[PATCH 10/24] Unionfs: Inode operations

[Josef 'Jeff' Sipek]

From: Josef "Jeff" Sipek <jsipek@xxxxxxxxxxxxx>

This patch provides the inode operations for Unionfs.

Signed-off-by: Josef "Jeff" Sipek <jsipek@xxxxxxxxxxxxx>
Signed-off-by: David Quigley <dquigley@xxxxxxxxxxxxxxxxx>
Signed-off-by: Erez Zadok <ezk@xxxxxxxxxxxxx>
---
 fs/unionfs/inode.c |  939 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 939 insertions(+), 0 deletions(-)

diff --git a/fs/unionfs/inode.c b/fs/unionfs/inode.c
new file mode 100644
index 0000000..1bbef1c
--- /dev/null
+++ b/fs/unionfs/inode.c
@@ -0,0 +1,939 @@
+/*
+ * Copyright (c) 2003-2006 Erez Zadok
+ * Copyright (c) 2003-2006 Charles P. Wright
+ * Copyright (c) 2005-2006 Josef 'Jeff' Sipek
+ * Copyright (c) 2005-2006 Junjiro Okajima
+ * Copyright (c) 2005      Arun M. Krishnakumar
+ * Copyright (c) 2004-2006 David P. Quigley
+ * Copyright (c) 2003-2004 Mohammad Nayyer Zubair
+ * Copyright (c) 2003      Puja Gupta
+ * Copyright (c) 2003      Harikesavan Krishnan
+ * Copyright (c) 2003-2006 Stony Brook University
+ * Copyright (c) 2003-2006 The Research Foundation of State University of New York
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include "union.h"
+
+/* declarations added for "sparse" */
+extern struct dentry *unionfs_lookup(struct inode *, struct dentry *,
+				     struct nameidata *);
+extern int unionfs_readlink(struct dentry *dentry, char __user * buf,
+			    int bufsiz);
+extern void unionfs_put_link(struct dentry *dentry, struct nameidata *nd,
+			     void *cookie);
+
+static int unionfs_create(struct inode *parent, struct dentry *dentry,
+			  int mode, struct nameidata *nd)
+{
+	int err = 0;
+	struct dentry *hidden_dentry = NULL;
+	struct dentry *wh_dentry = NULL;
+	struct dentry *new_hidden_dentry;
+	struct dentry *hidden_parent_dentry = NULL;
+	int bindex = 0, bstart;
+	char *name = NULL;
+
+	lock_dentry(dentry);
+
+	/* We start out in the leftmost branch. */
+	bstart = dbstart(dentry);
+	hidden_dentry = unionfs_lower_dentry(dentry);
+
+	/* check if whiteout exists in this branch, i.e. lookup .wh.foo first */
+	name = alloc_whname(dentry->d_name.name, dentry->d_name.len);
+	if (IS_ERR(name)) {
+		err = PTR_ERR(name);
+		goto out;
+	}
+
+	wh_dentry = lookup_one_len(name, hidden_dentry->d_parent,
+			   dentry->d_name.len + UNIONFS_WHLEN);
+	if (IS_ERR(wh_dentry)) {
+		err = PTR_ERR(wh_dentry);
+		wh_dentry = NULL;
+		goto out;
+	}
+
+	if (wh_dentry->d_inode) {
+		/* .wh.foo has been found. */
+		/* First truncate it and then rename it to foo (hence having
+		 * the same overall effect as a normal create.
+		 */
+		struct dentry *hidden_dir_dentry;
+		struct iattr newattrs;
+
+		mutex_lock(&wh_dentry->d_inode->i_mutex);
+		newattrs.ia_valid = ATTR_CTIME | ATTR_MODE | ATTR_ATIME
+		    | ATTR_MTIME | ATTR_UID | ATTR_GID | ATTR_FORCE
+		    | ATTR_KILL_SUID | ATTR_KILL_SGID;
+
+		newattrs.ia_mode = mode & ~current->fs->umask;
+		newattrs.ia_uid = current->fsuid;
+		newattrs.ia_gid = current->fsgid;
+
+		if (wh_dentry->d_inode->i_size != 0) {
+			newattrs.ia_valid |= ATTR_SIZE;
+			newattrs.ia_size = 0;
+		}
+
+		err = notify_change(wh_dentry, &newattrs);
+
+		mutex_unlock(&wh_dentry->d_inode->i_mutex);
+
+		if (err)
+			printk(KERN_WARNING "unionfs: %s:%d: notify_change "
+				"failed: %d, ignoring..\n",
+				__FILE__, __LINE__, err);
+
+		new_hidden_dentry = unionfs_lower_dentry(dentry);
+		dget(new_hidden_dentry);
+
+		hidden_dir_dentry = dget_parent(wh_dentry);
+		lock_rename(hidden_dir_dentry, hidden_dir_dentry);
+
+		if (!(err = is_robranch_super(dentry->d_sb, bstart))) {
+			err = vfs_rename(hidden_dir_dentry->d_inode,
+					 wh_dentry,
+					 hidden_dir_dentry->d_inode,
+					 new_hidden_dentry);
+		}
+		if (!err) {
+			fsstack_copy_attr_times(parent,
+					new_hidden_dentry->d_parent->d_inode);
+			fsstack_copy_inode_size(parent,
+					new_hidden_dentry->d_parent->d_inode);
+			parent->i_nlink = unionfs_get_nlinks(parent);
+		}
+
+		unlock_rename(hidden_dir_dentry, hidden_dir_dentry);
+		dput(hidden_dir_dentry);
+
+		dput(new_hidden_dentry);
+
+		if (err) {
+			/* exit if the error returned was NOT -EROFS */
+			if (!IS_COPYUP_ERR(err))
+				goto out;
+			/* We were not able to create the file in this
+			 * branch, so, we try to create it in one branch to
+			 * left
+			 */
+			bstart--;
+		} else {
+			/* reset the unionfs dentry to point to the .wh.foo
+			 * entry.
+			 */
+
+			/* Discard any old reference. */
+			dput(unionfs_lower_dentry(dentry));
+
+			/* Trade one reference to another. */
+			unionfs_set_lower_dentry_idx(dentry, bstart, wh_dentry);
+			wh_dentry = NULL;
+
+			err = unionfs_interpose(dentry, parent->i_sb, 0);
+			goto out;
+		}
+	}
+
+	for (bindex = bstart; bindex >= 0; bindex--) {
+		hidden_dentry = unionfs_lower_dentry_idx(dentry, bindex);
+		if (!hidden_dentry) {
+			/* if hidden_dentry is NULL, create the entire
+			 * dentry directory structure in branch 'bindex'.
+			 * hidden_dentry will NOT be null when bindex == bstart
+			 * because lookup passed as a negative unionfs dentry
+			 * pointing to a lone negative underlying dentry */
+			hidden_dentry = create_parents(parent, dentry, bindex);
+			if (!hidden_dentry || IS_ERR(hidden_dentry)) {
+				if (IS_ERR(hidden_dentry))
+					err = PTR_ERR(hidden_dentry);
+				continue;
+			}
+		}
+
+		hidden_parent_dentry = lock_parent(hidden_dentry);
+		if (IS_ERR(hidden_parent_dentry)) {
+			err = PTR_ERR(hidden_parent_dentry);
+			goto out;
+		}
+		/* We shouldn't create things in a read-only branch. */
+		if (!(err = is_robranch_super(dentry->d_sb, bindex)))
+			err = vfs_create(hidden_parent_dentry->d_inode,
+					 hidden_dentry, mode, nd);
+
+		if (err || !hidden_dentry->d_inode) {
+			unlock_dir(hidden_parent_dentry);
+
+			/* break out of for loop if the error wasn't  -EROFS */
+			if (!IS_COPYUP_ERR(err))
+				break;
+		} else {
+			err = unionfs_interpose(dentry, parent->i_sb, 0);
+			if (!err) {
+				fsstack_copy_attr_times(parent,
+						hidden_parent_dentry->d_inode);
+				fsstack_copy_inode_size(parent,
+						hidden_parent_dentry->d_inode);
+				/* update number of links on parent directory */
+				parent->i_nlink = unionfs_get_nlinks(parent);
+			}
+			unlock_dir(hidden_parent_dentry);
+			break;
+		}
+	}
+
+out:
+	dput(wh_dentry);
+	kfree(name);
+
+	unlock_dentry(dentry);
+	return err;
+}
+
+struct dentry *unionfs_lookup(struct inode *parent, struct dentry *dentry,
+			      struct nameidata *nd)
+{
+	struct nameidata lowernd; /* TODO: be gentler to the stack */
+
+	if (nd)
+		memcpy(&lowernd, nd, sizeof(struct nameidata));
+	else
+		memset(&lowernd, 0, sizeof(struct nameidata));
+
+	/* The locking is done by unionfs_lookup_backend. */
+	return unionfs_lookup_backend(dentry, &lowernd, INTERPOSE_LOOKUP);
+}
+
+static int unionfs_link(struct dentry *old_dentry, struct inode *dir,
+			struct dentry *new_dentry)
+{
+	int err = 0;
+	struct dentry *hidden_old_dentry = NULL;
+	struct dentry *hidden_new_dentry = NULL;
+	struct dentry *hidden_dir_dentry = NULL;
+	struct dentry *whiteout_dentry;
+	char *name = NULL;
+
+	double_lock_dentry(new_dentry, old_dentry);
+
+	hidden_new_dentry = unionfs_lower_dentry(new_dentry);
+
+	/* check if whiteout exists in the branch of new dentry, i.e. lookup
+	 * .wh.foo first. If present, delete it
+	 */
+	name = alloc_whname(new_dentry->d_name.name, new_dentry->d_name.len);
+	if (IS_ERR(name)) {
+		err = PTR_ERR(name);
+		goto out;
+	}
+
+	whiteout_dentry = lookup_one_len(name, hidden_new_dentry->d_parent,
+				new_dentry->d_name.len + UNIONFS_WHLEN);
+	if (IS_ERR(whiteout_dentry)) {
+		err = PTR_ERR(whiteout_dentry);
+		goto out;
+	}
+
+	if (!whiteout_dentry->d_inode) {
+		dput(whiteout_dentry);
+		whiteout_dentry = NULL;
+	} else {
+		/* found a .wh.foo entry, unlink it and then call vfs_link() */
+		hidden_dir_dentry = lock_parent(whiteout_dentry);
+		err = is_robranch_super(new_dentry->d_sb, dbstart(new_dentry));
+		if (!err)
+			err = vfs_unlink(hidden_dir_dentry->d_inode,
+				       whiteout_dentry);
+
+		fsstack_copy_attr_times(dir, hidden_dir_dentry->d_inode);
+		dir->i_nlink = unionfs_get_nlinks(dir);
+		unlock_dir(hidden_dir_dentry);
+		hidden_dir_dentry = NULL;
+		dput(whiteout_dentry);
+		if (err)
+			goto out;
+	}
+
+	if (dbstart(old_dentry) != dbstart(new_dentry)) {
+		hidden_new_dentry =
+		    create_parents(dir, new_dentry, dbstart(old_dentry));
+		err = PTR_ERR(hidden_new_dentry);
+		if (IS_COPYUP_ERR(err))
+			goto docopyup;
+		if (!hidden_new_dentry || IS_ERR(hidden_new_dentry))
+			goto out;
+	}
+	hidden_new_dentry = unionfs_lower_dentry(new_dentry);
+	hidden_old_dentry = unionfs_lower_dentry(old_dentry);
+
+	BUG_ON(dbstart(old_dentry) != dbstart(new_dentry));
+	hidden_dir_dentry = lock_parent(hidden_new_dentry);
+	if (!(err = is_robranch(old_dentry)))
+		err = vfs_link(hidden_old_dentry, hidden_dir_dentry->d_inode,
+			     hidden_new_dentry);
+	unlock_dir(hidden_dir_dentry);
+
+docopyup:
+	if (IS_COPYUP_ERR(err)) {
+		int old_bstart = dbstart(old_dentry);
+		int bindex;
+
+		for (bindex = old_bstart - 1; bindex >= 0; bindex--) {
+			err =
+			    copyup_dentry(old_dentry->d_parent->
+					  d_inode, old_dentry,
+					  old_bstart, bindex, NULL,
+					  old_dentry->d_inode->i_size);
+			if (!err) {
+				hidden_new_dentry =
+				    create_parents(dir, new_dentry, bindex);
+				hidden_old_dentry = unionfs_lower_dentry(old_dentry);
+				hidden_dir_dentry =
+				    lock_parent(hidden_new_dentry);
+				/* do vfs_link */
+				err = vfs_link(hidden_old_dentry,
+					     hidden_dir_dentry->d_inode,
+					     hidden_new_dentry);
+				unlock_dir(hidden_dir_dentry);
+				goto check_link;
+			}
+		}
+		goto out;
+	}
+
+check_link:
+	if (err || !hidden_new_dentry->d_inode)
+		goto out;
+
+	/* Its a hard link, so use the same inode */
+	new_dentry->d_inode = igrab(old_dentry->d_inode);
+	d_instantiate(new_dentry, new_dentry->d_inode);
+	fsstack_copy_attr_all(dir, hidden_new_dentry->d_parent->d_inode,
+					unionfs_get_nlinks);
+	fsstack_copy_inode_size(dir, hidden_new_dentry->d_parent->d_inode);
+
+	/* propagate number of hard-links */
+	old_dentry->d_inode->i_nlink = unionfs_get_nlinks(old_dentry->d_inode);
+
+out:
+	if (!new_dentry->d_inode)
+		d_drop(new_dentry);
+
+	kfree(name);
+
+	unlock_dentry(new_dentry);
+	unlock_dentry(old_dentry);
+
+	return err;
+}
+
+static int unionfs_symlink(struct inode *dir, struct dentry *dentry,
+			   const char *symname)
+{
+	int err = 0;
+	struct dentry *hidden_dentry = NULL;
+	struct dentry *whiteout_dentry = NULL;
+	struct dentry *hidden_dir_dentry = NULL;
+	umode_t mode;
+	int bindex = 0, bstart;
+	char *name = NULL;
+
+	lock_dentry(dentry);
+
+	/* We start out in the leftmost branch. */
+	bstart = dbstart(dentry);
+
+	hidden_dentry = unionfs_lower_dentry(dentry);
+
+	/* check if whiteout exists in this branch, i.e. lookup .wh.foo
+	 * first. If present, delete it
+	 */
+	name = alloc_whname(dentry->d_name.name, dentry->d_name.len);
+	if (IS_ERR(name)) {
+		err = PTR_ERR(name);
+		goto out;
+	}
+
+	whiteout_dentry =
+	    lookup_one_len(name, hidden_dentry->d_parent,
+			   dentry->d_name.len + UNIONFS_WHLEN);
+	if (IS_ERR(whiteout_dentry)) {
+		err = PTR_ERR(whiteout_dentry);
+		goto out;
+	}
+
+	if (!whiteout_dentry->d_inode) {
+		dput(whiteout_dentry);
+		whiteout_dentry = NULL;
+	} else {
+		/* found a .wh.foo entry, unlink it and then call vfs_symlink() */
+		hidden_dir_dentry = lock_parent(whiteout_dentry);
+
+		if (!(err = is_robranch_super(dentry->d_sb, bstart)))
+			err = vfs_unlink(hidden_dir_dentry->d_inode,
+				       whiteout_dentry);
+		dput(whiteout_dentry);
+
+		fsstack_copy_attr_times(dir, hidden_dir_dentry->d_inode);
+		/* propagate number of hard-links */
+		dir->i_nlink = unionfs_get_nlinks(dir);
+
+		unlock_dir(hidden_dir_dentry);
+
+		if (err) {
+			/* exit if the error returned was NOT -EROFS */
+			if (!IS_COPYUP_ERR(err))
+				goto out;
+			/* should now try to create symlink in the another branch */
+			bstart--;
+		}
+	}
+
+	/* deleted whiteout if it was present, now do a normal vfs_symlink()
+	 * with possible recursive directory creation
+	 */
+	for (bindex = bstart; bindex >= 0; bindex--) {
+		hidden_dentry = unionfs_lower_dentry_idx(dentry, bindex);
+		if (!hidden_dentry) {
+			/* if hidden_dentry is NULL, create the entire
+			 * dentry directory structure in branch 'bindex'.
+			 * hidden_dentry will NOT be null when bindex ==
+			 * bstart because lookup passed as a negative
+			 * unionfs dentry pointing to a lone negative
+			 * underlying dentry
+			 */
+			hidden_dentry = create_parents(dir, dentry, bindex);
+			if (!hidden_dentry || IS_ERR(hidden_dentry)) {
+				if (IS_ERR(hidden_dentry))
+					err = PTR_ERR(hidden_dentry);
+
+				printk(KERN_DEBUG "hidden dentry NULL (or error)"
+					"for bindex = %d\n", bindex);
+				continue;
+			}
+		}
+
+		hidden_dir_dentry = lock_parent(hidden_dentry);
+
+		if (!(err = is_robranch_super(dentry->d_sb, bindex))) {
+			mode = S_IALLUGO;
+			err =
+			    vfs_symlink(hidden_dir_dentry->d_inode,
+					hidden_dentry, symname, mode);
+		}
+		unlock_dir(hidden_dir_dentry);
+
+		if (err || !hidden_dentry->d_inode) {
+			/* break out of for loop if error returned was NOT -EROFS */
+			if (!IS_COPYUP_ERR(err))
+				break;
+		} else {
+			err = unionfs_interpose(dentry, dir->i_sb, 0);
+			if (!err) {
+				fsstack_copy_attr_times(dir,
+						hidden_dir_dentry->d_inode);
+				fsstack_copy_inode_size(dir,
+						hidden_dir_dentry->d_inode);
+				/* update number of links on parent directory */
+				dir->i_nlink = unionfs_get_nlinks(dir);
+			}
+			break;
+		}
+	}
+
+out:
+	if (!dentry->d_inode)
+		d_drop(dentry);
+
+	kfree(name);
+	unlock_dentry(dentry);
+	return err;
+}
+
+static int unionfs_mkdir(struct inode *parent, struct dentry *dentry, int mode)
+{
+	int err = 0;
+	struct dentry *hidden_dentry = NULL, *whiteout_dentry = NULL;
+	struct dentry *hidden_parent_dentry = NULL;
+	int bindex = 0, bstart;
+	char *name = NULL;
+	int whiteout_unlinked = 0;
+	struct sioq_args args;
+
+	lock_dentry(dentry);
+	bstart = dbstart(dentry);
+
+	hidden_dentry = unionfs_lower_dentry(dentry);
+
+	/* check if whiteout exists in this branch, i.e. lookup .wh.foo first */
+	name = alloc_whname(dentry->d_name.name, dentry->d_name.len);
+	if (IS_ERR(name)) {
+		err = PTR_ERR(name);
+		goto out;
+	}
+
+	whiteout_dentry = lookup_one_len(name, hidden_dentry->d_parent,
+			   dentry->d_name.len + UNIONFS_WHLEN);
+	if (IS_ERR(whiteout_dentry)) {
+		err = PTR_ERR(whiteout_dentry);
+		goto out;
+	}
+
+	if (!whiteout_dentry->d_inode) {
+		dput(whiteout_dentry);
+		whiteout_dentry = NULL;
+	} else {
+		hidden_parent_dentry = lock_parent(whiteout_dentry);
+
+		/* found a.wh.foo entry, remove it then do vfs_mkdir */
+		if (!(err = is_robranch_super(dentry->d_sb, bstart))) {
+			args.unlink.parent = hidden_parent_dentry->d_inode;
+			args.unlink.dentry = whiteout_dentry;
+			run_sioq(__unionfs_unlink, &args);
+			err = args.err;
+		}
+		dput(whiteout_dentry);
+
+		unlock_dir(hidden_parent_dentry);
+
+		if (err) {
+			/* exit if the error returned was NOT -EROFS */
+			if (!IS_COPYUP_ERR(err))
+				goto out;
+			bstart--;
+		} else
+			whiteout_unlinked = 1;
+	}
+
+	for (bindex = bstart; bindex >= 0; bindex--) {
+		int i;
+		int bend = dbend(dentry);
+
+		if (is_robranch_super(dentry->d_sb, bindex))
+			continue;
+
+		hidden_dentry = unionfs_lower_dentry_idx(dentry, bindex);
+		if (!hidden_dentry) {
+			hidden_dentry = create_parents(parent, dentry, bindex);
+			if (!hidden_dentry || IS_ERR(hidden_dentry)) {
+				printk(KERN_DEBUG "hidden dentry NULL for "
+					"bindex = %d\n", bindex);
+				continue;
+			}
+		}
+
+		hidden_parent_dentry = lock_parent(hidden_dentry);
+
+		if (IS_ERR(hidden_parent_dentry)) {
+			err = PTR_ERR(hidden_parent_dentry);
+			goto out;
+		}
+
+		err = vfs_mkdir(hidden_parent_dentry->d_inode, hidden_dentry, mode);
+
+		unlock_dir(hidden_parent_dentry);
+
+		/* did the mkdir suceed? */
+		if (err)
+			break;
+
+		for (i = bindex + 1; i < bend; i++) {
+			if (unionfs_lower_dentry_idx(dentry, i)) {
+				dput(unionfs_lower_dentry_idx(dentry, i));
+				unionfs_set_lower_dentry_idx(dentry, i, NULL);
+			}
+		}
+		set_dbend(dentry, bindex);
+
+		err = unionfs_interpose(dentry, parent->i_sb, 0);
+		if (!err) {
+			fsstack_copy_attr_times(parent,
+					hidden_parent_dentry->d_inode);
+			fsstack_copy_inode_size(parent,
+					hidden_parent_dentry->d_inode);
+
+			/* update number of links on parent directory */
+			parent->i_nlink = unionfs_get_nlinks(parent);
+		}
+
+		err = make_dir_opaque(dentry, dbstart(dentry));
+		if (err) {
+			printk(KERN_ERR "mkdir: error creating "
+				".wh.__dir_opaque: %d\n", err);
+			goto out;
+		}
+
+		/* we are done! */
+		break;
+	}
+
+out:
+	if (!dentry->d_inode)
+		d_drop(dentry);
+
+	kfree(name);
+
+	unlock_dentry(dentry);
+	return err;
+}
+
+static int unionfs_mknod(struct inode *dir, struct dentry *dentry, int mode,
+			 dev_t dev)
+{
+	int err = 0;
+	struct dentry *hidden_dentry = NULL, *whiteout_dentry = NULL;
+	struct dentry *hidden_parent_dentry = NULL;
+	int bindex = 0, bstart;
+	char *name = NULL;
+	int whiteout_unlinked = 0;
+
+	lock_dentry(dentry);
+	bstart = dbstart(dentry);
+
+	hidden_dentry = unionfs_lower_dentry(dentry);
+
+	/* check if whiteout exists in this branch, i.e. lookup .wh.foo first */
+	name = alloc_whname(dentry->d_name.name, dentry->d_name.len);
+	if (IS_ERR(name)) {
+		err = PTR_ERR(name);
+		goto out;
+	}
+
+	whiteout_dentry = lookup_one_len(name, hidden_dentry->d_parent,
+				dentry->d_name.len + UNIONFS_WHLEN);
+	if (IS_ERR(whiteout_dentry)) {
+		err = PTR_ERR(whiteout_dentry);
+		goto out;
+	}
+
+	if (!whiteout_dentry->d_inode) {
+		dput(whiteout_dentry);
+		whiteout_dentry = NULL;
+	} else {
+		/* found .wh.foo, unlink it */
+		hidden_parent_dentry = lock_parent(whiteout_dentry);
+
+		/* found a.wh.foo entry, remove it then do vfs_mkdir */
+		if (!(err = is_robranch_super(dentry->d_sb, bstart)))
+			err = vfs_unlink(hidden_parent_dentry->d_inode,
+					 whiteout_dentry);
+		dput(whiteout_dentry);
+
+		unlock_dir(hidden_parent_dentry);
+
+		if (err) {
+			if (!IS_COPYUP_ERR(err))
+				goto out;
+
+			bstart--;
+		} else
+			whiteout_unlinked = 1;
+	}
+
+	for (bindex = bstart; bindex >= 0; bindex--) {
+		if (is_robranch_super(dentry->d_sb, bindex))
+			continue;
+
+		hidden_dentry = unionfs_lower_dentry_idx(dentry, bindex);
+		if (!hidden_dentry) {
+			hidden_dentry = create_parents(dir, dentry, bindex);
+			if (IS_ERR(hidden_dentry)) {
+				printk(KERN_DEBUG
+				       "failed to create parents on %d, err = %ld\n",
+				       bindex, PTR_ERR(hidden_dentry));
+				continue;
+			}
+		}
+
+		hidden_parent_dentry = lock_parent(hidden_dentry);
+		if (IS_ERR(hidden_parent_dentry)) {
+			err = PTR_ERR(hidden_parent_dentry);
+			goto out;
+		}
+
+		err = vfs_mknod(hidden_parent_dentry->d_inode,
+				hidden_dentry, mode, dev);
+
+		if (err) {
+			unlock_dir(hidden_parent_dentry);
+			break;
+		}
+
+		err = unionfs_interpose(dentry, dir->i_sb, 0);
+		if (!err) {
+			fsstack_copy_attr_times(dir,
+					hidden_parent_dentry->d_inode);
+			fsstack_copy_inode_size(dir,
+					hidden_parent_dentry->d_inode);
+			/* update number of links on parent directory */
+			dir->i_nlink = unionfs_get_nlinks(dir);
+		}
+		unlock_dir(hidden_parent_dentry);
+
+		break;
+	}
+
+out:
+	if (!dentry->d_inode)
+		d_drop(dentry);
+
+	kfree(name);
+
+	unlock_dentry(dentry);
+	return err;
+}
+
+int unionfs_readlink(struct dentry *dentry, char __user * buf, int bufsiz)
+{
+	int err;
+	struct dentry *hidden_dentry;
+
+	lock_dentry(dentry);
+	hidden_dentry = unionfs_lower_dentry(dentry);
+
+	if (!hidden_dentry->d_inode->i_op ||
+	    !hidden_dentry->d_inode->i_op->readlink) {
+		err = -EINVAL;
+		goto out;
+	}
+
+	err = hidden_dentry->d_inode->i_op->readlink(hidden_dentry, buf, bufsiz);
+	if (err > 0)
+		fsstack_copy_attr_atime(dentry->d_inode, hidden_dentry->d_inode);
+
+out:
+	unlock_dentry(dentry);
+	return err;
+}
+
+/* We don't lock the dentry here, because readlink does the heavy lifting. */
+static void *unionfs_follow_link(struct dentry *dentry, struct nameidata *nd)
+{
+	char *buf;
+	int len = PAGE_SIZE, err;
+	mm_segment_t old_fs;
+
+	/* This is freed by the put_link method assuming a successful call. */
+	buf = kmalloc(len, GFP_KERNEL);
+	if (!buf) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	/* read the symlink, and then we will follow it */
+	old_fs = get_fs();
+	set_fs(KERNEL_DS);
+	err = dentry->d_inode->i_op->readlink(dentry, (char __user *)buf, len);
+	set_fs(old_fs);
+	if (err < 0) {
+		kfree(buf);
+		buf = NULL;
+		goto out;
+	}
+	buf[err] = 0;
+	nd_set_link(nd, buf);
+	err = 0;
+
+out:
+	return ERR_PTR(err);
+}
+
+void unionfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
+{
+	kfree(nd_get_link(nd));
+}
+
+/* Basically copied from the kernel vfs permission(), but we've changed
+ * the following:
+ *   (1) the IS_RDONLY check is skipped, and 
+ *   (2) if you set the mount option `mode=nfsro', we assume that -EACCES
+ *   means that the export is read-only and we should check standard Unix
+ *   permissions.  This means that NFS ACL checks (or other advanced
+ *   permission features) are bypassed. Note however, that we do call
+ *   security_inode_permission, and therefore security inside SELinux, etc.
+ *   are performed.
+ */
+static int inode_permission(struct inode *inode, int mask, struct nameidata *nd,
+			    int bindex)
+{
+	int retval, submask;
+
+	if (mask & MAY_WRITE) {
+		/* The first branch is allowed to be really readonly. */
+		if (bindex == 0) {
+			umode_t mode = inode->i_mode;
+			if (IS_RDONLY(inode) &&
+			   (S_ISREG(mode) || S_ISDIR(mode) || S_ISLNK(mode)))
+				return -EROFS;
+		}
+		/*
+		 * Nobody gets write access to an immutable file.
+		 */
+		if (IS_IMMUTABLE(inode))
+			return -EACCES;
+	}
+
+	/* Ordinary permission routines do not understand MAY_APPEND. */
+	submask = mask & ~MAY_APPEND;
+	if (inode->i_op && inode->i_op->permission) {
+		retval = inode->i_op->permission(inode, submask, nd);
+		if ((retval == -EACCES) && (submask & MAY_WRITE) &&
+		    (!strcmp("nfs", (inode)->i_sb->s_type->name)) &&
+		    (nd) && (nd->mnt) && (nd->mnt->mnt_sb) &&
+		    (branchperms(nd->mnt->mnt_sb, bindex) & MAY_NFSRO)) {
+			retval = generic_permission(inode, submask, NULL);
+		}
+	} else
+		retval = generic_permission(inode, submask, NULL);
+
+	if (retval && retval != -EROFS)	/* ignore EROFS */
+		return retval;
+
+	retval = security_inode_permission(inode, mask, nd);
+	return ((retval == -EROFS) ? 0 : retval);	/* ignore EROFS */
+}
+
+static int unionfs_permission(struct inode *inode, int mask,
+			      struct nameidata *nd)
+{
+	struct inode *hidden_inode = NULL;
+	int err = 0;
+	int bindex, bstart, bend;
+	const int is_file = !S_ISDIR(inode->i_mode);
+	const int write_mask = (mask & MAY_WRITE) && !(mask & MAY_READ);
+
+	bstart = ibstart(inode);
+	bend = ibend(inode);
+
+	for (bindex = bstart; bindex <= bend; bindex++) {
+		hidden_inode = unionfs_lower_inode_idx(inode, bindex);
+		if (!hidden_inode)
+			continue;
+
+		/* check the condition for D-F-D underlying files/directories,
+		 * we dont have to check for files, if we are checking for
+		 * directories.
+		 */
+		if (!is_file && !S_ISDIR(hidden_inode->i_mode))
+			continue;
+
+		/* We use our own special version of permission, such that
+		 * only the first branch returns -EROFS.
+		 */
+		err = inode_permission(hidden_inode, mask, nd, bindex);
+
+		/* The permissions are an intersection of the overall directory
+		 * permissions, so we fail if one fails.
+		 */
+		if (err)
+			goto out;
+
+		/* only the leftmost file matters. */
+		if (is_file || write_mask) {
+			if (is_file && write_mask) {
+				err = get_write_access(hidden_inode);
+				if (!err)
+					put_write_access(hidden_inode);
+			}
+			break;
+		}
+	}
+
+out:
+	return err;
+}
+
+static int unionfs_setattr(struct dentry *dentry, struct iattr *ia)
+{
+	int err = 0;
+	struct dentry *hidden_dentry;
+	struct inode *inode = NULL;
+	struct inode *hidden_inode = NULL;
+	int bstart, bend, bindex;
+	int i;
+	int copyup = 0;
+
+	lock_dentry(dentry);
+	bstart = dbstart(dentry);
+	bend = dbend(dentry);
+	inode = dentry->d_inode;
+
+	for (bindex = bstart; (bindex <= bend) || (bindex == bstart); bindex++) {
+		hidden_dentry = unionfs_lower_dentry_idx(dentry, bindex);
+		if (!hidden_dentry)
+			continue;
+		BUG_ON(hidden_dentry->d_inode == NULL);
+
+		/* If the file is on a read only branch */
+		if (is_robranch_super(dentry->d_sb, bindex)
+		    || IS_RDONLY(hidden_dentry->d_inode)) {
+			if (copyup || (bindex != bstart))
+				continue;
+			/* Only if its the leftmost file, copyup the file */
+			for (i = bstart - 1; i >= 0; i--) {
+				loff_t size = dentry->d_inode->i_size;
+				if (ia->ia_valid & ATTR_SIZE)
+					size = ia->ia_size;
+				err = copyup_dentry(dentry->d_parent->d_inode,
+						    dentry, bstart, i, NULL,
+						    size);
+
+				if (!err) {
+					copyup = 1;
+					hidden_dentry = unionfs_lower_dentry(dentry);
+					break;
+				}
+				/* if error is in the leftmost branch, pass it up */
+				if (i == 0)
+					goto out;
+			}
+
+		}
+		err = notify_change(hidden_dentry, ia);
+		if (err)
+			goto out;
+		break;
+	}
+
+	/* get the size from the first hidden inode */
+	hidden_inode = unionfs_lower_inode(dentry->d_inode);
+	fsstack_copy_attr_all(inode, hidden_inode, unionfs_get_nlinks);
+	fsstack_copy_inode_size(inode, hidden_inode);
+
+out:
+	unlock_dentry(dentry);
+	return err;
+}
+
+struct inode_operations unionfs_symlink_iops = {
+	.readlink	= unionfs_readlink,
+	.permission	= unionfs_permission,
+	.follow_link	= unionfs_follow_link,
+	.setattr	= unionfs_setattr,
+	.put_link	= unionfs_put_link,
+};
+
+struct inode_operations unionfs_dir_iops = {
+	.create		= unionfs_create,
+	.lookup		= unionfs_lookup,
+	.link		= unionfs_link,
+	.unlink		= unionfs_unlink,
+	.symlink	= unionfs_symlink,
+	.mkdir		= unionfs_mkdir,
+	.rmdir		= unionfs_rmdir,
+	.mknod		= unionfs_mknod,
+	.rename		= unionfs_rename,
+	.permission	= unionfs_permission,
+	.setattr	= unionfs_setattr,
+};
+
+struct inode_operations unionfs_main_iops = {
+	.permission	= unionfs_permission,
+	.setattr	= unionfs_setattr,
+};
+
-- 
1.4.4.2

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