1 files changed, 335 insertions, 0 deletions
diff --git a/fs/configfs/symlink.c b/fs/configfs/symlink.c
new file mode 100644
index 000000000000..3af565e8fd51
--- /dev/null
+++ b/fs/configfs/symlink.c
@@ -0,0 +1,335 @@
+/* -*- mode: c; c-basic-offset: 8; -*-
+ * vim: noexpandtab sw=8 ts=8 sts=0:
+ *
+ * symlink.c - operations for configfs symlinks.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ *
+ * Based on sysfs:
+ * 	sysfs is Copyright (C) 2001, 2002, 2003 Patrick Mochel
+ *
+ * configfs Copyright (C) 2005 Oracle.  All rights reserved.
+ */
+
+#include <linux/fs.h>
+#include <linux/module.h>
+#include <linux/namei.h>
+#include <linux/slab.h>
+
+#include <linux/configfs.h>
+#include "configfs_internal.h"
+
+/* Protects attachments of new symlinks */
+DEFINE_MUTEX(configfs_symlink_mutex);
+
+static int item_depth(struct config_item * item)
+{
+	struct config_item * p = item;
+	int depth = 0;
+	do { depth++; } while ((p = p->ci_parent) && !configfs_is_root(p));
+	return depth;
+}
+
+static int item_path_length(struct config_item * item)
+{
+	struct config_item * p = item;
+	int length = 1;
+	do {
+		length += strlen(config_item_name(p)) + 1;
+		p = p->ci_parent;
+	} while (p && !configfs_is_root(p));
+	return length;
+}
+
+static void fill_item_path(struct config_item * item, char * buffer, int length)
+{
+	struct config_item * p;
+
+	--length;
+	for (p = item; p && !configfs_is_root(p); p = p->ci_parent) {
+		int cur = strlen(config_item_name(p));
+
+		/* back up enough to print this bus id with '/' */
+		length -= cur;
+		memcpy(buffer + length, config_item_name(p), cur);
+		*(buffer + --length) = '/';
+	}
+}
+
+static int create_link(struct config_item *parent_item,
+		       struct config_item *item,
+		       struct dentry *dentry)
+{
+	struct configfs_dirent *target_sd = item->ci_dentry->d_fsdata;
+	struct configfs_symlink *sl;
+	int ret;
+
+	ret = -ENOENT;
+	if (!configfs_dirent_is_ready(target_sd))
+		goto out;
+	ret = -ENOMEM;
+	sl = kmalloc(sizeof(struct configfs_symlink), GFP_KERNEL);
+	if (sl) {
+		spin_lock(&configfs_dirent_lock);
+		if (target_sd->s_type & CONFIGFS_USET_DROPPING) {
+			spin_unlock(&configfs_dirent_lock);
+			kfree(sl);
+			return -ENOENT;
+		}
+		sl->sl_target = config_item_get(item);
+		list_add(&sl->sl_list, &target_sd->s_links);
+		spin_unlock(&configfs_dirent_lock);
+		ret = configfs_create_link(sl, parent_item->ci_dentry,
+					   dentry);
+		if (ret) {
+			spin_lock(&configfs_dirent_lock);
+			list_del_init(&sl->sl_list);
+			spin_unlock(&configfs_dirent_lock);
+			config_item_put(item);
+			kfree(sl);
+		}
+	}
+
+out:
+	return ret;
+}
+
+
+static int get_target(const char *symname, struct path *path,
+		      struct config_item **target, struct super_block *sb)
+{
+	int ret;
+
+	ret = kern_path(symname, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, path);
+	if (!ret) {
+		if (path->dentry->d_sb == sb) {
+			*target = configfs_get_config_item(path->dentry);
+			if (!*target) {
+				ret = -ENOENT;
+				path_put(path);
+			}
+		} else {
+			ret = -EPERM;
+			path_put(path);
+		}
+	}
+
+	return ret;
+}
+
+
+int configfs_symlink(struct inode *dir, struct dentry *dentry, const char *symname)
+{
+	int ret;
+	struct path path;
+	struct configfs_dirent *sd;
+	struct config_item *parent_item;
+	struct config_item *target_item = NULL;
+	struct config_item_type *type;
+
+	sd = dentry->d_parent->d_fsdata;
+	/*
+	 * Fake invisibility if dir belongs to a group/default groups hierarchy
+	 * being attached
+	 */
+	ret = -ENOENT;
+	if (!configfs_dirent_is_ready(sd))
+		goto out;
+
+	parent_item = configfs_get_config_item(dentry->d_parent);
+	type = parent_item->ci_type;
+
+	ret = -EPERM;
+	if (!type || !type->ct_item_ops ||
+	    !type->ct_item_ops->allow_link)
+		goto out_put;
+
+	/*
+	 * This is really sick.  What they wanted was a hybrid of
+	 * link(2) and symlink(2) - they wanted the target resolved
+	 * at syscall time (as link(2) would've done), be a directory
+	 * (which link(2) would've refused to do) *AND* be a deep
+	 * fucking magic, making the target busy from rmdir POV.
+	 * symlink(2) is nothing of that sort, and the locking it
+	 * gets matches the normal symlink(2) semantics.  Without
+	 * attempts to resolve the target (which might very well
+	 * not even exist yet) done prior to locking the parent
+	 * directory.  This perversion, OTOH, needs to resolve
+	 * the target, which would lead to obvious deadlocks if
+	 * attempted with any directories locked.
+	 *
+	 * Unfortunately, that garbage is userland ABI and we should've
+	 * said "no" back in 2005.  Too late now, so we get to
+	 * play very ugly games with locking.
+	 *
+	 * Try *ANYTHING* of that sort in new code, and you will
+	 * really regret it.  Just ask yourself - what could a BOFH
+	 * do to me and do I want to find it out first-hand?
+	 *
+	 *  AV, a thoroughly annoyed bastard.
+	 */
+	inode_unlock(dir);
+	ret = get_target(symname, &path, &target_item, dentry->d_sb);
+	inode_lock(dir);
+	if (ret)
+		goto out_put;
+
+	if (dentry->d_inode || d_unhashed(dentry))
+		ret = -EEXIST;
+	else
+		ret = inode_permission(dir, MAY_WRITE | MAY_EXEC);
+	if (!ret)
+		ret = type->ct_item_ops->allow_link(parent_item, target_item);
+	if (!ret) {
+		mutex_lock(&configfs_symlink_mutex);
+		ret = create_link(parent_item, target_item, dentry);
+		mutex_unlock(&configfs_symlink_mutex);
+		if (ret && type->ct_item_ops->drop_link)
+			type->ct_item_ops->drop_link(parent_item,
+						     target_item);
+	}
+
+	config_item_put(target_item);
+	path_put(&path);
+
+out_put:
+	config_item_put(parent_item);
+
+out:
+	return ret;
+}
+
+int configfs_unlink(struct inode *dir, struct dentry *dentry)
+{
+	struct configfs_dirent *sd = dentry->d_fsdata;
+	struct configfs_symlink *sl;
+	struct config_item *parent_item;
+	struct config_item_type *type;
+	int ret;
+
+	ret = -EPERM;  /* What lack-of-symlink returns */
+	if (!(sd->s_type & CONFIGFS_ITEM_LINK))
+		goto out;
+
+	sl = sd->s_element;
+
+	parent_item = configfs_get_config_item(dentry->d_parent);
+	type = parent_item->ci_type;
+
+	spin_lock(&configfs_dirent_lock);
+	list_del_init(&sd->s_sibling);
+	spin_unlock(&configfs_dirent_lock);
+	configfs_drop_dentry(sd, dentry->d_parent);
+	dput(dentry);
+	configfs_put(sd);
+
+	/*
+	 * drop_link() must be called before
+	 * list_del_init(&sl->sl_list), so that the order of
+	 * drop_link(this, target) and drop_item(target) is preserved.
+	 */
+	if (type && type->ct_item_ops &&
+	    type->ct_item_ops->drop_link)
+		type->ct_item_ops->drop_link(parent_item,
+					       sl->sl_target);
+
+	spin_lock(&configfs_dirent_lock);
+	list_del_init(&sl->sl_list);
+	spin_unlock(&configfs_dirent_lock);
+
+	/* Put reference from create_link() */
+	config_item_put(sl->sl_target);
+	kfree(sl);
+
+	config_item_put(parent_item);
+
+	ret = 0;
+
+out:
+	return ret;
+}
+
+static int configfs_get_target_path(struct config_item * item, struct config_item * target,
+				   char *path)
+{
+	char * s;
+	int depth, size;
+
+	depth = item_depth(item);
+	size = item_path_length(target) + depth * 3 - 1;
+	if (size > PATH_MAX)
+		return -ENAMETOOLONG;
+
+	pr_debug("%s: depth = %d, size = %d\n", __func__, depth, size);
+
+	for (s = path; depth--; s += 3)
+		strcpy(s,"../");
+
+	fill_item_path(target, path, size);
+	pr_debug("%s: path = '%s'\n", __func__, path);
+
+	return 0;
+}
+
+static int configfs_getlink(struct dentry *dentry, char * path)
+{
+	struct config_item *item, *target_item;
+	int error = 0;
+
+	item = configfs_get_config_item(dentry->d_parent);
+	if (!item)
+		return -EINVAL;
+
+	target_item = configfs_get_config_item(dentry);
+	if (!target_item) {
+		config_item_put(item);
+		return -EINVAL;
+	}
+
+	down_read(&configfs_rename_sem);
+	error = configfs_get_target_path(item, target_item, path);
+	up_read(&configfs_rename_sem);
+
+	config_item_put(item);
+	config_item_put(target_item);
+	return error;
+
+}
+
+static const char *configfs_follow_link(struct dentry *dentry, void **cookie)
+{
+	unsigned long page = get_zeroed_page(GFP_KERNEL);
+	int error;
+
+	if (!page)
+		return ERR_PTR(-ENOMEM);
+
+	error = configfs_getlink(dentry, (char *)page);
+	if (!error) {
+		return *cookie = (void *)page;
+	}
+
+	free_page(page);
+	return ERR_PTR(error);
+}
+
+const struct inode_operations configfs_symlink_inode_operations = {
+	.follow_link = configfs_follow_link,
+	.readlink = generic_readlink,
+	.put_link = free_page_put_link,
+	.setattr = configfs_setattr,
+};
+