[PATCH] configfs: User-driven configuration filesystem
Configfs, a file system for userspace-driven kernel object configuration.
The OCFS2 stack makes extensive use of this for propagation of cluster
configuration information into kernel.
Signed-off-by: Joel Becker <joel.becker@oracle.com>
diff --git a/fs/configfs/symlink.c b/fs/configfs/symlink.c
new file mode 100644
index 0000000..50f5840
--- /dev/null
+++ b/fs/configfs/symlink.c
@@ -0,0 +1,281 @@
+/* -*- 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/configfs.h>
+#include "configfs_internal.h"
+
+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;
+ strncpy(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 = -ENOMEM;
+ sl = kmalloc(sizeof(struct configfs_symlink), GFP_KERNEL);
+ if (sl) {
+ sl->sl_target = config_item_get(item);
+ /* FIXME: needs a lock, I'd bet */
+ list_add(&sl->sl_list, &target_sd->s_links);
+ ret = configfs_create_link(sl, parent_item->ci_dentry,
+ dentry);
+ if (ret) {
+ list_del_init(&sl->sl_list);
+ config_item_put(item);
+ kfree(sl);
+ }
+ }
+
+ return ret;
+}
+
+
+static int get_target(const char *symname, struct nameidata *nd,
+ struct config_item **target)
+{
+ int ret;
+
+ ret = path_lookup(symname, LOOKUP_FOLLOW|LOOKUP_DIRECTORY, nd);
+ if (!ret) {
+ if (nd->dentry->d_sb == configfs_sb) {
+ *target = configfs_get_config_item(nd->dentry);
+ if (!*target) {
+ ret = -ENOENT;
+ path_release(nd);
+ }
+ } else
+ ret = -EPERM;
+ }
+
+ return ret;
+}
+
+
+int configfs_symlink(struct inode *dir, struct dentry *dentry, const char *symname)
+{
+ int ret;
+ struct nameidata nd;
+ struct config_item *parent_item;
+ struct config_item *target_item;
+ struct config_item_type *type;
+
+ ret = -EPERM; /* What lack-of-symlink returns */
+ if (dentry->d_parent == configfs_sb->s_root)
+ goto out;
+
+ parent_item = configfs_get_config_item(dentry->d_parent);
+ type = parent_item->ci_type;
+
+ if (!type || !type->ct_item_ops ||
+ !type->ct_item_ops->allow_link)
+ goto out_put;
+
+ ret = get_target(symname, &nd, &target_item);
+ if (ret)
+ goto out_put;
+
+ ret = type->ct_item_ops->allow_link(parent_item, target_item);
+ if (!ret)
+ ret = create_link(parent_item, target_item, dentry);
+
+ config_item_put(target_item);
+ path_release(&nd);
+
+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;
+
+ if (dentry->d_parent == configfs_sb->s_root)
+ BUG();
+
+ sl = sd->s_element;
+
+ parent_item = configfs_get_config_item(dentry->d_parent);
+ type = parent_item->ci_type;
+
+ list_del_init(&sd->s_sibling);
+ 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);
+
+ /* FIXME: Needs lock */
+ list_del_init(&sl->sl_list);
+
+ /* 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", __FUNCTION__, depth, size);
+
+ for (s = path; depth--; s += 3)
+ strcpy(s,"../");
+
+ fill_item_path(target, path, size);
+ pr_debug("%s: path = '%s'\n", __FUNCTION__, 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 void *configfs_follow_link(struct dentry *dentry, struct nameidata *nd)
+{
+ int error = -ENOMEM;
+ unsigned long page = get_zeroed_page(GFP_KERNEL);
+
+ if (page) {
+ error = configfs_getlink(dentry, (char *)page);
+ if (!error) {
+ nd_set_link(nd, (char *)page);
+ return (void *)page;
+ }
+ }
+
+ nd_set_link(nd, ERR_PTR(error));
+ return NULL;
+}
+
+static void configfs_put_link(struct dentry *dentry, struct nameidata *nd,
+ void *cookie)
+{
+ if (cookie) {
+ unsigned long page = (unsigned long)cookie;
+ free_page(page);
+ }
+}
+
+struct inode_operations configfs_symlink_inode_operations = {
+ .follow_link = configfs_follow_link,
+ .readlink = generic_readlink,
+ .put_link = configfs_put_link,
+};
+