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/cdefs.h> 29 #include <sys/types.h> 30 #include <linux/fs.h> 31 32 MALLOC_DEFINE(M_LSATTR, "simple_attr", "Linux Simple Attribute File"); 33 34 struct simple_attr { 35 int (*get)(void *, uint64_t *); 36 int (*set)(void *, uint64_t); 37 void *data; 38 const char *fmt; 39 struct mutex mutex; 40 }; 41 42 /* 43 * simple_attr_open: open and populate simple attribute data 44 * 45 * @inode: file inode 46 * @filp: file pointer 47 * @get: ->get() for reading file data 48 * @set: ->set() for writing file data 49 * @fmt: format specifier for data returned by @get 50 * 51 * Memory allocate a simple_attr and appropriately initialize its members. 52 * The simple_attr must be stored in filp->private_data. 53 * Simple attr files do not support seeking. Open the file as nonseekable. 54 * 55 * Return value: simple attribute file descriptor 56 */ 57 int 58 simple_attr_open(struct inode *inode, struct file *filp, 59 int (*get)(void *, uint64_t *), int (*set)(void *, uint64_t), 60 const char *fmt) 61 { 62 struct simple_attr *sattr; 63 sattr = malloc(sizeof(*sattr), M_LSATTR, M_ZERO | M_NOWAIT); 64 if (sattr == NULL) 65 return (-ENOMEM); 66 67 sattr->get = get; 68 sattr->set = set; 69 sattr->data = inode->i_private; 70 sattr->fmt = fmt; 71 mutex_init(&sattr->mutex); 72 73 filp->private_data = (void *) sattr; 74 75 return (nonseekable_open(inode, filp)); 76 } 77 78 int 79 simple_attr_release(struct inode *inode, struct file *filp) 80 { 81 free(filp->private_data, M_LSATTR); 82 return (0); 83 } 84 85 /* 86 * simple_attr_read: read simple attr data and transfer into buffer 87 * 88 * @filp: file pointer 89 * @buf: kernel space buffer 90 * @read_size: number of bytes to be transferred 91 * @ppos: starting pointer position for transfer 92 * 93 * The simple_attr structure is stored in filp->private_data. 94 * ->get() retrieves raw file data. 95 * The ->fmt specifier can format this data to be human readable. 96 * This output is then transferred into the @buf buffer. 97 * 98 * Return value: 99 * On success, number of bytes transferred 100 * On failure, negative signed ERRNO 101 */ 102 ssize_t 103 simple_attr_read(struct file *filp, char *buf, size_t read_size, loff_t *ppos) 104 { 105 struct simple_attr *sattr; 106 uint64_t data; 107 ssize_t ret; 108 char prebuf[24]; 109 110 sattr = filp->private_data; 111 112 if (sattr->get == NULL) 113 return (-EFAULT); 114 115 mutex_lock(&sattr->mutex); 116 117 ret = sattr->get(sattr->data, &data); 118 if (ret) 119 goto unlock; 120 121 scnprintf(prebuf, sizeof(prebuf), sattr->fmt, data); 122 123 ret = strlen(prebuf) + 1; 124 if (*ppos >= ret || read_size < 1) { 125 ret = -EINVAL; 126 goto unlock; 127 } 128 129 read_size = min(ret - *ppos, read_size); 130 ret = strscpy(buf, prebuf + *ppos, read_size); 131 132 /* add 1 for null terminator */ 133 if (ret > 0) 134 ret += 1; 135 136 unlock: 137 mutex_unlock(&sattr->mutex); 138 return (ret); 139 } 140 141 /* 142 * simple_attr_write: write contents of buffer into simple attribute file 143 * 144 * @filp: file pointer 145 * @buf: kernel space buffer 146 * @write_size: number bytes to be transferred 147 * @ppos: starting pointer position for transfer 148 * 149 * The simple_attr structure is stored in filp->private_data. 150 * Convert the @buf string to unsigned long long. 151 * ->set() writes unsigned long long data into the simple attr file. 152 * 153 * Return value: 154 * On success, number of bytes written to simple attr 155 * On failure, negative signed ERRNO 156 */ 157 ssize_t 158 simple_attr_write(struct file *filp, const char *buf, size_t write_size, loff_t *ppos) 159 { 160 struct simple_attr *sattr; 161 unsigned long long data; 162 size_t bufsize; 163 ssize_t ret; 164 165 sattr = filp->private_data; 166 bufsize = strlen(buf) + 1; 167 168 if (sattr->set == NULL) 169 return (-EFAULT); 170 171 if (*ppos >= bufsize || write_size < 1) 172 return (-EINVAL); 173 174 mutex_lock(&sattr->mutex); 175 176 ret = kstrtoull(buf + *ppos, 0, &data); 177 if (ret) 178 goto unlock; 179 180 ret = sattr->set(sattr->data, data); 181 if (ret) 182 goto unlock; 183 184 ret = bufsize - *ppos; 185 186 unlock: 187 mutex_unlock(&sattr->mutex); 188 return (ret); 189 } 190