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  */
  25 struct 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
  49 static 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
 101 static 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
 115 static 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
 128 static 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
 136 const 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 };