root/fs/sysfs/symlink.c

DEFINITIONS

1. sysfs_do_create_link
2. sysfs_create_link
3. sysfs_create_link_nowarn
4. sysfs_remove_link
5. sysfs_get_target_path
6. sysfs_getlink
7. sysfs_follow_link
8. sysfs_put_link

/*
 * fs/sysfs/symlink.c - sysfs symlink implementation
 *
 * Copyright (c) 2001-3 Patrick Mochel
 * Copyright (c) 2007 SUSE Linux Products GmbH
 * Copyright (c) 2007 Tejun Heo <teheo@suse.de>
 *
 * This file is released under the GPLv2.
 *
 * Please see Documentation/filesystems/sysfs.txt for more information.
 */

#include <linux/fs.h>
#include <linux/mount.h>
#include <linux/module.h>
#include <linux/kobject.h>
#include <linux/namei.h>
#include <linux/mutex.h>

#include "sysfs.h"

static int sysfs_do_create_link(struct kobject *kobj, struct kobject *target,
                                const char *name, int warn)
{
        struct sysfs_dirent *parent_sd = NULL;
        struct sysfs_dirent *target_sd = NULL;
        struct sysfs_dirent *sd = NULL;
        struct sysfs_addrm_cxt acxt;
        int error;

        BUG_ON(!name);

        if (!kobj)
                parent_sd = &sysfs_root;
        else
                parent_sd = kobj->sd;

        error = -EFAULT;
        if (!parent_sd)
                goto out_put;

        /* target->sd can go away beneath us but is protected with
         * sysfs_assoc_lock.  Fetch target_sd from it.
         */
        spin_lock(&sysfs_assoc_lock);
        if (target->sd)
                target_sd = sysfs_get(target->sd);
        spin_unlock(&sysfs_assoc_lock);

        error = -ENOENT;
        if (!target_sd)
                goto out_put;

        error = -ENOMEM;
        sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK);
        if (!sd)
                goto out_put;

        sd->s_symlink.target_sd = target_sd;
        target_sd = NULL;       /* reference is now owned by the symlink */

        sysfs_addrm_start(&acxt, parent_sd);
        if (warn)
                error = sysfs_add_one(&acxt, sd);
        else
                error = __sysfs_add_one(&acxt, sd);
        sysfs_addrm_finish(&acxt);

        if (error)
                goto out_put;

        return 0;

 out_put:
        sysfs_put(target_sd);
        sysfs_put(sd);
        return error;
}

/**
 *      sysfs_create_link - create symlink between two objects.
 *      @kobj:  object whose directory we're creating the link in.
 *      @target:        object we're pointing to.
 *      @name:          name of the symlink.
 */
int sysfs_create_link(struct kobject *kobj, struct kobject *target,
                      const char *name)
{
        return sysfs_do_create_link(kobj, target, name, 1);
}

/**
 *      sysfs_create_link_nowarn - create symlink between two objects.
 *      @kobj:  object whose directory we're creating the link in.
 *      @target:        object we're pointing to.
 *      @name:          name of the symlink.
 *
 *      This function does the same as sysf_create_link(), but it
 *      doesn't warn if the link already exists.
 */
int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target,
                             const char *name)
{
        return sysfs_do_create_link(kobj, target, name, 0);
}

/**
 *      sysfs_remove_link - remove symlink in object's directory.
 *      @kobj:  object we're acting for.
 *      @name:  name of the symlink to remove.
 */

void sysfs_remove_link(struct kobject * kobj, const char * name)
{
        struct sysfs_dirent *parent_sd = NULL;

        if (!kobj)
                parent_sd = &sysfs_root;
        else
                parent_sd = kobj->sd;

        sysfs_hash_and_remove(parent_sd, name);
}

static int sysfs_get_target_path(struct sysfs_dirent *parent_sd,
                                 struct sysfs_dirent *target_sd, char *path)
{
        struct sysfs_dirent *base, *sd;
        char *s = path;
        int len = 0;

        /* go up to the root, stop at the base */
        base = parent_sd;
        while (base->s_parent) {
                sd = target_sd->s_parent;
                while (sd->s_parent && base != sd)
                        sd = sd->s_parent;

                if (base == sd)
                        break;

                strcpy(s, "../");
                s += 3;
                base = base->s_parent;
        }

        /* determine end of target string for reverse fillup */
        sd = target_sd;
        while (sd->s_parent && sd != base) {
                len += strlen(sd->s_name) + 1;
                sd = sd->s_parent;
        }

        /* check limits */
        if (len < 2)
                return -EINVAL;
        len--;
        if ((s - path) + len > PATH_MAX)
                return -ENAMETOOLONG;

        /* reverse fillup of target string from target to base */
        sd = target_sd;
        while (sd->s_parent && sd != base) {
                int slen = strlen(sd->s_name);

                len -= slen;
                strncpy(s + len, sd->s_name, slen);
                if (len)
                        s[--len] = '/';

                sd = sd->s_parent;
        }

        return 0;
}

static int sysfs_getlink(struct dentry *dentry, char * path)
{
        struct sysfs_dirent *sd = dentry->d_fsdata;
        struct sysfs_dirent *parent_sd = sd->s_parent;
        struct sysfs_dirent *target_sd = sd->s_symlink.target_sd;
        int error;

        mutex_lock(&sysfs_mutex);
        error = sysfs_get_target_path(parent_sd, target_sd, path);
        mutex_unlock(&sysfs_mutex);

        return error;
}

static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
{
        int error = -ENOMEM;
        unsigned long page = get_zeroed_page(GFP_KERNEL);
        if (page)
                error = sysfs_getlink(dentry, (char *) page); 
        nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
        return NULL;
}

static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
{
        char *page = nd_get_link(nd);
        if (!IS_ERR(page))
                free_page((unsigned long)page);
}

const struct inode_operations sysfs_symlink_inode_operations = {
        .readlink = generic_readlink,
        .follow_link = sysfs_follow_link,
        .put_link = sysfs_put_link,
};


EXPORT_SYMBOL_GPL(sysfs_create_link);
EXPORT_SYMBOL_GPL(sysfs_remove_link);