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 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 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 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 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