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         struct kernfs_addrm_cxt acxt;
  31         int error;
  32
  33         kn = kernfs_new_node(kernfs_root(parent), name, S_IFLNK|S_IRWXUGO,
  34                              KERNFS_LINK);
  35         if (!kn)
  36                 return ERR_PTR(-ENOMEM);
  37
  38         if (kernfs_ns_enabled(parent))
  39                 kn->ns = target->ns;
  40         kn->symlink.target_kn = target;
  41         kernfs_get(target);     /* ref owned by symlink */
  42
  43         error = -ENOENT;
  44         if (kernfs_get_active(parent)) {
  45                 kernfs_addrm_start(&acxt);
  46                 error = kernfs_add_one(&acxt, kn, parent);
  47                 kernfs_addrm_finish(&acxt);
  48                 kernfs_put_active(parent);
  49         }
  50
  51         if (!error)
  52                 return kn;
  53
  54         kernfs_put(kn);
  55         return ERR_PTR(error);
  56 }
  57
  58 static int kernfs_get_target_path(struct kernfs_node *parent,
  59                                   struct kernfs_node *target, char *path)
  60 {
  61         struct kernfs_node *base, *kn;
  62         char *s = path;
  63         int len = 0;
  64
  65         /* go up to the root, stop at the base */
  66         base = parent;
  67         while (base->parent) {
  68                 kn = target->parent;
  69                 while (kn->parent && base != kn)
  70                         kn = kn->parent;
  71
  72                 if (base == kn)
  73                         break;
  74
  75                 strcpy(s, "../");
  76                 s += 3;
  77                 base = base->parent;
  78         }
  79
  80         /* determine end of target string for reverse fillup */
  81         kn = target;
  82         while (kn->parent && kn != base) {
  83                 len += strlen(kn->name) + 1;
  84                 kn = kn->parent;
  85         }
  86
  87         /* check limits */
  88         if (len < 2)
  89                 return -EINVAL;
  90         len--;
  91         if ((s - path) + len > PATH_MAX)
  92                 return -ENAMETOOLONG;
  93
  94         /* reverse fillup of target string from target to base */
  95         kn = target;
  96         while (kn->parent && kn != base) {
  97                 int slen = strlen(kn->name);
  98
  99                 len -= slen;
 100                 strncpy(s + len, kn->name, slen);
 101                 if (len)
 102                         s[--len] = '/';
 103
 104                 kn = kn->parent;
 105         }
 106
 107         return 0;
 108 }
 109
 110 static int kernfs_getlink(struct dentry *dentry, char *path)
 111 {
 112         struct kernfs_node *kn = dentry->d_fsdata;
 113         struct kernfs_node *parent = kn->parent;
 114         struct kernfs_node *target = kn->symlink.target_kn;
 115         int error;
 116
 117         mutex_lock(&kernfs_mutex);
 118         error = kernfs_get_target_path(parent, target, path);
 119         mutex_unlock(&kernfs_mutex);
 120
 121         return error;
 122 }
 123
 124 static void *kernfs_iop_follow_link(struct dentry *dentry, struct nameidata *nd)
 125 {
 126         int error = -ENOMEM;
 127         unsigned long page = get_zeroed_page(GFP_KERNEL);
 128         if (page) {
 129                 error = kernfs_getlink(dentry, (char *) page);
 130                 if (error < 0)
 131                         free_page((unsigned long)page);
 132         }
 133         nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
 134         return NULL;
 135 }
 136
 137 static void kernfs_iop_put_link(struct dentry *dentry, struct nameidata *nd,
 138                                 void *cookie)
 139 {
 140         char *page = nd_get_link(nd);
 141         if (!IS_ERR(page))
 142                 free_page((unsigned long)page);
 143 }
 144
 145 const struct inode_operations kernfs_symlink_iops = {
 146         .setxattr       = kernfs_iop_setxattr,
 147         .removexattr    = kernfs_iop_removexattr,
 148         .getxattr       = kernfs_iop_getxattr,
 149         .listxattr      = kernfs_iop_listxattr,
 150         .readlink       = generic_readlink,
 151         .follow_link    = kernfs_iop_follow_link,
 152         .put_link       = kernfs_iop_put_link,
 153         .setattr        = kernfs_iop_setattr,
 154         .getattr        = kernfs_iop_getattr,
 155         .permission     = kernfs_iop_permission,
 156 };