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 = sysfs_new_dirent(kernfs_root(parent), name, S_IFLNK|S_IRWXUGO,
  34                               SYSFS_KOBJ_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         sysfs_addrm_start(&acxt);
  44         error = sysfs_add_one(&acxt, kn, parent);
  45         sysfs_addrm_finish(&acxt);
  46
  47         if (!error)
  48                 return kn;
  49
  50         kernfs_put(kn);
  51         return ERR_PTR(error);
  52 }
  53
  54 static int sysfs_get_target_path(struct kernfs_node *parent,
  55                                  struct kernfs_node *target, char *path)
  56 {
  57         struct kernfs_node *base, *kn;
  58         char *s = path;
  59         int len = 0;
  60
  61         /* go up to the root, stop at the base */
  62         base = parent;
  63         while (base->parent) {
  64                 kn = target->parent;
  65                 while (kn->parent && base != kn)
  66                         kn = kn->parent;
  67
  68                 if (base == kn)
  69                         break;
  70
  71                 strcpy(s, "../");
  72                 s += 3;
  73                 base = base->parent;
  74         }
  75
  76         /* determine end of target string for reverse fillup */
  77         kn = target;
  78         while (kn->parent && kn != base) {
  79                 len += strlen(kn->name) + 1;
  80                 kn = kn->parent;
  81         }
  82
  83         /* check limits */
  84         if (len < 2)
  85                 return -EINVAL;
  86         len--;
  87         if ((s - path) + len > PATH_MAX)
  88                 return -ENAMETOOLONG;
  89
  90         /* reverse fillup of target string from target to base */
  91         kn = target;
  92         while (kn->parent && kn != base) {
  93                 int slen = strlen(kn->name);
  94
  95                 len -= slen;
  96                 strncpy(s + len, kn->name, slen);
  97                 if (len)
  98                         s[--len] = '/';
  99
 100                 kn = kn->parent;
 101         }
 102
 103         return 0;
 104 }
 105
 106 static int sysfs_getlink(struct dentry *dentry, char *path)
 107 {
 108         struct kernfs_node *kn = dentry->d_fsdata;
 109         struct kernfs_node *parent = kn->parent;
 110         struct kernfs_node *target = kn->symlink.target_kn;
 111         int error;
 112
 113         mutex_lock(&sysfs_mutex);
 114         error = sysfs_get_target_path(parent, target, path);
 115         mutex_unlock(&sysfs_mutex);
 116
 117         return error;
 118 }
 119
 120 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
 121 {
 122         int error = -ENOMEM;
 123         unsigned long page = get_zeroed_page(GFP_KERNEL);
 124         if (page) {
 125                 error = sysfs_getlink(dentry, (char *) page);
 126                 if (error < 0)
 127                         free_page((unsigned long)page);
 128         }
 129         nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
 130         return NULL;
 131 }
 132
 133 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd,
 134                            void *cookie)
 135 {
 136         char *page = nd_get_link(nd);
 137         if (!IS_ERR(page))
 138                 free_page((unsigned long)page);
 139 }
 140
 141 const struct inode_operations sysfs_symlink_inode_operations = {
 142         .setxattr       = sysfs_setxattr,
 143         .removexattr    = sysfs_removexattr,
 144         .getxattr       = sysfs_getxattr,
 145         .listxattr      = sysfs_listxattr,
 146         .readlink       = generic_readlink,
 147         .follow_link    = sysfs_follow_link,
 148         .put_link       = sysfs_put_link,
 149         .setattr        = sysfs_setattr,
 150         .getattr        = sysfs_getattr,
 151         .permission     = sysfs_permission,
 152 };