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Tejun Heob8441ed2013-11-24 09:54:58 -05001/*
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 */
Tejun Heo2072f1a2013-11-28 14:54:35 -050010
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 */
Tejun Heo324a56e2013-12-11 14:11:53 -050025struct kernfs_node *kernfs_create_link(struct kernfs_node *parent,
26 const char *name,
27 struct kernfs_node *target)
Tejun Heo2072f1a2013-11-28 14:54:35 -050028{
Tejun Heo324a56e2013-12-11 14:11:53 -050029 struct kernfs_node *kn;
Tejun Heo2072f1a2013-11-28 14:54:35 -050030 int error;
31
Tejun Heodb4aad22014-01-17 09:58:25 -050032 kn = kernfs_new_node(parent, name, S_IFLNK|S_IRWXUGO, KERNFS_LINK);
Tejun Heo324a56e2013-12-11 14:11:53 -050033 if (!kn)
Tejun Heo2072f1a2013-11-28 14:54:35 -050034 return ERR_PTR(-ENOMEM);
35
Tejun Heoac9bba02013-11-29 17:19:09 -050036 if (kernfs_ns_enabled(parent))
Tejun Heoadc5e8b2013-12-11 14:11:54 -050037 kn->ns = target->ns;
38 kn->symlink.target_kn = target;
Tejun Heo2072f1a2013-11-28 14:54:35 -050039 kernfs_get(target); /* ref owned by symlink */
40
Tejun Heo988cd7a2014-02-03 14:02:58 -050041 error = kernfs_add_one(kn);
Tejun Heo2072f1a2013-11-28 14:54:35 -050042 if (!error)
Tejun Heo324a56e2013-12-11 14:11:53 -050043 return kn;
Tejun Heo2072f1a2013-11-28 14:54:35 -050044
Tejun Heo324a56e2013-12-11 14:11:53 -050045 kernfs_put(kn);
Tejun Heo2072f1a2013-11-28 14:54:35 -050046 return ERR_PTR(error);
47}
48
Tejun Heoc637b8a2013-12-11 14:11:58 -050049static int kernfs_get_target_path(struct kernfs_node *parent,
50 struct kernfs_node *target, char *path)
Tejun Heo2072f1a2013-11-28 14:54:35 -050051{
Tejun Heo324a56e2013-12-11 14:11:53 -050052 struct kernfs_node *base, *kn;
Tejun Heo2072f1a2013-11-28 14:54:35 -050053 char *s = path;
54 int len = 0;
55
56 /* go up to the root, stop at the base */
Tejun Heo324a56e2013-12-11 14:11:53 -050057 base = parent;
Tejun Heoadc5e8b2013-12-11 14:11:54 -050058 while (base->parent) {
59 kn = target->parent;
60 while (kn->parent && base != kn)
61 kn = kn->parent;
Tejun Heo2072f1a2013-11-28 14:54:35 -050062
Tejun Heo324a56e2013-12-11 14:11:53 -050063 if (base == kn)
Tejun Heo2072f1a2013-11-28 14:54:35 -050064 break;
65
66 strcpy(s, "../");
67 s += 3;
Tejun Heoadc5e8b2013-12-11 14:11:54 -050068 base = base->parent;
Tejun Heo2072f1a2013-11-28 14:54:35 -050069 }
70
71 /* determine end of target string for reverse fillup */
Tejun Heo324a56e2013-12-11 14:11:53 -050072 kn = target;
Tejun Heoadc5e8b2013-12-11 14:11:54 -050073 while (kn->parent && kn != base) {
74 len += strlen(kn->name) + 1;
75 kn = kn->parent;
Tejun Heo2072f1a2013-11-28 14:54:35 -050076 }
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 */
Tejun Heo324a56e2013-12-11 14:11:53 -050086 kn = target;
Tejun Heoadc5e8b2013-12-11 14:11:54 -050087 while (kn->parent && kn != base) {
88 int slen = strlen(kn->name);
Tejun Heo2072f1a2013-11-28 14:54:35 -050089
90 len -= slen;
Tejun Heoadc5e8b2013-12-11 14:11:54 -050091 strncpy(s + len, kn->name, slen);
Tejun Heo2072f1a2013-11-28 14:54:35 -050092 if (len)
93 s[--len] = '/';
94
Tejun Heoadc5e8b2013-12-11 14:11:54 -050095 kn = kn->parent;
Tejun Heo2072f1a2013-11-28 14:54:35 -050096 }
97
98 return 0;
99}
100
Tejun Heoc637b8a2013-12-11 14:11:58 -0500101static int kernfs_getlink(struct dentry *dentry, char *path)
Tejun Heo2072f1a2013-11-28 14:54:35 -0500102{
Tejun Heo324a56e2013-12-11 14:11:53 -0500103 struct kernfs_node *kn = dentry->d_fsdata;
Tejun Heoadc5e8b2013-12-11 14:11:54 -0500104 struct kernfs_node *parent = kn->parent;
105 struct kernfs_node *target = kn->symlink.target_kn;
Tejun Heo2072f1a2013-11-28 14:54:35 -0500106 int error;
107
Tejun Heoa797bfc2013-12-11 14:11:57 -0500108 mutex_lock(&kernfs_mutex);
Tejun Heoc637b8a2013-12-11 14:11:58 -0500109 error = kernfs_get_target_path(parent, target, path);
Tejun Heoa797bfc2013-12-11 14:11:57 -0500110 mutex_unlock(&kernfs_mutex);
Tejun Heo2072f1a2013-11-28 14:54:35 -0500111
112 return error;
113}
114
Al Viro6e771372015-05-02 13:37:52 -0400115static const char *kernfs_iop_follow_link(struct dentry *dentry, void **cookie)
Tejun Heo2072f1a2013-11-28 14:54:35 -0500116{
117 int error = -ENOMEM;
118 unsigned long page = get_zeroed_page(GFP_KERNEL);
Al Viro680baac2015-05-02 13:32:22 -0400119 if (!page)
120 return ERR_PTR(-ENOMEM);
121 error = kernfs_getlink(dentry, (char *)page);
122 if (unlikely(error < 0)) {
123 free_page((unsigned long)page);
124 return ERR_PTR(error);
Tejun Heo2072f1a2013-11-28 14:54:35 -0500125 }
Al Viro680baac2015-05-02 13:32:22 -0400126 return *cookie = (char *)page;
Tejun Heo2072f1a2013-11-28 14:54:35 -0500127}
128
Tejun Heoa797bfc2013-12-11 14:11:57 -0500129const struct inode_operations kernfs_symlink_iops = {
Tejun Heoc637b8a2013-12-11 14:11:58 -0500130 .setxattr = kernfs_iop_setxattr,
131 .removexattr = kernfs_iop_removexattr,
132 .getxattr = kernfs_iop_getxattr,
133 .listxattr = kernfs_iop_listxattr,
Tejun Heo2072f1a2013-11-28 14:54:35 -0500134 .readlink = generic_readlink,
Tejun Heoc637b8a2013-12-11 14:11:58 -0500135 .follow_link = kernfs_iop_follow_link,
Al Viroecc087f2015-05-07 11:19:14 -0400136 .put_link = free_page_put_link,
Tejun Heoc637b8a2013-12-11 14:11:58 -0500137 .setattr = kernfs_iop_setattr,
138 .getattr = kernfs_iop_getattr,
139 .permission = kernfs_iop_permission,
Tejun Heo2072f1a2013-11-28 14:54:35 -0500140};