xref: /openbmc/linux/fs/sysfs/symlink.c (revision e868d61272caa648214046a096e5a6bfc068dc8c)
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 #include <asm/semaphore.h>
11 
12 #include "sysfs.h"
13 
14 static int object_depth(struct kobject * kobj)
15 {
16 	struct kobject * p = kobj;
17 	int depth = 0;
18 	do { depth++; } while ((p = p->parent));
19 	return depth;
20 }
21 
22 static int object_path_length(struct kobject * kobj)
23 {
24 	struct kobject * p = kobj;
25 	int length = 1;
26 	do {
27 		length += strlen(kobject_name(p)) + 1;
28 		p = p->parent;
29 	} while (p);
30 	return length;
31 }
32 
33 static void fill_object_path(struct kobject * kobj, char * buffer, int length)
34 {
35 	struct kobject * p;
36 
37 	--length;
38 	for (p = kobj; p; p = p->parent) {
39 		int cur = strlen(kobject_name(p));
40 
41 		/* back up enough to print this bus id with '/' */
42 		length -= cur;
43 		strncpy(buffer + length,kobject_name(p),cur);
44 		*(buffer + --length) = '/';
45 	}
46 }
47 
48 static int sysfs_add_link(struct dentry * parent, const char * name, struct kobject * target)
49 {
50 	struct sysfs_dirent * parent_sd = parent->d_fsdata;
51 	struct sysfs_symlink * sl;
52 	int error = 0;
53 
54 	error = -ENOMEM;
55 	sl = kmalloc(sizeof(*sl), GFP_KERNEL);
56 	if (!sl)
57 		goto exit1;
58 
59 	sl->link_name = kmalloc(strlen(name) + 1, GFP_KERNEL);
60 	if (!sl->link_name)
61 		goto exit2;
62 
63 	strcpy(sl->link_name, name);
64 	sl->target_kobj = kobject_get(target);
65 
66 	error = sysfs_make_dirent(parent_sd, NULL, sl, S_IFLNK|S_IRWXUGO,
67 				SYSFS_KOBJ_LINK);
68 	if (!error)
69 		return 0;
70 
71 	kobject_put(target);
72 	kfree(sl->link_name);
73 exit2:
74 	kfree(sl);
75 exit1:
76 	return error;
77 }
78 
79 /**
80  *	sysfs_create_link - create symlink between two objects.
81  *	@kobj:	object whose directory we're creating the link in.
82  *	@target:	object we're pointing to.
83  *	@name:		name of the symlink.
84  */
85 int sysfs_create_link(struct kobject * kobj, struct kobject * target, const char * name)
86 {
87 	struct dentry *dentry = NULL;
88 	int error = -EEXIST;
89 
90 	BUG_ON(!name);
91 
92 	if (!kobj) {
93 		if (sysfs_mount && sysfs_mount->mnt_sb)
94 			dentry = sysfs_mount->mnt_sb->s_root;
95 	} else
96 		dentry = kobj->dentry;
97 
98 	if (!dentry)
99 		return -EFAULT;
100 
101 	mutex_lock(&dentry->d_inode->i_mutex);
102 	if (!sysfs_dirent_exist(dentry->d_fsdata, name))
103 		error = sysfs_add_link(dentry, name, target);
104 	mutex_unlock(&dentry->d_inode->i_mutex);
105 	return error;
106 }
107 
108 
109 /**
110  *	sysfs_remove_link - remove symlink in object's directory.
111  *	@kobj:	object we're acting for.
112  *	@name:	name of the symlink to remove.
113  */
114 
115 void sysfs_remove_link(struct kobject * kobj, const char * name)
116 {
117 	sysfs_hash_and_remove(kobj->dentry,name);
118 }
119 
120 static int sysfs_get_target_path(struct kobject * kobj, struct kobject * target,
121 				 char *path)
122 {
123 	char * s;
124 	int depth, size;
125 
126 	depth = object_depth(kobj);
127 	size = object_path_length(target) + depth * 3 - 1;
128 	if (size > PATH_MAX)
129 		return -ENAMETOOLONG;
130 
131 	pr_debug("%s: depth = %d, size = %d\n", __FUNCTION__, depth, size);
132 
133 	for (s = path; depth--; s += 3)
134 		strcpy(s,"../");
135 
136 	fill_object_path(target, path, size);
137 	pr_debug("%s: path = '%s'\n", __FUNCTION__, path);
138 
139 	return 0;
140 }
141 
142 static int sysfs_getlink(struct dentry *dentry, char * path)
143 {
144 	struct kobject *kobj, *target_kobj;
145 	int error = 0;
146 
147 	kobj = sysfs_get_kobject(dentry->d_parent);
148 	if (!kobj)
149 		return -EINVAL;
150 
151 	target_kobj = sysfs_get_kobject(dentry);
152 	if (!target_kobj) {
153 		kobject_put(kobj);
154 		return -EINVAL;
155 	}
156 
157 	down_read(&sysfs_rename_sem);
158 	error = sysfs_get_target_path(kobj, target_kobj, path);
159 	up_read(&sysfs_rename_sem);
160 
161 	kobject_put(kobj);
162 	kobject_put(target_kobj);
163 	return error;
164 
165 }
166 
167 static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd)
168 {
169 	int error = -ENOMEM;
170 	unsigned long page = get_zeroed_page(GFP_KERNEL);
171 	if (page)
172 		error = sysfs_getlink(dentry, (char *) page);
173 	nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
174 	return NULL;
175 }
176 
177 static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
178 {
179 	char *page = nd_get_link(nd);
180 	if (!IS_ERR(page))
181 		free_page((unsigned long)page);
182 }
183 
184 const struct inode_operations sysfs_symlink_inode_operations = {
185 	.readlink = generic_readlink,
186 	.follow_link = sysfs_follow_link,
187 	.put_link = sysfs_put_link,
188 };
189 
190 
191 EXPORT_SYMBOL_GPL(sysfs_create_link);
192 EXPORT_SYMBOL_GPL(sysfs_remove_link);
193