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b8441ed2 TH |
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 | */ | |
2072f1af TH |
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 | */ | |
25 | struct sysfs_dirent *kernfs_create_link(struct sysfs_dirent *parent, | |
26 | const char *name, | |
27 | struct sysfs_dirent *target) | |
28 | { | |
29 | struct sysfs_dirent *sd; | |
30 | struct sysfs_addrm_cxt acxt; | |
31 | int error; | |
32 | ||
33 | sd = sysfs_new_dirent(name, S_IFLNK|S_IRWXUGO, SYSFS_KOBJ_LINK); | |
34 | if (!sd) | |
35 | return ERR_PTR(-ENOMEM); | |
36 | ||
37 | if (parent->s_flags & SYSFS_FLAG_NS) | |
38 | sd->s_ns = target->s_ns; | |
39 | sd->s_symlink.target_sd = target; | |
40 | kernfs_get(target); /* ref owned by symlink */ | |
41 | ||
42 | sysfs_addrm_start(&acxt); | |
43 | error = sysfs_add_one(&acxt, sd, parent); | |
44 | sysfs_addrm_finish(&acxt); | |
45 | ||
46 | if (!error) | |
47 | return sd; | |
48 | ||
49 | kernfs_put(sd); | |
50 | return ERR_PTR(error); | |
51 | } | |
52 | ||
53 | static int sysfs_get_target_path(struct sysfs_dirent *parent_sd, | |
54 | struct sysfs_dirent *target_sd, char *path) | |
55 | { | |
56 | struct sysfs_dirent *base, *sd; | |
57 | char *s = path; | |
58 | int len = 0; | |
59 | ||
60 | /* go up to the root, stop at the base */ | |
61 | base = parent_sd; | |
62 | while (base->s_parent) { | |
63 | sd = target_sd->s_parent; | |
64 | while (sd->s_parent && base != sd) | |
65 | sd = sd->s_parent; | |
66 | ||
67 | if (base == sd) | |
68 | break; | |
69 | ||
70 | strcpy(s, "../"); | |
71 | s += 3; | |
72 | base = base->s_parent; | |
73 | } | |
74 | ||
75 | /* determine end of target string for reverse fillup */ | |
76 | sd = target_sd; | |
77 | while (sd->s_parent && sd != base) { | |
78 | len += strlen(sd->s_name) + 1; | |
79 | sd = sd->s_parent; | |
80 | } | |
81 | ||
82 | /* check limits */ | |
83 | if (len < 2) | |
84 | return -EINVAL; | |
85 | len--; | |
86 | if ((s - path) + len > PATH_MAX) | |
87 | return -ENAMETOOLONG; | |
88 | ||
89 | /* reverse fillup of target string from target to base */ | |
90 | sd = target_sd; | |
91 | while (sd->s_parent && sd != base) { | |
92 | int slen = strlen(sd->s_name); | |
93 | ||
94 | len -= slen; | |
95 | strncpy(s + len, sd->s_name, slen); | |
96 | if (len) | |
97 | s[--len] = '/'; | |
98 | ||
99 | sd = sd->s_parent; | |
100 | } | |
101 | ||
102 | return 0; | |
103 | } | |
104 | ||
105 | static int sysfs_getlink(struct dentry *dentry, char *path) | |
106 | { | |
107 | struct sysfs_dirent *sd = dentry->d_fsdata; | |
108 | struct sysfs_dirent *parent_sd = sd->s_parent; | |
109 | struct sysfs_dirent *target_sd = sd->s_symlink.target_sd; | |
110 | int error; | |
111 | ||
112 | mutex_lock(&sysfs_mutex); | |
113 | error = sysfs_get_target_path(parent_sd, target_sd, path); | |
114 | mutex_unlock(&sysfs_mutex); | |
115 | ||
116 | return error; | |
117 | } | |
118 | ||
119 | static void *sysfs_follow_link(struct dentry *dentry, struct nameidata *nd) | |
120 | { | |
121 | int error = -ENOMEM; | |
122 | unsigned long page = get_zeroed_page(GFP_KERNEL); | |
123 | if (page) { | |
124 | error = sysfs_getlink(dentry, (char *) page); | |
125 | if (error < 0) | |
126 | free_page((unsigned long)page); | |
127 | } | |
128 | nd_set_link(nd, error ? ERR_PTR(error) : (char *)page); | |
129 | return NULL; | |
130 | } | |
131 | ||
132 | static void sysfs_put_link(struct dentry *dentry, struct nameidata *nd, | |
133 | void *cookie) | |
134 | { | |
135 | char *page = nd_get_link(nd); | |
136 | if (!IS_ERR(page)) | |
137 | free_page((unsigned long)page); | |
138 | } | |
139 | ||
140 | const struct inode_operations sysfs_symlink_inode_operations = { | |
141 | .setxattr = sysfs_setxattr, | |
142 | .readlink = generic_readlink, | |
143 | .follow_link = sysfs_follow_link, | |
144 | .put_link = sysfs_put_link, | |
145 | .setattr = sysfs_setattr, | |
146 | .getattr = sysfs_getattr, | |
147 | .permission = sysfs_permission, | |
148 | }; |