1 // SPDX-License-Identifier: GPL-2.0-only 2 /* 3 * Sample kfifo byte stream implementation 4 * 5 * Copyright (C) 2010 Stefani Seibold <stefani@seibold.net> 6 */ 7 8 #include <linux/init.h> 9 #include <linux/module.h> 10 #include <linux/proc_fs.h> 11 #include <linux/mutex.h> 12 #include <linux/kfifo.h> 13 14 /* 15 * This module shows how to create a byte stream fifo. 16 */ 17 18 /* fifo size in elements (bytes) */ 19 #define FIFO_SIZE 32 20 21 /* name of the proc entry */ 22 #define PROC_FIFO "bytestream-fifo" 23 24 /* lock for procfs read access */ 25 static DEFINE_MUTEX(read_access); 26 27 /* lock for procfs write access */ 28 static DEFINE_MUTEX(write_access); 29 30 /* 31 * define DYNAMIC in this example for a dynamically allocated fifo. 32 * 33 * Otherwise the fifo storage will be a part of the fifo structure. 34 */ 35 #if 0 36 #define DYNAMIC 37 #endif 38 39 #ifdef DYNAMIC 40 static struct kfifo test; 41 #else 42 static DECLARE_KFIFO(test, unsigned char, FIFO_SIZE); 43 #endif 44 45 static const unsigned char expected_result[FIFO_SIZE] = { 46 3, 4, 5, 6, 7, 8, 9, 0, 47 1, 20, 21, 22, 23, 24, 25, 26, 48 27, 28, 29, 30, 31, 32, 33, 34, 49 35, 36, 37, 38, 39, 40, 41, 42, 50 }; 51 52 static int __init testfunc(void) 53 { 54 unsigned char buf[6]; 55 unsigned char i, j; 56 unsigned int ret; 57 58 printk(KERN_INFO "byte stream fifo test start\n"); 59 60 /* put string into the fifo */ 61 kfifo_in(&test, "hello", 5); 62 63 /* put values into the fifo */ 64 for (i = 0; i != 10; i++) 65 kfifo_put(&test, i); 66 67 /* show the number of used elements */ 68 printk(KERN_INFO "fifo len: %u\n", kfifo_len(&test)); 69 70 /* get max of 5 bytes from the fifo */ 71 i = kfifo_out(&test, buf, 5); 72 printk(KERN_INFO "buf: %.*s\n", i, buf); 73 74 /* get max of 2 elements from the fifo */ 75 ret = kfifo_out(&test, buf, 2); 76 printk(KERN_INFO "ret: %d\n", ret); 77 /* and put it back to the end of the fifo */ 78 ret = kfifo_in(&test, buf, ret); 79 printk(KERN_INFO "ret: %d\n", ret); 80 81 /* skip first element of the fifo */ 82 printk(KERN_INFO "skip 1st element\n"); 83 kfifo_skip(&test); 84 85 /* put values into the fifo until is full */ 86 for (i = 20; kfifo_put(&test, i); i++) 87 ; 88 89 printk(KERN_INFO "queue len: %u\n", kfifo_len(&test)); 90 91 /* show the first value without removing from the fifo */ 92 if (kfifo_peek(&test, &i)) 93 printk(KERN_INFO "%d\n", i); 94 95 /* check the correctness of all values in the fifo */ 96 j = 0; 97 while (kfifo_get(&test, &i)) { 98 printk(KERN_INFO "item = %d\n", i); 99 if (i != expected_result[j++]) { 100 printk(KERN_WARNING "value mismatch: test failed\n"); 101 return -EIO; 102 } 103 } 104 if (j != ARRAY_SIZE(expected_result)) { 105 printk(KERN_WARNING "size mismatch: test failed\n"); 106 return -EIO; 107 } 108 printk(KERN_INFO "test passed\n"); 109 110 return 0; 111 } 112 113 static ssize_t fifo_write(struct file *file, const char __user *buf, 114 size_t count, loff_t *ppos) 115 { 116 int ret; 117 unsigned int copied; 118 119 if (mutex_lock_interruptible(&write_access)) 120 return -ERESTARTSYS; 121 122 ret = kfifo_from_user(&test, buf, count, &copied); 123 124 mutex_unlock(&write_access); 125 if (ret) 126 return ret; 127 128 return copied; 129 } 130 131 static ssize_t fifo_read(struct file *file, char __user *buf, 132 size_t count, loff_t *ppos) 133 { 134 int ret; 135 unsigned int copied; 136 137 if (mutex_lock_interruptible(&read_access)) 138 return -ERESTARTSYS; 139 140 ret = kfifo_to_user(&test, buf, count, &copied); 141 142 mutex_unlock(&read_access); 143 if (ret) 144 return ret; 145 146 return copied; 147 } 148 149 static const struct proc_ops fifo_proc_ops = { 150 .proc_read = fifo_read, 151 .proc_write = fifo_write, 152 .proc_lseek = noop_llseek, 153 }; 154 155 static int __init example_init(void) 156 { 157 #ifdef DYNAMIC 158 int ret; 159 160 ret = kfifo_alloc(&test, FIFO_SIZE, GFP_KERNEL); 161 if (ret) { 162 printk(KERN_ERR "error kfifo_alloc\n"); 163 return ret; 164 } 165 #else 166 INIT_KFIFO(test); 167 #endif 168 if (testfunc() < 0) { 169 #ifdef DYNAMIC 170 kfifo_free(&test); 171 #endif 172 return -EIO; 173 } 174 175 if (proc_create(PROC_FIFO, 0, NULL, &fifo_proc_ops) == NULL) { 176 #ifdef DYNAMIC 177 kfifo_free(&test); 178 #endif 179 return -ENOMEM; 180 } 181 return 0; 182 } 183 184 static void __exit example_exit(void) 185 { 186 remove_proc_entry(PROC_FIFO, NULL); 187 #ifdef DYNAMIC 188 kfifo_free(&test); 189 #endif 190 } 191 192 module_init(example_init); 193 module_exit(example_exit); 194 MODULE_LICENSE("GPL"); 195 MODULE_AUTHOR("Stefani Seibold <stefani@seibold.net>"); 196