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 */
25struct 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	int error;
31
32	kn = kernfs_new_node(parent, name, S_IFLNK|S_IRWXUGO, KERNFS_LINK);
33	if (!kn)
34		return ERR_PTR(-ENOMEM);
35
36	if (kernfs_ns_enabled(parent))
37		kn->ns = target->ns;
38	kn->symlink.target_kn = target;
39	kernfs_get(target);	/* ref owned by symlink */
40
41	error = kernfs_add_one(kn);
42	if (!error)
43		return kn;
44
45	kernfs_put(kn);
46	return ERR_PTR(error);
47}
48
49static int kernfs_get_target_path(struct kernfs_node *parent,
50				  struct kernfs_node *target, char *path)
51{
52	struct kernfs_node *base, *kn;
53	char *s = path;
54	int len = 0;
55
56	/* go up to the root, stop at the base */
57	base = parent;
58	while (base->parent) {
59		kn = target->parent;
60		while (kn->parent && base != kn)
61			kn = kn->parent;
62
63		if (base == kn)
64			break;
65
66		strcpy(s, "../");
67		s += 3;
68		base = base->parent;
69	}
70
71	/* determine end of target string for reverse fillup */
72	kn = target;
73	while (kn->parent && kn != base) {
74		len += strlen(kn->name) + 1;
75		kn = kn->parent;
76	}
77
78	/* check limits */
79	if (len < 2)
80		return -EINVAL;
81	len--;
82	if ((s - path) + len > PATH_MAX)
83		return -ENAMETOOLONG;
84
85	/* reverse fillup of target string from target to base */
86	kn = target;
87	while (kn->parent && kn != base) {
88		int slen = strlen(kn->name);
89
90		len -= slen;
91		strncpy(s + len, kn->name, slen);
92		if (len)
93			s[--len] = '/';
94
95		kn = kn->parent;
96	}
97
98	return 0;
99}
100
101static int kernfs_getlink(struct dentry *dentry, char *path)
102{
103	struct kernfs_node *kn = dentry->d_fsdata;
104	struct kernfs_node *parent = kn->parent;
105	struct kernfs_node *target = kn->symlink.target_kn;
106	int error;
107
108	mutex_lock(&kernfs_mutex);
109	error = kernfs_get_target_path(parent, target, path);
110	mutex_unlock(&kernfs_mutex);
111
112	return error;
113}
114
115static void *kernfs_iop_follow_link(struct dentry *dentry, struct nameidata *nd)
116{
117	int error = -ENOMEM;
118	unsigned long page = get_zeroed_page(GFP_KERNEL);
119	if (page) {
120		error = kernfs_getlink(dentry, (char *) page);
121		if (error < 0)
122			free_page((unsigned long)page);
123	}
124	nd_set_link(nd, error ? ERR_PTR(error) : (char *)page);
125	return NULL;
126}
127
128static void kernfs_iop_put_link(struct dentry *dentry, struct nameidata *nd,
129				void *cookie)
130{
131	char *page = nd_get_link(nd);
132	if (!IS_ERR(page))
133		free_page((unsigned long)page);
134}
135
136const struct inode_operations kernfs_symlink_iops = {
137	.setxattr	= kernfs_iop_setxattr,
138	.removexattr	= kernfs_iop_removexattr,
139	.getxattr	= kernfs_iop_getxattr,
140	.listxattr	= kernfs_iop_listxattr,
141	.readlink	= generic_readlink,
142	.follow_link	= kernfs_iop_follow_link,
143	.put_link	= kernfs_iop_put_link,
144	.setattr	= kernfs_iop_setattr,
145	.getattr	= kernfs_iop_getattr,
146	.permission	= kernfs_iop_permission,
147};
148