1 /*-
2 * SPDX-License-Identifier: BSD-2-Clause
3 *
4 * Copyright (c) 2022, Jake Freeland <jfree@freebsd.org>
5 *
6 * Redistribution and use in source and binary forms, with or without
7 * modification, are permitted provided that the following conditions
8 * are met:
9 * 1. Redistributions of source code must retain the above copyright
10 * notice, this list of conditions and the following disclaimer.
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
14 *
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
16 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
17 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
18 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
19 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
20 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
21 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
22 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
23 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
24 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
25 * SUCH DAMAGE.
26 */
27
28 #include <sys/types.h>
29 #include <linux/fs.h>
30
31 MALLOC_DEFINE(M_LSATTR, "simple_attr", "Linux Simple Attribute File");
32
33 struct simple_attr {
34 int (*get)(void *, uint64_t *);
35 int (*set)(void *, uint64_t);
36 void *data;
37 const char *fmt;
38 struct mutex mutex;
39 };
40
41 /*
42 * simple_attr_open: open and populate simple attribute data
43 *
44 * @inode: file inode
45 * @filp: file pointer
46 * @get: ->get() for reading file data
47 * @set: ->set() for writing file data
48 * @fmt: format specifier for data returned by @get
49 *
50 * Memory allocate a simple_attr and appropriately initialize its members.
51 * The simple_attr must be stored in filp->private_data.
52 * Simple attr files do not support seeking. Open the file as nonseekable.
53 *
54 * Return value: simple attribute file descriptor
55 */
56 int
simple_attr_open(struct inode * inode,struct file * filp,int (* get)(void *,uint64_t *),int (* set)(void *,uint64_t),const char * fmt)57 simple_attr_open(struct inode *inode, struct file *filp,
58 int (*get)(void *, uint64_t *), int (*set)(void *, uint64_t),
59 const char *fmt)
60 {
61 struct simple_attr *sattr;
62 sattr = malloc(sizeof(*sattr), M_LSATTR, M_ZERO | M_NOWAIT);
63 if (sattr == NULL)
64 return (-ENOMEM);
65
66 sattr->get = get;
67 sattr->set = set;
68 sattr->data = inode->i_private;
69 sattr->fmt = fmt;
70 mutex_init(&sattr->mutex);
71
72 filp->private_data = (void *) sattr;
73
74 return (nonseekable_open(inode, filp));
75 }
76
77 int
simple_attr_release(struct inode * inode,struct file * filp)78 simple_attr_release(struct inode *inode, struct file *filp)
79 {
80 free(filp->private_data, M_LSATTR);
81 return (0);
82 }
83
84 /*
85 * simple_attr_read: read simple attr data and transfer into buffer
86 *
87 * @filp: file pointer
88 * @buf: kernel space buffer
89 * @read_size: number of bytes to be transferred
90 * @ppos: starting pointer position for transfer
91 *
92 * The simple_attr structure is stored in filp->private_data.
93 * ->get() retrieves raw file data.
94 * The ->fmt specifier can format this data to be human readable.
95 * This output is then transferred into the @buf buffer.
96 *
97 * Return value:
98 * On success, number of bytes transferred
99 * On failure, negative signed ERRNO
100 */
101 ssize_t
simple_attr_read(struct file * filp,char * buf,size_t read_size,loff_t * ppos)102 simple_attr_read(struct file *filp, char *buf, size_t read_size, loff_t *ppos)
103 {
104 struct simple_attr *sattr;
105 uint64_t data;
106 ssize_t ret;
107 char prebuf[24];
108
109 sattr = filp->private_data;
110
111 if (sattr->get == NULL)
112 return (-EFAULT);
113
114 mutex_lock(&sattr->mutex);
115
116 ret = sattr->get(sattr->data, &data);
117 if (ret)
118 goto unlock;
119
120 scnprintf(prebuf, sizeof(prebuf), sattr->fmt, data);
121
122 ret = strlen(prebuf) + 1;
123 if (*ppos >= ret || read_size < 1) {
124 ret = -EINVAL;
125 goto unlock;
126 }
127
128 read_size = min(ret - *ppos, read_size);
129 ret = strscpy(buf, prebuf + *ppos, read_size);
130
131 /* add 1 for null terminator */
132 if (ret > 0)
133 ret += 1;
134
135 unlock:
136 mutex_unlock(&sattr->mutex);
137 return (ret);
138 }
139
140 /*
141 * simple_attr_write: write contents of buffer into simple attribute file
142 *
143 * @filp: file pointer
144 * @buf: kernel space buffer
145 * @write_size: number bytes to be transferred
146 * @ppos: starting pointer position for transfer
147 *
148 * The simple_attr structure is stored in filp->private_data.
149 * Convert the @buf string to unsigned long long.
150 * ->set() writes unsigned long long data into the simple attr file.
151 *
152 * Return value:
153 * On success, number of bytes written to simple attr
154 * On failure, negative signed ERRNO
155 */
156 ssize_t
simple_attr_write(struct file * filp,const char * buf,size_t write_size,loff_t * ppos)157 simple_attr_write(struct file *filp, const char *buf, size_t write_size, loff_t *ppos)
158 {
159 struct simple_attr *sattr;
160 unsigned long long data;
161 size_t bufsize;
162 ssize_t ret;
163
164 sattr = filp->private_data;
165 bufsize = strlen(buf) + 1;
166
167 if (sattr->set == NULL)
168 return (-EFAULT);
169
170 if (*ppos >= bufsize || write_size < 1)
171 return (-EINVAL);
172
173 mutex_lock(&sattr->mutex);
174
175 ret = kstrtoull(buf + *ppos, 0, &data);
176 if (ret)
177 goto unlock;
178
179 ret = sattr->set(sattr->data, data);
180 if (ret)
181 goto unlock;
182
183 ret = bufsize - *ppos;
184
185 unlock:
186 mutex_unlock(&sattr->mutex);
187 return (ret);
188 }
189