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Linux/fs/kernfs/symlink.c

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  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  * Ownership of the link matches ownership of the target.
 25  */
 26 struct kernfs_node *kernfs_create_link(struct kernfs_node *parent,
 27                                        const char *name,
 28                                        struct kernfs_node *target)
 29 {
 30         struct kernfs_node *kn;
 31         int error;
 32         kuid_t uid = GLOBAL_ROOT_UID;
 33         kgid_t gid = GLOBAL_ROOT_GID;
 34 
 35         if (target->iattr) {
 36                 uid = target->iattr->ia_iattr.ia_uid;
 37                 gid = target->iattr->ia_iattr.ia_gid;
 38         }
 39 
 40         kn = kernfs_new_node(parent, name, S_IFLNK|S_IRWXUGO, uid, gid,
 41                              KERNFS_LINK);
 42         if (!kn)
 43                 return ERR_PTR(-ENOMEM);
 44 
 45         if (kernfs_ns_enabled(parent))
 46                 kn->ns = target->ns;
 47         kn->symlink.target_kn = target;
 48         kernfs_get(target);     /* ref owned by symlink */
 49 
 50         error = kernfs_add_one(kn);
 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                 if ((s - path) + 3 >= PATH_MAX)
 76                         return -ENAMETOOLONG;
 77 
 78                 strcpy(s, "../");
 79                 s += 3;
 80                 base = base->parent;
 81         }
 82 
 83         /* determine end of target string for reverse fillup */
 84         kn = target;
 85         while (kn->parent && kn != base) {
 86                 len += strlen(kn->name) + 1;
 87                 kn = kn->parent;
 88         }
 89 
 90         /* check limits */
 91         if (len < 2)
 92                 return -EINVAL;
 93         len--;
 94         if ((s - path) + len >= PATH_MAX)
 95                 return -ENAMETOOLONG;
 96 
 97         /* reverse fillup of target string from target to base */
 98         kn = target;
 99         while (kn->parent && kn != base) {
100                 int slen = strlen(kn->name);
101 
102                 len -= slen;
103                 memcpy(s + len, kn->name, slen);
104                 if (len)
105                         s[--len] = '/';
106 
107                 kn = kn->parent;
108         }
109 
110         return 0;
111 }
112 
113 static int kernfs_getlink(struct inode *inode, char *path)
114 {
115         struct kernfs_node *kn = inode->i_private;
116         struct kernfs_node *parent = kn->parent;
117         struct kernfs_node *target = kn->symlink.target_kn;
118         int error;
119 
120         mutex_lock(&kernfs_mutex);
121         error = kernfs_get_target_path(parent, target, path);
122         mutex_unlock(&kernfs_mutex);
123 
124         return error;
125 }
126 
127 static const char *kernfs_iop_get_link(struct dentry *dentry,
128                                        struct inode *inode,
129                                        struct delayed_call *done)
130 {
131         char *body;
132         int error;
133 
134         if (!dentry)
135                 return ERR_PTR(-ECHILD);
136         body = kzalloc(PAGE_SIZE, GFP_KERNEL);
137         if (!body)
138                 return ERR_PTR(-ENOMEM);
139         error = kernfs_getlink(inode, body);
140         if (unlikely(error < 0)) {
141                 kfree(body);
142                 return ERR_PTR(error);
143         }
144         set_delayed_call(done, kfree_link, body);
145         return body;
146 }
147 
148 const struct inode_operations kernfs_symlink_iops = {
149         .listxattr      = kernfs_iop_listxattr,
150         .get_link       = kernfs_iop_get_link,
151         .setattr        = kernfs_iop_setattr,
152         .getattr        = kernfs_iop_getattr,
153         .permission     = kernfs_iop_permission,
154 };
155 

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