xref: /openbmc/linux/fs/kernfs/symlink.c (revision 9b9c2cd4)
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   */
25  struct 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  
49  static 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  
101  static 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  
115  static const char *kernfs_iop_follow_link(struct dentry *dentry, void **cookie)
116  {
117  	int error = -ENOMEM;
118  	unsigned long page = get_zeroed_page(GFP_KERNEL);
119  	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);
125  	}
126  	return *cookie = (char *)page;
127  }
128  
129  const struct inode_operations kernfs_symlink_iops = {
130  	.setxattr	= kernfs_iop_setxattr,
131  	.removexattr	= kernfs_iop_removexattr,
132  	.getxattr	= kernfs_iop_getxattr,
133  	.listxattr	= kernfs_iop_listxattr,
134  	.readlink	= generic_readlink,
135  	.follow_link	= kernfs_iop_follow_link,
136  	.put_link	= free_page_put_link,
137  	.setattr	= kernfs_iop_setattr,
138  	.getattr	= kernfs_iop_getattr,
139  	.permission	= kernfs_iop_permission,
140  };
141