a/Documentation/filesystems/Locking b/Documentation/filesystems/Locking
index 75eea7ce3d7c..fbae98e01606 100644
--- a/Documentation/filesystems/Locking
+++ b/Documentation/filesystems/Locking
@@ -15,6 +15,7 @@ prototypes:
 	int (*d_compare)(const struct dentry *, const struct dentry *,
 			unsigned int, const char *, const struct qstr *);
 	int (*d_delete)(struct dentry *);
+	int (*d_init)(struct dentry *);
 	void (*d_release)(struct dentry *);
 	void (*d_iput)(struct dentry *, struct inode *);
 	char *(*d_dname)((struct dentry *dentry, char *buffer, int buflen);
@@ -28,6 +29,7 @@ d_weak_revalidate:no		no		yes	 	no
 d_hash		no		no		no		maybe
 d_compare:	yes		no		no		maybe
 d_delete:	no		yes		no		no
+d_init:	no		no		yes		no
 d_release:	no		no		yes		no
 d_prune:        no              yes             no              no
 d_iput:		no		no		yes		no
diff --git a/Documentation/filesystems/vfs.txt b/Documentation/filesystems/vfs.txt
index c61a223ef3ff..bf816aba2288 100644
--- a/Documentation/filesystems/vfs.txt
+++ b/Documentation/filesystems/vfs.txt
@@ -933,6 +933,7 @@ struct dentry_operations {
 	int (*d_compare)(const struct dentry *, const struct dentry *,
 			unsigned int, const char *, const struct qstr *);
 	int (*d_delete)(const struct dentry *);
+	int (*d_init)(struct dentry *);
 	void (*d_release)(struct dentry *);
 	void (*d_iput)(struct dentry *, struct inode *);
 	char *(*d_dname)(struct dentry *, char *, int);
@@ -1003,6 +1004,8 @@ struct dentry_operations {
 	always cache a reachable dentry. d_delete must be constant and
 	idempotent.
 
+  d_init: called when a dentry is allocated
+
   d_release: called when a dentry is really deallocated
 
   d_iput: called when a dentry loses its inode (just prior to its
diff --git a/fs/dcache.c b/fs/dcache.c
index 817c243c1ff1..9bba3e3d7c94 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1559,6 +1559,7 @@ struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
 {
 	struct dentry *dentry;
 	char *dname;
+	int err;
 
 	dentry = kmem_cache_alloc(dentry_cache, GFP_KERNEL);
 	if (!dentry)
@@ -1617,6 +1618,16 @@ struct dentry *__d_alloc(struct super_block *sb, const struct qstr *name)
 	INIT_LIST_HEAD(&dentry->d_child);
 	d_set_d_op(dentry, dentry->d_sb->s_d_op);
 
+	if (dentry->d_op && dentry->d_op->d_init) {
+		err = dentry->d_op->d_init(dentry);
+		if (err) {
+			if (dname_external(dentry))
+				kfree(external_name(dentry));
+			kmem_cache_free(dentry_cache, dentry);
+			return NULL;
+		}
+	}
+
 	this_cpu_inc(nr_dentry);
 
 	return dentry;
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index f28100f6b556..5e523c7f0d8a 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -133,6 +133,7 @@ struct dentry_operations {
 	int (*d_compare)(const struct dentry *, const struct dentry *,
 			unsigned int, const char *, const struct qstr *);
 	int (*d_delete)(const struct dentry *);
+	int (*d_init)(struct dentry *);
 	void (*d_release)(struct dentry *);
 	void (*d_prune)(struct dentry *);
 	void (*d_iput)(struct dentry *, struct inode *);
-- 
2.5.5