[RFC PATCH 2/3] ovl: introduce struct ovl_file_entry

[Chengguang Xu <cgxu519@mykernel.net>]

Introduce new struct ovl_file_entry to store real file
and real vm_ops handler.

Signed-off-by: Chengguang Xu <cgxu519@mykernel.net>
---
 fs/overlayfs/file.c | 64 ++++++++++++++++++++++++++++++++++++++-------
 1 file changed, 54 insertions(+), 10 deletions(-)

diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c
index 0d940e29d62b..14ab5344a918 100644
--- a/fs/overlayfs/file.c
+++ b/fs/overlayfs/file.c
@@ -21,6 +21,39 @@ struct ovl_aio_req {
 	struct fd fd;
 };
 
+struct ovl_file_entry {
+	struct file *realfile;
+	void *vm_ops;
+};
+
+struct file *ovl_get_realfile(struct file *file)
+{
+	struct ovl_file_entry *ofe = file->private_data;
+
+	return ofe->realfile;
+}
+
+void ovl_set_realfile(struct file *file, struct file *realfile)
+{
+	struct ovl_file_entry *ofe = file->private_data;
+
+	ofe->realfile = realfile;
+}
+
+void *ovl_get_real_vmops(struct file *file)
+{
+	struct ovl_file_entry *ofe = file->private_data;
+
+	return ofe->vm_ops;
+}
+
+void ovl_set_real_vmops(struct file *file, void *vm_ops)
+{
+	struct ovl_file_entry *ofe = file->private_data;
+
+	ofe->vm_ops = vm_ops;
+}
+
 static struct kmem_cache *ovl_aio_request_cachep;
 
 static char ovl_whatisit(struct inode *inode, struct inode *realinode)
@@ -105,14 +138,14 @@ static int ovl_change_flags(struct file *file, unsigned int flags)
 	return 0;
 }
 
-static int ovl_real_fdget_meta(const struct file *file, struct fd *real,
+static int ovl_real_fdget_meta(struct file *file, struct fd *real,
 			       bool allow_meta)
 {
 	struct inode *inode = file_inode(file);
 	struct inode *realinode;
 
 	real->flags = 0;
-	real->file = file->private_data;
+	real->file = ovl_get_realfile(file);
 
 	if (allow_meta)
 		realinode = ovl_inode_real(inode);
@@ -134,7 +167,7 @@ static int ovl_real_fdget_meta(const struct file *file, struct fd *real,
 	return 0;
 }
 
-static int ovl_real_fdget(const struct file *file, struct fd *real)
+static int ovl_real_fdget(struct file *file, struct fd *real)
 {
 	return ovl_real_fdget_meta(file, real, false);
 }
@@ -144,25 +177,36 @@ static int ovl_open(struct inode *inode, struct file *file)
 	struct file *realfile;
 	int err;
 
+	file->private_data = kzalloc(sizeof(struct ovl_file_entry), GFP_KERNEL);
+	if (!file->private_data)
+		return -ENOMEM;
+
 	err = ovl_maybe_copy_up(file_dentry(file), file->f_flags);
 	if (err)
-		return err;
+		goto out;
 
 	/* No longer need these flags, so don't pass them on to underlying fs */
 	file->f_flags &= ~(O_CREAT | O_EXCL | O_NOCTTY | O_TRUNC);
 
 	realfile = ovl_open_realfile(file, ovl_inode_realdata(inode));
-	if (IS_ERR(realfile))
-		return PTR_ERR(realfile);
-
-	file->private_data = realfile;
+	if (IS_ERR(realfile)) {
+		err = PTR_ERR(realfile);
+		goto out;
+	}
 
+	ovl_set_realfile(file, realfile);
 	return 0;
+out:
+	kfree(file->private_data);
+	file->private_data = NULL;
+	return err;
 }
 
 static int ovl_release(struct inode *inode, struct file *file)
 {
-	fput(file->private_data);
+	fput(ovl_get_realfile(file));
+	kfree(file->private_data);
+	file->private_data = NULL;
 
 	return 0;
 }
@@ -451,7 +495,7 @@ static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 
 static int ovl_mmap(struct file *file, struct vm_area_struct *vma)
 {
-	struct file *realfile = file->private_data;
+	struct file *realfile = ovl_get_realfile(file);
 	const struct cred *old_cred;
 	int ret;
 
-- 
2.20.1