1 #include <linux/module.h> 2 #include <linux/moduleparam.h> 3 #include <linux/init.h> 4 #include <linux/kernel.h> /* printk() */ 5 #include <linux/slab.h> /* kmalloc() */ 6 #include <linux/fs.h> /* everything... */ 7 #include <linux/errno.h> /* error codes */ 8 #include <linux/types.h> /* size_t */ 9 #include <linux/fcntl.h> /* O_ACCMODE */ 10 #include <linux/cdev.h> 11 #include <asm/system.h> /* cli(), *_flags */ 12 #include <asm/uaccess.h> /* copy_*_user */ 13 #include "scull.h" /* local definitions */ 14 /* 15 * Our parameters which can be set at load time. 16 */ 17 //主设备号 18 int scull_major = SCULL_MAJOR; 19 //次设备号 20 int scull_minor = 0; 21 //请求连续设备编号数量 22 int scull_nr_devs = SCULL_NR_DEVS; /* number of bare scull devices */ 23 //量子大小 24 int scull_quantum = SCULL_QUANTUM; 25 //量子集大小 26 int scull_qset = SCULL_QSET; 27 module_param(scull_major, int, S_IRUGO); 28 module_param(scull_minor, int, S_IRUGO); 29 module_param(scull_nr_devs, int, S_IRUGO); 30 module_param(scull_quantum, int, S_IRUGO); 31 module_param(scull_qset, int, S_IRUGO); 32 struct scull_dev *scull_devices; /* allocated in scull_init_module */ 33 /* 34 * Empty out the scull device; must be called with the device 35 * semaphore held. 36 */ 37 /* 38 * 释放整个数据区，简单遍历列表并且释放它发现的任何量子和量子集。 39 * 在scull_open在文件为写而打开时调用。 40 * 调用这个函数时必须持有信号量。 41 */ 42 int scull_trim(struct scull_dev *dev) 43 { 44 struct scull_qset *next, *dptr; 45 //量子集大小 46 int qset = dev->qset; /* "dev" is not-null */ 47 int i; 48 for (dptr = dev->data; dptr; dptr = next) { /* all the list items */ 49 if (dptr->data) {//量子集中有数据 50 //遍历释放当前量子集中的每个量子，量子集大小为qset 51 for (i = 0; i < qset; i++) 52 kfree(dptr->data[i]); 53 //释放量子数组指针 54 kfree(dptr->data); 55 dptr->data = NULL; 56 } 57 //next获取下一个量子集，释放当前量子集 58 next = dptr->next; 59 kfree(dptr); 60 } 61 //清理struct scull_dev dev中的变量的值 62 dev->size = 0; 63 dev->quantum = scull_quantum; 64 dev->qset = scull_qset; 65 dev->data = NULL; 66 return 0; 67 } 68 /* 69 * Open and close 70 */ 71 int scull_open(struct inode *inode, struct file *filp) 72 { 73 struct scull_dev *dev; /* device information */ 74 dev = container_of(inode->i_cdev, struct scull_dev, cdev); 75 filp->private_data = dev; /* for other methods */ 76 /* now trim to 0 the length of the device if open was write-only */ 77 //文件以只读模式打开时，截断为0 78 if ( (filp->f_flags & O_ACCMODE) == O_WRONLY) { 79 if (down_interruptible(&dev->sem)) 80 return -ERESTARTSYS; 81 scull_trim(dev); /* ignore errors */ 82 up(&dev->sem); 83 } 84 return 0; /* success */ 85 } 86 int scull_release(struct inode *inode, struct file *filp) 87 { 88 return 0; 89 } 90 /* 91 * Follow the list 92 */ 93 //返回设备dev的第n个量子集的指针，量子集不够n个就申请新的 94 struct scull_qset *scull_follow(struct scull_dev *dev, int n) 95 { 96 //第一个量子集指针 97 struct scull_qset *qs = dev->data; 98 /* Allocate first qset explicitly if need be */ 99 // 如果当前设备还没有量子集，就显示分配第一个量子集 100 if (! qs) { 101 qs = dev->data = kmalloc(sizeof(struct scull_qset), GFP_KERNEL); 102 if (qs == NULL) 103 return NULL; /* Never mind */ 104 memset(qs, 0, sizeof(struct scull_qset)); 105 } 106 /* Then follow the list */ 107 // 遍历当前设备的量子集链表n步，量子集不够就申请新的 108 while (n--) { 109 if (!qs->next) { 110 qs->next = kmalloc(sizeof(struct scull_qset), GFP_KERNEL); 111 if (qs->next == NULL) 112 return NULL; /* Never mind */ 113 memset(qs->next, 0, sizeof(struct scull_qset)); 114 } 115 qs = qs->next; 116 continue; 117 } 118 return qs; 119 } 120 /* 121 * Data management: read and write 122 */ 123 ssize_t scull_read( struct file *filp, //设备对应的文件结构 124 char __user *buf, //读到用户空间 125 size_t count, //字节数 126 loff_t *f_pos) //要读的位置，在filp私有数据中的偏移 127 { 128 struct scull_dev *dev = filp->private_data; 129 struct scull_qset *dptr; /* the first listitem */ 130 //量子、量子集大小 131 int quantum = dev->quantum, qset = dev->qset; 132 //一个量子集的字节数 133 int itemsize = quantum * qset; /* how many bytes in the listitem */ 134 int item, s_pos, q_pos, rest; 135 ssize_t retval = 0; 136 if (down_interruptible(&dev->sem)) 137 return -ERESTARTSYS; 138 //要读的位置超过了数据总量 139 if (*f_pos >= dev->size) 140 goto out; 141 //要读的count超出了size，截断count 142 if (*f_pos + count > dev->size) 143 count = dev->size - *f_pos; 144 /* find listitem, qset index, and offset in the quantum */ 145 //在量子/量子集中定位读写位置：第几个量子集，中的第几个量子，在量子中偏移 146 //第几个量子集 147 item = (long)*f_pos / itemsize; 148 //在量子集中的偏移量 149 rest = (long)*f_pos % itemsize; 150 //第几个量子，在量子中的偏移 151 s_pos = rest / quantum; q_pos = rest % quantum; 152 /* follow the list up to the right position (defined elsewhere) */ 153 //读取要读的量子集的指针 154 dptr = scull_follow(dev, item); 155 //读取出错处理 156 if (dptr == NULL || !dptr->data || ! dptr->data[s_pos]) 157 goto out; /* don't fill holes */ 158 /* read only up to the end of this quantum */ 159 // 只在一个量子中读：如果count超出当前量子，截断count 160 if (count > quantum - q_pos) 161 count = quantum - q_pos; 162 // 将要读位置的内容复制count字节到用户空间buf中 163 if (copy_to_user(buf, dptr->data[s_pos] + q_pos, count)) { 164 retval = -EFAULT; 165 goto out; 166 } 167 *f_pos += count; 168 retval = count; 169 out: 170 up(&dev->sem); 171 return retval; 172 } 173 ssize_t scull_write(struct file *filp, const char __user *buf, size_t count, 174 loff_t *f_pos) 175 { 176 struct scull_dev *dev = filp->private_data; 177 struct scull_qset *dptr; 178 //量子、量子集大小 179 int quantum = dev->quantum, qset = dev->qset; 180 // 一个量子集总字节数 181 int itemsize = quantum * qset; 182 int item, s_pos, q_pos, rest; 183 ssize_t retval = -ENOMEM; /* value used in "goto out" statements */ 184 if (down_interruptible(&dev->sem)) 185 return -ERESTARTSYS; 186 /* find listitem, qset index and offset in the quantum */ 187 //第几个量子集 188 item = (long)*f_pos / itemsize; 189 //在该量子集中的偏移 190 rest = (long)*f_pos % itemsize; 191 //在该量子集中的第几个量子，在量子中的偏移 192 s_pos = rest / quantum; q_pos = rest % quantum; 193 /* follow the list up to the right position */ 194 //返回该量子集的指针 195 dptr = scull_follow(dev, item); 196 if (dptr == NULL) 197 goto out; 198 //如果该量子集数据为NULL，就申请一块新内存 199 if (!dptr->data) { 200 dptr->data = kmalloc(qset * sizeof(char *), GFP_KERNEL); 201 if (!dptr->data) 202 goto out; 203 memset(dptr->data, 0, qset * sizeof(char *)); 204 } 205 //如果第s_pos个量子是NULL，就申请一块新内存 206 if (!dptr->data[s_pos]) { 207 dptr->data[s_pos] = kmalloc(quantum, GFP_KERNEL); 208 if (!dptr->data[s_pos]) 209 goto out; 210 } 211 /* write only up to the end of this quantum */ 212 // 只在一个量子中写，如果count超出当前量子就截断 213 if (count > quantum - q_pos) 214 count = quantum - q_pos; 215 //从用户空间拷贝数据到内核空间，失败返回没有拷贝的字节数，成功返回0 216 if (copy_from_user(dptr->data[s_pos]+q_pos, buf, count)) { 217 retval = -EFAULT; 218 goto out; 219 } 220 *f_pos += count; 221 retval = count; 222 /* update the size */ 223 // 更新字节总数大小 224 if (dev->size < *f_pos) 225 dev->size = *f_pos; 226 out: 227 up(&dev->sem); 228 return retval; 229 } 230 231 struct file_operations scull_fops = { 232 .owner = THIS_MODULE, 233 .read = scull_read, 234 .write = scull_write, 235 .open = scull_open, 236 .release = scull_release, 237 }; 238 /* 239 * Finally, the module stuff 240 */ 241 /* 242 * The cleanup function is used to handle initialization failures as well. 243 * Thefore, it must be careful to work correctly even if some of the items 244 * have not been initialized 245 */ 246 void scull_cleanup_module(void) 247 { 248 int i; 249 //主次设备号合成一个dev_t结构，即设备编号 250 dev_t devno = MKDEV(scull_major, scull_minor); 251 /* Get rid of our char dev entries */ 252 if (scull_devices) { 253 //便利释放每个设备的数据区 254 for (i = 0; i < scull_nr_devs; i++) { 255 //释放数据区 256 scull_trim(scull_devices + i); 257 //移除cdev 258 cdev_del(&scull_devices[i].cdev); 259 } 260 //释放scull_devices本身 261 kfree(scull_devices); 262 } 263 /* cleanup_module is never called if registering failed */ 264 unregister_chrdev_region(devno, scull_nr_devs); 265 } 266 267 /* 268 * Set up the char_dev structure for this device. 269 */ 270 // 建立char_dev结构 271 static void scull_setup_cdev(struct scull_dev *dev, int index) 272 { 273 int err, devno = MKDEV(scull_major, scull_minor + index); 274 275 cdev_init(&dev->cdev, &scull_fops); 276 dev->cdev.owner = THIS_MODULE; 277 // dev->cdev.ops = &scull_fops; 278 //添加字符设备dev->cdev,立即生效 279 err = cdev_add (&dev->cdev, devno, 1); 280 /* Fail gracefully if need be */ 281 if (err) 282 printk(KERN_NOTICE "Error %d adding scull%d", err, index); 283 } 284 285 int scull_init_module(void) 286 { 287 int result, i; 288 dev_t dev = 0; 289 /* 290 * Get a range of minor numbers to work with, asking for a dynamic 291 * major unless directed otherwise at load time. 292 */ 293 //申请设备编号，若在加载时没有指定主设备号就动态分配 294 if (scull_major) { 295 dev = MKDEV(scull_major, scull_minor); 296 result = register_chrdev_region(dev, scull_nr_devs, "scull"); 297 } else { 298 result = alloc_chrdev_region(&dev, scull_minor, scull_nr_devs, 299 "scull"); 300 scull_major = MAJOR(dev); 301 } 302 if (result < 0) { 303 printk(KERN_WARNING "scull: can't get major %d\n", scull_major); 304 return result; 305 } 306 /* 307 * allocate the devices -- we can't have them static, as the number 308 * can be specified at load time 309 */ 310 //给scull_dev对象申请内存 311 scull_devices = kmalloc(scull_nr_devs * sizeof(struct scull_dev), GFP_KERNEL); 312 if (!scull_devices) { 313 result = -ENOMEM; 314 goto fail; /* Make this more graceful */ 315 } 316 memset(scull_devices, 0, scull_nr_devs * sizeof(struct scull_dev)); 317 /* Initialize each device. */ 318 for (i = 0; i < scull_nr_devs; i++) { 319 scull_devices[i].quantum = scull_quantum; 320 scull_devices[i].qset = scull_qset; 321 //初始化互斥锁，把信号量sem置为1 322 sema_init(&scull_devices[i].sem, 1); 323 //init_MUTEX(&scull_devices[i].sem); 324 //建立char_dev结构 325 scull_setup_cdev(&scull_devices[i], i); 326 } 327 return 0; /* succeed */ 328 fail: 329 scull_cleanup_module(); 330 return result; 331 } 332 module_init(scull_init_module); 333 module_exit(scull_cleanup_module); 334 MODULE_AUTHOR("Tekkamanninja"); 335 MODULE_LICENSE("Dual BSD/GPL");