[PATCH 30/35] union-mount: Implement union-aware writable open()

[Valerie Aurora <vaurora@redhat.com>]

Copy up a file when opened with write permissions.  Does not copy up
the file data when O_TRUNC is specified.
---
 fs/namei.c |   28 ++++++++++++++++++++++++++++
 1 files changed, 28 insertions(+), 0 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index a6f7d5d..85a5451 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1929,6 +1929,24 @@ exit:
 	return ERR_PTR(error);
 }
 
+static int open_union_copyup(struct nameidata *nd, struct path *path,
+			     int open_flag)
+{
+	struct vfsmount *oldmnt = path->mnt;
+	int error;
+
+	if (open_flag & O_TRUNC)
+		error = union_copyup_len(nd, path, 0);
+	else
+		error = union_copyup(nd, path);
+	if (error)
+		return error;
+	if (oldmnt != path->mnt)
+		mntput(nd->path.mnt);
+
+	return error;
+}
+
 static struct file *do_last(struct nameidata *nd, struct path *path,
 			    int open_flag, int acc_mode,
 			    int mode, const char *pathname,
@@ -1979,6 +1997,11 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
 		error = -ENOTDIR;
 		if (*want_dir && !path->dentry->d_inode->i_op->lookup)
 			goto exit_dput;
+		if (acc_mode & MAY_WRITE) {
+			error = open_union_copyup(nd, path, open_flag);
+			if (error)
+				goto exit_dput;
+		}
 		path_to_nameidata(path, nd);
 		audit_inode(pathname, nd->path.dentry);
 		goto ok;
@@ -2050,6 +2073,11 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
 	if (path->dentry->d_inode->i_op->follow_link)
 		return NULL;
 
+	if (acc_mode & MAY_WRITE) {
+		error = open_union_copyup(nd, path, open_flag);
+		if (error)
+			goto exit_dput;
+	}
 	path_to_nameidata(path, nd);
 	error = -EISDIR;
 	if (S_ISDIR(path->dentry->d_inode->i_mode))
-- 
1.6.3.3