symlink.c

Go to the documentation of this file.

/*
 * 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 <[email protected]>
 *
 * This file is released under the GPLv2.
 *
 * Please see Documentation/filesystems/sysfs.txt for more information.
 */

#include <linux/fs.h>
#include <linux/gfp.h>
#include <linux/mount.h>
#include <linux/module.h>
#include <linux/kobject.h>
#include <linux/namei.h>
#include <linux/mutex.h>
#include <linux/security.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;
    enum kobj_ns_type ns_type;
    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;

    ns_type = sysfs_ns_type(parent_sd);
    if (ns_type)
        sd->s_ns = target->ktype->namespace(target);
    sd->s_symlink.target_sd = target_sd;
    target_sd = NULL;   /* reference is now owned by the symlink */

    sysfs_addrm_start(&acxt, parent_sd);
    /* Symlinks must be between directories with the same ns_type */
    if (!ns_type ||
        (ns_type == sysfs_ns_type(sd->s_symlink.target_sd->s_parent))) {
        if (warn)
            error = sysfs_add_one(&acxt, sd);
        else
            error = __sysfs_add_one(&acxt, sd);
    } else {
        error = -EINVAL;
        WARN(1, KERN_WARNING
            "sysfs: symlink across ns_types %s/%s -> %s/%s\n",
            parent_sd->s_name,
            sd->s_name,
            sd->s_symlink.target_sd->s_parent->s_name,
            sd->s_symlink.target_sd->s_name);
    }
    sysfs_addrm_finish(&acxt);

    if (error)
        goto out_put;

    return 0;

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

int sysfs_create_link(struct kobject *kobj, struct kobject *target,
              const char *name)
{
    return sysfs_do_create_link(kobj, target, name, 1);
}

int sysfs_create_link_nowarn(struct kobject *kobj, struct kobject *target,
                 const char *name)
{
    return sysfs_do_create_link(kobj, target, name, 0);
}

void sysfs_delete_link(struct kobject *kobj, struct kobject *targ,
            const char *name)
{
    const void *ns = NULL;
    spin_lock(&sysfs_assoc_lock);
    if (targ->sd && sysfs_ns_type(kobj->sd))
        ns = targ->sd->s_ns;
    spin_unlock(&sysfs_assoc_lock);
    sysfs_hash_and_remove(kobj->sd, ns, name);
}

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, NULL, name);
}

int sysfs_rename_link(struct kobject *kobj, struct kobject *targ,
            const char *old, const char *new)
{
    struct sysfs_dirent *parent_sd, *sd = NULL;
    const void *old_ns = NULL, *new_ns = NULL;
    int result;

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

    if (targ->sd)
        old_ns = targ->sd->s_ns;

    result = -ENOENT;
    sd = sysfs_get_dirent(parent_sd, old_ns, old);
    if (!sd)
        goto out;

    result = -EINVAL;
    if (sysfs_type(sd) != SYSFS_KOBJ_LINK)
        goto out;
    if (sd->s_symlink.target_sd->s_dir.kobj != targ)
        goto out;

    if (sysfs_ns_type(parent_sd))
        new_ns = targ->ktype->namespace(targ);

    result = sysfs_rename(sd, parent_sd, new_ns, new);

out:
    sysfs_put(sd);
    return result;
}

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); 
        if (error < 0)
            free_page((unsigned long)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 = {
    .setxattr   = sysfs_setxattr,
    .readlink   = generic_readlink,
    .follow_link    = sysfs_follow_link,
    .put_link   = sysfs_put_link,
    .setattr    = sysfs_setattr,
    .getattr    = sysfs_getattr,
    .permission = sysfs_permission,
};


EXPORT_SYMBOL_GPL(sysfs_create_link);
EXPORT_SYMBOL_GPL(sysfs_remove_link);
EXPORT_SYMBOL_GPL(sysfs_rename_link);