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