LXR linux/fs/kernfs/symlink.c

   1/*
   2 * fs/kernfs/symlink.c - kernfs symlink implementation
   3 *
   4 * Copyright (c) 2001-3 Patrick Mochel
   5 * Copyright (c) 2007 SUSE Linux Products GmbH
   6 * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
   7 *
   8 * This file is released under the GPLv2.
   9 */
  10
  11#include <linux/fs.h>
  12#include <linux/gfp.h>
  13#include <linux/namei.h>
  14
  15#include "kernfs-internal.h"
  16
  17/**
  18 * kernfs_create_link - create a symlink
  19 * @parent: directory to create the symlink in
  20 * @name: name of the symlink
  21 * @target: target node for the symlink to point to
  22 *
  23 * Returns the created node on success, ERR_PTR() value on error.
  24 */
  25struct kernfs_node *kernfs_create_link(struct kernfs_node *parent,
  26                                       const char *name,
  27                                       struct kernfs_node *target)
  28{
  29        struct kernfs_node *kn;
  30        int error;
  31
  32        kn = kernfs_new_node(parent, name, S_IFLNK|S_IRWXUGO, KERNFS_LINK);
  33        if (!kn)
  34                return ERR_PTR(-ENOMEM);
  35
  36        if (kernfs_ns_enabled(parent))
  37                kn->ns = target->ns;
  38        kn->symlink.target_kn = target;
  39        kernfs_get(target);     /* ref owned by symlink */
  40
  41        error = kernfs_add_one(kn);
  42        if (!error)
  43                return kn;
  44
  45        kernfs_put(kn);
  46        return ERR_PTR(error);
  47}
  48
  49static int kernfs_get_target_path(struct kernfs_node *parent,
  50                                  struct kernfs_node *target, char *path)
  51{
  52        struct kernfs_node *base, *kn;
  53        char *s = path;
  54        int len = 0;
  55
  56        /* go up to the root, stop at the base */
  57        base = parent;
  58        while (base->parent) {
  59                kn = target->parent;
  60                while (kn->parent && base != kn)
  61                        kn = kn->parent;
  62
  63                if (base == kn)
  64                        break;
  65
  66                strcpy(s, "../");
  67                s += 3;
  68                base = base->parent;
  69        }
  70
  71        /* determine end of target string for reverse fillup */
  72        kn = target;
  73        while (kn->parent && kn != base) {
  74                len += strlen(kn->name) + 1;
  75                kn = kn->parent;
  76        }
  77
  78        /* check limits */
  79        if (len < 2)
  80                return -EINVAL;
  81        len--;
  82        if ((s - path) + len > PATH_MAX)
  83                return -ENAMETOOLONG;
  84
  85        /* reverse fillup of target string from target to base */
  86        kn = target;
  87        while (kn->parent && kn != base) {
  88                int slen = strlen(kn->name);
  89
  90                len -= slen;
  91                strncpy(s + len, kn->name, slen);
  92                if (len)
  93                        s[--len] = '/';
  94
  95                kn = kn->parent;
  96        }
  97
  98        return 0;
  99}
 100
 101static int kernfs_getlink(struct dentry *dentry, char *path)
 102{
 103        struct kernfs_node *kn = dentry->d_fsdata;
 104        struct kernfs_node *parent = kn->parent;
 105        struct kernfs_node *target = kn->symlink.target_kn;
 106        int error;
 107
 108        mutex_lock(&kernfs_mutex);
 109        error = kernfs_get_target_path(parent, target, path);
 110        mutex_unlock(&kernfs_mutex);
 111
 112        return error;
 113}
 114
 115static void *kernfs_iop_follow_link(struct dentry *dentry, struct nameidata *nd)
 116{
 117        int error = -ENOMEM;
 118        unsigned long page = get_zeroed_page(GFP_KERNEL);
 119        if (page) {
 120                error = kernfs_getlink(dentry, (char *) page);
 121                if (error < 0)
 122                        free_page((unsigned long)page);
 123        }
 124        nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
 125        return NULL;
 126}
 127
 128static void kernfs_iop_put_link(struct dentry *dentry, struct nameidata *nd,
 129                                void *cookie)
 130{
 131        char *page = nd_get_link(nd);
 132        if (!IS_ERR(page))
 133                free_page((unsigned long)page);
 134}
 135
 136const struct inode_operations kernfs_symlink_iops = {
 137        .setxattr       = kernfs_iop_setxattr,
 138        .removexattr    = kernfs_iop_removexattr,
 139        .getxattr       = kernfs_iop_getxattr,
 140        .listxattr      = kernfs_iop_listxattr,
 141        .readlink       = generic_readlink,
 142        .follow_link    = kernfs_iop_follow_link,
 143        .put_link       = kernfs_iop_put_link,
 144        .setattr        = kernfs_iop_setattr,
 145        .getattr        = kernfs_iop_getattr,
 146        .permission     = kernfs_iop_permission,
 147};
 148