symlink.c

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/* -*- 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;
        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 = -ENOENT;
    if (!configfs_dirent_is_ready(target_sd))
        goto out;
    ret = -ENOMEM;
    sl = kmalloc(sizeof(struct configfs_symlink), GFP_KERNEL);
    if (sl) {
        sl->sl_target = config_item_get(item);
        spin_lock(&configfs_dirent_lock);
        if (target_sd->s_type & CONFIGFS_USET_DROPPING) {
            spin_unlock(&configfs_dirent_lock);
            config_item_put(item);
            kfree(sl);
            return -ENOENT;
        }
        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;

    ret = get_target(symname, &path, &target_item, dentry->d_sb);
    if (ret)
        goto out_put;

    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 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);
    }
}

const struct inode_operations configfs_symlink_inode_operations = {
    .follow_link = configfs_follow_link,
    .readlink = generic_readlink,
    .put_link = configfs_put_link,
    .setattr = configfs_setattr,
};