SYSFS: allow sysfs_create_link to create symlinks in the root of sysfs
[linux-2.6] / fs / sysfs / symlink.c
1 /*
2  * symlink.c - operations for sysfs symlinks.
3  */
4
5 #include <linux/fs.h>
6 #include <linux/mount.h>
7 #include <linux/module.h>
8 #include <linux/kobject.h>
9 #include <linux/namei.h>
10
11 #include "sysfs.h"
12
13 static int object_depth(struct kobject * kobj)
14 {
15         struct kobject * p = kobj;
16         int depth = 0;
17         do { depth++; } while ((p = p->parent));
18         return depth;
19 }
20
21 static int object_path_length(struct kobject * kobj)
22 {
23         struct kobject * p = kobj;
24         int length = 1;
25         do {
26                 length += strlen(kobject_name(p)) + 1;
27                 p = p->parent;
28         } while (p);
29         return length;
30 }
31
32 static void fill_object_path(struct kobject * kobj, char * buffer, int length)
33 {
34         struct kobject * p;
35
36         --length;
37         for (p = kobj; p; p = p->parent) {
38                 int cur = strlen(kobject_name(p));
39
40                 /* back up enough to print this bus id with '/' */
41                 length -= cur;
42                 strncpy(buffer + length,kobject_name(p),cur);
43                 *(buffer + --length) = '/';
44         }
45 }
46
47 static int sysfs_add_link(struct dentry * parent, const char * name, struct kobject * target)
48 {
49         struct sysfs_dirent * parent_sd = parent->d_fsdata;
50         struct sysfs_symlink * sl;
51         int error = 0;
52
53         error = -ENOMEM;
54         sl = kmalloc(sizeof(*sl), GFP_KERNEL);
55         if (!sl)
56                 goto exit1;
57
58         sl->link_name = kmalloc(strlen(name) + 1, GFP_KERNEL);
59         if (!sl->link_name)
60                 goto exit2;
61
62         strcpy(sl->link_name, name);
63         sl->target_kobj = kobject_get(target);
64
65         error = sysfs_make_dirent(parent_sd, NULL, sl, S_IFLNK|S_IRWXUGO,
66                                 SYSFS_KOBJ_LINK);
67         if (!error)
68                 return 0;
69
70         kobject_put(target);
71         kfree(sl->link_name);
72 exit2:
73         kfree(sl);
74 exit1:
75         return error;
76 }
77
78 /**
79  *      sysfs_create_link - create symlink between two objects.
80  *      @kobj:  object whose directory we're creating the link in.
81  *      @target:        object we're pointing to.
82  *      @name:          name of the symlink.
83  */
84 int sysfs_create_link(struct kobject * kobj, struct kobject * target, const char * name)
85 {
86         struct dentry *dentry = NULL;
87         int error = -EEXIST;
88
89         BUG_ON(!name);
90
91         if (!kobj) {
92                 if (sysfs_mount && sysfs_mount->mnt_sb)
93                         dentry = sysfs_mount->mnt_sb->s_root;
94         } else
95                 dentry = kobj->dentry;
96
97         if (!dentry)
98                 return -EFAULT;
99
100         mutex_lock(&dentry->d_inode->i_mutex);
101         if (!sysfs_dirent_exist(dentry->d_fsdata, name))
102                 error = sysfs_add_link(dentry, name, target);
103         mutex_unlock(&dentry->d_inode->i_mutex);
104         return error;
105 }
106
107
108 /**
109  *      sysfs_remove_link - remove symlink in object's directory.
110  *      @kobj:  object we're acting for.
111  *      @name:  name of the symlink to remove.
112  */
113
114 void sysfs_remove_link(struct kobject * kobj, const char * name)
115 {
116         sysfs_hash_and_remove(kobj->dentry,name);
117 }
118
119 static int sysfs_get_target_path(struct kobject * kobj, struct kobject * target,
120                                  char *path)
121 {
122         char * s;
123         int depth, size;
124
125         depth = object_depth(kobj);
126         size = object_path_length(target) + depth * 3 - 1;
127         if (size > PATH_MAX)
128                 return -ENAMETOOLONG;
129
130         pr_debug("%s: depth = %d, size = %d\n", __FUNCTION__, depth, size);
131
132         for (s = path; depth--; s += 3)
133                 strcpy(s,"../");
134
135         fill_object_path(target, path, size);
136         pr_debug("%s: path = '%s'\n", __FUNCTION__, path);
137
138         return 0;
139 }
140
141 static int sysfs_getlink(struct dentry *dentry, char * path)
142 {
143         struct kobject *kobj, *target_kobj;
144         int error = 0;
145
146         kobj = sysfs_get_kobject(dentry->d_parent);
147         if (!kobj)
148                 return -EINVAL;
149
150         target_kobj = sysfs_get_kobject(dentry);
151         if (!target_kobj) {
152                 kobject_put(kobj);
153                 return -EINVAL;
154         }
155
156         down_read(&sysfs_rename_sem);
157         error = sysfs_get_target_path(kobj, target_kobj, path);
158         up_read(&sysfs_rename_sem);
159         
160         kobject_put(kobj);
161         kobject_put(target_kobj);
162         return error;
163
164 }
165
166 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
167 {
168         int error = -ENOMEM;
169         unsigned long page = get_zeroed_page(GFP_KERNEL);
170         if (page)
171                 error = sysfs_getlink(dentry, (char *) page); 
172         nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
173         return NULL;
174 }
175
176 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
177 {
178         char *page = nd_get_link(nd);
179         if (!IS_ERR(page))
180                 free_page((unsigned long)page);
181 }
182
183 struct inode_operations sysfs_symlink_inode_operations = {
184         .readlink = generic_readlink,
185         .follow_link = sysfs_follow_link,
186         .put_link = sysfs_put_link,
187 };
188
189
190 EXPORT_SYMBOL_GPL(sysfs_create_link);
191 EXPORT_SYMBOL_GPL(sysfs_remove_link);