char_dev.c裡的中文注釋，僅代表個人理解，僅供參考。如有錯誤之處，請指出，謝謝！
1 /*
2 * linux/fs/char_dev.c
3 *
4 * Copyright (C) 1991, 1992 Linus Torvalds
5 */
6
7 #include <linux/init.h>
8 #include <linux/fs.h>
9 #include <linux/kdev_t.h>
10 #include <linux/slab.h>
11 #include <linux/string.h>
12
13 #include <linux/major.h>
14 #include <linux/errno.h>
15 #include <linux/module.h>
16 #include <linux/smp_lock.h>
17 #include <linux/seq_file.h>
18
19 #include <linux/kobject.h>
20 #include <linux/kobj_map.h>
21 #include <linux/cdev.h>
22 #include <linux/mutex.h>
23 #include <linux/backing-dev.h>
24
25 #ifdef CONFIG_KMOD
26 #include <linux/kmod.h>
27 #endif
28 #include "internal.h"
29
30 /*
31 * capabilities for /dev/mem, /dev/kmem and similar directly mappable character
32 * devices
33 * - permits shared-mmap for read, write and/or exec
34 * - does not permit private mmap in NOMMU mode (can't do COW)
35 * - no readahead or I/O queue unplugging required
36 */
37
38 struct backing_dev_info directly_mappable_cdev_bdi = {
39 .capabilities = (
40 #ifdef CONFIG_MMU
41 /* permit private copies of the data to be taken */
42 BDI_CAP_MAP_COPY |
43 #endif
44 /* permit direct mmap, for read, write or exec */
45 BDI_CAP_MAP_DIRECT |
46 BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP),
47 };
48
49 static struct kobj_map *cdev_map;
50
51 static DEFINE_MUTEX(chrdevs_lock);
52
53 static struct char_device_struct {
54 struct char_device_struct *next;
55 unsigned int major;
56 unsigned int baseminor;
57 int minorct;
58 char name[64];
59 struct file_operations *fops;
60 struct cdev *cdev;
61 /* will die */
62 } *chrdevs[CHRDEV_MAJOR_HASH_SIZE];
63
64 /* index in the above */
65 static inline int major_to_index(int major)
66 {
67 /* [CGW]: 根據主設備號，轉換成對應的索引
68 * 即主設備號就是索引號
69 */
70 return major % CHRDEV_MAJOR_HASH_SIZE;
71 }
72
73 #ifdef CONFIG_PROC_FS
74
75 void chrdev_show(struct seq_file *f, off_t offset)
76 {
77 struct char_device_struct *cd;
78 /* [CGW]: 根據offset (相當於索引)，找到對應設備 */
79 if (offset < CHRDEV_MAJOR_HASH_SIZE) {
80 /* [CGW]: 上鎖 */
81 mutex_lock(&chrdevs_lock);
82 /* [CGW]: 打印該設備項下鏈表中所有節點的主設備號，和設備名 */
83 for (cd = chrdevs[offset]; cd; cd = cd->next)
84 seq_printf(f, "%3d %s\n", cd->major, cd->name);
85 /* [CGW]: 解鎖 */
86 mutex_unlock(&chrdevs_lock);
87 }
88 }
89
90 #endif /* CONFIG_PROC_FS */
91
92 /*
93 * Register a single major with a specified minor range.
94 *
95 * If major == 0 this functions will dynamically allocate a major and return
96 * its number.
97 *
98 * If major > 0 this function will attempt to reserve the passed range of
99 * minors and will return zero on success.
100 *
101 * Returns a -ve errno on failure.
102 */
103
104 static struct char_device_struct *
105 __register_chrdev_region(unsigned int major, unsigned int baseminor,
106 int minorct, const char *name)
107
108 {
109 struct char_device_struct *cd, **cp;
110 int ret = 0;
111 int i;
112
113 /* [cgw]: 分配一塊char_device_struct大小的內存塊 */
114 cd = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);
115 /* [cgw]: 分配失敗 */
116 if (cd == NULL)
117 return ERR_PTR(-ENOMEM);
118 /*[cgw]: 上鎖，進入臨界區*/
119 mutex_lock(&chrdevs_lock);
120 /* temporary */
121 /*[cgw]: 如果主設備號為0，則從最大的設備號開始，往下查找第一個未被
122 *注冊的設備
123 */
124 if (major == 0) {
125 /*[cgw]: 從大到小開始查找*/
126 for (i = ARRAY_SIZE(chrdevs)-1; i > 0; i--) {
127 /* [cgw]: 找到第一個未被注冊的設備 */
128 if (chrdevs[i] == NULL)
129 break;
130 }
131 /* [cgw]:未找到空位 */
132 if (i == 0) {
133 ret = -EBUSY;
134 goto out;
135 }
136 /* [cgw]: 以該空位的序號為主設備號 */
137 major = i;
138 ret = major;
139 }
140
141 /* [cgw]: 手工分配一個主設備號，和次設備號基址 */
142 cd->major = major;
143 /* [cgw]: 手工分配次設備號基址 */
144 cd->baseminor = baseminor;
145 /* [cgw]: 分配minorct個次設備號 */
146 cd->minorct = minorct;
147 /* [cgw]: 分配設備名 */
148 strncpy(cd->name,name, 64);
149 /* [cgw]: 找到主設備號在設備列表中的索引 */
150 i = major_to_index(major);
151 /* [cgw]: 當前分配的設備號比較設備列表，判斷該設備號是否
152 * 合法
153 */
154 for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
155 /* [cgw]: 當前分配的主設備號，小於該主設備號索引對應的，設備列表
156 * 中的主設備號，合法
157 * 這個裡有點不解，從i = major_to_index(major);看出，主設備號和該主
158 * 設備號對應的索引是相等的，為什麼(*cp)->major > major是合法呢
159 */
160 if ((*cp)->major > major ||
161 /* [cgw]: 當前分配的主設備號，等於該主設備號索引對應的，設備列表
162 * 中的主設備號，並且符合以下條件之一，當前分配的次設備號，等於
163 * 小於該主設備號索引對應的，設備列表中的次設備號。或者，當前分
164 * 配的次設備號，小於該主設備號索引對應的，設備列表中的次設備基
165 * 址以後minorct個次設備號
166 */
167 ((*cp)->major == major &&
168 (((*cp)->baseminor >= baseminor) ||
169 ((*cp)->baseminor + (*cp)->minorct > baseminor))))
170 break;
171 /* Check for overlapping minor ranges. */
172 /* [cgw]: 當前分配的主設備號，等於該主設備號索引對應的，設備列表
173 * 中的主設備號，判斷次設備號是否在范圍內
174 */
175 if (*cp && (*cp)->major == major) {
176 int old_min = (*cp)->baseminor;
177 int old_max = (*cp)->baseminor + (*cp)->minorct - 1;
178 int new_min = baseminor;
179 int new_max = baseminor + minorct - 1;
180
181 /* New driver overlaps from the left. */
182 if (new_max >= old_min && new_max <= old_max) {
183 ret = -EBUSY;
184 goto out;
185 }
186
187 /* New driver overlaps from the right. */
188 if (new_min <= old_max && new_min >= old_min) {
189 ret = -EBUSY;
190 goto out;
191 }
192 }
193
194 /* [cgw]: 新加入的設備， 添加到該主設備號鏈表 */
195 cd->next = *cp;
196 /* [cgw]: 設備列表指針指向新加入設備*/
197 *cp = cd;
198 /* [cgw]: 解鎖，退出臨界區*/
199 mutex_unlock(&chrdevs_lock);
200 return cd;
201 out:
202
203 /* [cgw]: 解鎖，退出臨界區*/
204 mutex_unlock(&chrdevs_lock);
205 /* [cgw]: 釋放為新設備創建的內存*/
206 kfree(cd);
207 return ERR_PTR(ret);
208 }
209
210 static struct char_device_struct *
211 __unregister_chrdev_region(unsigned major, unsigned baseminor, int minorct)
212
213 {
214 struct char_device_struct *cd = NULL, **cp;
215 /* [CGW]: 根據主設備號，找出該主設備號所在列表中的索引*/
216 int i = major_to_index(major);
217 /* [CGW]: 上鎖，進入臨界區 */
218 mutex_lock(&chrdevs_lock);
219 /* [CGW]: 根據索引，找出該主設備號所在列表項 */
220 for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
221 /* [CGW]:主設備號所在列表項中, 在主設備號對應的鏈表中，查找判斷該主設備號，
222 * 次設備號基址，次設備號個數是否已經被注冊
223 */
224 if ((*cp)->major == major &&
225 (*cp)->baseminor == baseminor &&
226 (*cp)->minorct == minorct)
227 /* [CGW]: 已經被注冊，停止查找 */
228 break;
229 /* [CGW]: 主設備號所在鏈表中的節點
230 * (注意: 設備列表中,每個設備號都對應一個鏈表,該鏈表用於存放此設備號)
231 */
232 if (*cp) {
233 /* [CGW]: 取出該節點 */
234 cd = *cp;
235 /* [CGW]: 更新cp，指向下一個節點*/
236 *cp = cd->next;
237 }
238
239 /* [CGW]: 解鎖，退出臨界區 */
240 mutex_unlock(&chrdevs_lock);
241 /* [CGW]: 返回該設備(節點) */
242 return cd;
243
244 }
245
246
247
248
249 /**
250 * register_chrdev_region() - register a range of device numbers
251 * @from: the first in the desired range of device numbers; must include
252 * the major number.
253 * @count: the number of consecutive device numbers required
254 * @name: the name of the device or driver.
255 *
256 * Return value is zero on success, a negative error code on failure.
257 */
258
259 int register_chrdev_region(dev_t from, unsigned count, const char *name)
260
261 {
262 struct char_device_struct *cd;
263 dev_t to = from + count;
264 dev_t n, next;
265 /* [CGW]: 分配count個連續的設備 */
266 for (n = from; n < to; n = next) {
267 /* [CGW]: 主設備號+1遞增 */
268 next = MKDEV(MAJOR(n)+1, 0);
269 if (next > to)
270 next = to;
271
272 /* [CGW]: 根據主、次設備號基址，分配next - n個連續次設備號的設備，
273 * 並根據主設備號分配設備名
274 * 如果MINOR(n)為0，next-n的值應恆為256，未驗證!!!
275 */
276 cd = __register_chrdev_region(MAJOR(n), MINOR(n),
277 next - n, name);
278 /* [CGW]: 分配失敗 */
279 if (IS_ERR(cd))
280 goto fail;
281 }
282 return 0;
283
284 fail:
285
286 /* [CGW]: 當前分配到了第n個設備就失敗了*/
287 to = n;
288 /* [CGW]: 注銷剛剛分配的所有設備 */
289 for (n = from; n < to; n = next) {
290 next = MKDEV(MAJOR(n)+1, 0);
291 /* [CGW]: 對應的內存空間 */
292 kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
293 }
294
295 /* [CGW]: 返回這個分配失敗的設備指針 */
296 return PTR_ERR(cd);
297 }
298
299 /**
300 * alloc_chrdev_region() - register a range of char device numbers
301 * @dev: output parameter for first assigned number
302 * @baseminor: first of the requested range of minor numbers
303 * @count: the number of minor numbers required
304 * @name: the name of the associated device or driver
305 *
306 * Allocates a range of char device numbers. The major number will be
307 * chosen dynamically, and returned (along with the first minor number)
308 * in @dev. Returns zero or a negative error code.
309 */
310 int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count,
311 const char *name)
312
313 {
314 struct char_device_struct *cd;
315 /* [CGW]: 自動分配一個設備，因為主設備號為0
316 * 以baseminor為基址，分配count個次設備號
317 */
318 cd = __register_chrdev_region(0, baseminor, count, name);
319 /* [CGW]: 分配失敗 */
320 if (IS_ERR(cd))
321 return PTR_ERR(cd);
322 /* [CGW]: 返回設備號 */
323 *dev = MKDEV(cd->major, cd->baseminor);
324 return 0;
325 }
326
327 /**
328 * register_chrdev() - Register a major number for character devices.
329 * @major: major device number or 0 for dynamic allocation
330 * @name: name of this range of devices
331 * @fops: file operations associated with this devices
332 *
333 * If @major == 0 this functions will dynamically allocate a major and return
334 * its number.
335 *
336 * If @major > 0 this function will attempt to reserve a device with the given
337 * major number and will return zero on success.
338 *
339 * Returns a -ve errno on failure.
340 *
341 * The name of this device has nothing to do with the name of the device in
342 * /dev. It only helps to keep track of the different owners of devices. If
343 * your module name has only one type of devices it's ok to use e.g. the name
344 * of the module here.
345 *
346 * This function registers a range of 256 minor numbers. The first minor number
347 * is 0.
348 */
349
350 int register_chrdev(unsigned int major, const char *name,
351 const struct file_operations *fops)
352
353 {
354 struct char_device_struct *cd;
355 struct cdev *cdev;
356 char *s;
357 int err = -ENOMEM;
358
359 /* [cgw]: 分配一個設備，次設備號為0~255 */
360 cd = __register_chrdev_region(major, 0, 256, name);
361 if (IS_ERR(cd))
362 return PTR_ERR(cd);
363 /* [cgw]:分配一個cdev結構體 */
364 cdev = cdev_alloc();
365 if (!cdev)
366 goto out2;
367
368 cdev->owner = fops->owner;
369 cdev->ops = fops;
370
371 /* [cgw]: 設置kobject的名字 */
372 kobject_set_name(&cdev->kobj, "%s", name);
373 /* [cgw]: 把kobject的名字kobj->name中的'/'替換成'!' */
374 for (s = strchr(kobject_name(&cdev->kobj),'/'); s; s = strchr(s, '/'))
375 *s = '!';
376
377 /* [cgw]: 添加一個字符設備到系統*/
378 err = cdev_add(cdev, MKDEV(cd->major, 0), 256);
379 if (err)
380 goto out;
381
382 /* [cgw]: 設置char_device_struct中的cdev指針 */
383 cd->cdev = cdev;
384
385 return major ? 0 : cd->major;
386
387 out:
388 /* [cgw]: kobect 引用計數-1 */
389 kobject_put(&cdev->kobj);
390
391 out2:
392 /* [cgw]: 釋放剛注冊的設備 */
393 kfree(__unregister_chrdev_region(cd->major, 0, 256));
394 return err;
395 }
396
397 /**
398 * unregister_chrdev_region() - return a range of device numbers
399 * @from: the first in the range of numbers to unregister
400 * @count: the number of device numbers to unregister
401 *
402 * This function will unregister a range of @count device numbers,
403 * starting with @from. The caller should normally be the one who
404 * allocated those numbers in the first place...
405 */
406
407 void unregister_chrdev_region(dev_t from, unsigned count)
408 {
409 dev_t to = from + count;
410 dev_t n, next;
411
412 /* [CGW]: 注銷所有從from到to的count個設備 */
413 for (n = from; n < to; n = next) {
414 /* [CGW]: 查找下一設備號*/
415 next = MKDEV(MAJOR(n)+1, 0);
416 if (next > to)
417 next = to;
418 /* [CGW]: 注銷所有剛才注冊的設備 */
419 kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
420 }
421 }
422
423
424 int unregister_chrdev(unsigned int major, const char *name)
425 {
426 struct char_device_struct *cd;
427 /* [CGW]: 根據主設備號，找到對應設備列表項 */
428 cd = __unregister_chrdev_region(major, 0, 256);
429 /* [CGW]: 該設備項有效，並且被注冊 */
430 if (cd && cd->cdev)
431 /* [CGW]: 注銷該設備 */
432 cdev_del(cd->cdev);
433 /* [CGW]: 釋放該設備占用的內存空間 */
434 kfree(cd);
435
436 return 0;
437 }
438
439 static DEFINE_SPINLOCK(cdev_lock);
440
441 static struct kobject *cdev_get(struct cdev *p)
442 {
443 struct module *owner = p->owner;
444 struct kobject *kobj;
445 /* [cgw]:cdev_get uses try_module_get to attempt to increment that module's
446 * usage count. If that operation succeeds, kobject_get is used to increment the
447 * kobject's reference count as well---<Linux Device Drivers>
448 * try_module_get(owner)增加owner (THIS_MODULE)引用計數
449 */
450 /* [cgw]: module使用計數+1 */
451 if (owner && !try_module_get(owner))
452 return NULL;
453 /* [cgw]: kobj引用計數+1 */
454 kobj = kobject_get(&p->kobj);
455 /* [cgw]: kobj指針返回失敗 */
456 if (!kobj)
457 /* [cgw]: module使用計數-1 */
458 module_put(owner);
459
460 return kobj;
461 }
462
463 void cdev_put(struct cdev *p)
464 {
465 /* [cgw]: cdev指針不為空 */
466 if (p) {
467 /* [cgw]: 獲得模塊指針 */
468 struct module *owner = p->owner;
469 /* [cgw]: kobj引用計數-1 */
470 kobject_put(&p->kobj);
471 /* [cgw]: module使用計數-1 */
472 module_put(owner);
473 }
474 }
475
476 /*
477 * Called every time a character special file is opened
478 */
479 int chrdev_open(struct inode * inode, struct file * filp)
480 {
481 struct cdev *p;
482 struct cdev *new = NULL;
483 int ret = 0;
484
485 /* [cgw]: 進入臨界區 */
486 spin_lock(&cdev_lock);
487 /* [cgw]: 從inode中得到一個字符設備cdev指針 */
488 p = inode->i_cdev;
489 /* [cgw]: struct cdev指針為空 */
490 if (!p) {
491 struct kobject *kobj;
492 int idx;
493 /* [cgw]: 進入臨界區 */
494 spin_unlock(&cdev_lock);
495 /* [cgw]: 看看cdev_map的probes[inode->i_rdev]鏈表是否有inode->i_rdev這個設備
496 * 並返回這個設備的kobj
497 */
498 kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
499 /* [cgw]: kobj為空，錯誤 */
500 if (!kobj)
501 return -ENXIO;
502 /* [cgw]: 根據返回的kobj，找出包含這個kobj的struct cdev指針 */
503 new = container_of(kobj, struct cdev, kobj);
504 /* [cgw]: 進入臨界區 */
505 spin_lock(&cdev_lock);
506 /* [cgw]: 從inode中得到一個字符設備cdev指針 */
507 p = inode->i_cdev;
508 /* [cgw]: struct cdev指針為空 */
509 if (!p) {
510 /* [cgw]: 把這個struct cdev指針填裝到inode->i_cdev */
511 inode->i_cdev = p = new;
512 /* [cgw]: 記錄對應的索引 */
513 inode->i_cindex = idx;
514 /* [cgw]: 把inode->i_devices插入到p->list */
515 list_add(&inode->i_devices, &p->list);
516 /* [cgw]: 清除new指針 */
517 new = NULL;
518 /* [cgw]: 返回cdev中kobj指針為空，錯誤 */
519 } else if (!cdev_get(p))
520 ret = -ENXIO;
521 /* [cgw]: 返回cdev中kobj指針為空，錯誤 */
522 } else if (!cdev_get(p))
523 ret = -ENXIO;
524 /* [cgw]: 退出臨界區 */
525 spin_unlock(&cdev_lock);
526 /* [cgw]: 實際上是cdev->kobj引用計數-1，module使用計數-1 */
527 cdev_put(new);
528 if (ret)
529 return ret;
530 /* [cgw]: module使用計數+1，並返回cdev->ops指針 */
531 filp->f_op = fops_get(p->ops);
532 /* [cgw]: filp->f_op指針為空，失敗 */
533 if (!filp->f_op) {
534 /* [cgw]: 實際上是cdev->kobj引用計數-1，module使用計數-1 */
535 cdev_put(p);
536 return -ENXIO;
537 }
538 /* [cgw]: 調用filp->f_op->open，打開的是用戶驅動程序中定義的
539 * file_operations中的open函數
540 */
541 if (filp->f_op->open) {
542 /* [cgw]: 上鎖 */
543 lock_kernel();
544 /* [cgw]: 調用filp->f_op->open */
545 ret = filp->f_op->open(inode,filp);
546 /* [cgw]: 解鎖 */
547 unlock_kernel();
548 }
549 /* [cgw]: 調用filp->f_op->open失敗 */
550 if (ret)
551 /* [cgw]: 實際上是cdev->kobj引用計數-1，module使用計數-1 */
552 cdev_put(p);
553
554 return ret;
555 }
556
557 void cd_forget(struct inode *inode)
558 {
559 /* [cgw]: 進入臨界區 */
560 spin_lock(&cdev_lock);
561 /* [cgw]: 從鏈表刪除一個inode->i_devices節點，
562 * 並重新初始化這個鏈表
563 */
564 list_del_init(&inode->i_devices);
565 /* [cgw]: inode->i_cdev指針清0 */
566 inode->i_cdev = NULL;
567 /* [cgw]: 退出臨界區 */
568 spin_unlock(&cdev_lock);
569 }
570
571 static void cdev_purge(struct cdev *cdev)
572 {
573 /* [cgw]: 進入臨界區 */
574 spin_lock(&cdev_lock);
575 /* [cgw]: 測試cdev->list這個鏈表是否為空
576 *
577 */
578 while (!list_empty(&cdev->list)) {
579 struct inode *inode;
580 /* [cgw]: 找出包含cdev->list的struct inode結構體的指針 */
581 inode = container_of(cdev->list.next, struct inode, i_devices);
582 /* [cgw]: 從鏈表刪除一個inode->i_devices節點，
583 * 並重新初始化這個鏈表
584 */
585 list_del_init(&inode->i_devices);
586 /* [cgw]: inode->i_cdev指針清0 */
587 inode->i_cdev = NULL;
588 }
589 /* [cgw]: 退出臨界區 */
590 spin_unlock(&cdev_lock);
591 }
592
593 /*
594 * Dummy default file-operations: the only thing this does
595 * is contain the open that then fills in the correct operations
596 * depending on the special file...
597 */
598
599 const struct file_operations def_chr_fops = {
600 .open = chrdev_open,
601 };
602 static struct kobject *exact_match(dev_t dev, int *part, void *data)
603 {
604 struct cdev *p = data;
605 /* [cgw]: 返回cdev中kobj成員指針 */
606 return &p->kobj;
607 }
608
609 static int exact_lock(dev_t dev, void *data)
610 {
611 struct cdev *p = data;
612 /* [cgw]: data中kobj引用計數+1，並返回kobj指針 */
613 return cdev_get(p) ? 0 : -1;
614 }
615
616 /**
617 * cdev_add() - add a char device to the system
618 * @p: the cdev structure for the device
619 * @dev: the first device number for which this device is responsible
620 * @count: the number of consecutive minor numbers corresponding to this
621 * device
622 *
623 * cdev_add() adds the device represented by @p to the system, making it
624 * live immediately. A negative error code is returned on failure.
625 */
626
627 int cdev_add(struct cdev *p, dev_t dev, unsigned count)
628 {
629 /* [cgw]: 分配一個dev設備號給p->dev */
630 p->dev = dev;
631 /* [cgw]: 分配count個連續的次設備號
632 * 這裡實際是分配count設備，只是次設備號不一樣，主設備號都一樣
633 */
634 p->count = count;
635 /* [cgw]: 把新加入的設備填裝到一個probe結構，並把這個probe插入到
636 * 對應probes[MAJOR(dev)]鏈表，即probes[]中每一個元素都是一個鏈表
637 */
638 return kobj_map(cdev_map, dev, count, NULL, exact_match, exact_lock, p);
639 }
640
641 static void cdev_unmap(dev_t dev, unsigned count)
642 {
643 /* [cgw]: 從probes[MAJOR(dev)]鏈表中刪除一個節點(probe) */
644 kobj_unmap(cdev_map, dev, count);
645 }
646
647 /**
648 * cdev_del() - remove a cdev from the system
649 * @p: the cdev structure to be removed
650 *
651 * cdev_del() removes @p from the system, possibly freeing the structure
652 * itself.
653 */
654
655 void cdev_del(struct cdev *p)
656 {
657 /* [cgw]: 從probes[MAJOR(p->dev)]鏈表中刪除一個節點(probe)
658 *
659 */
660 cdev_unmap(p->dev, p->count);
661 /* [cgw]: kobj引用計數-1 */
662 kobject_put(&p->kobj);
663 }
664
665 static void cdev_default_release(struct kobject *kobj)
666 {
667 /* [cgw]: 找到包含kobj的結構體struct cdev的指針 */
668 struct cdev *p = container_of(kobj, struct cdev, kobj);
669 /* [cgw]: 從cdev->list鏈表中刪除cdev */
670 cdev_purge(p);
671 }
672
673 static void cdev_dynamic_release(struct kobject *kobj)
674 {
675 /* [cgw]: 找到包含kobj的結構體struct cdev的指針 */
676 struct cdev *p = container_of(kobj, struct cdev, kobj);
677 /* [cgw]: 從cdev->list鏈表中刪除cdev */
678 cdev_purge(p);
679 /* [cgw]: 釋放這個cdev的內存空間 */
680 kfree(p);
681 }
682
683 static struct kobj_type ktype_cdev_default = {
684 .release = cdev_default_release,
685 };
686
687 static struct kobj_type ktype_cdev_dynamic = {
688 .release = cdev_dynamic_release,
689 };
690
691 /**
692 * cdev_alloc() - allocate a cdev structure
693 *
694 * Allocates and returns a cdev structure, or NULL on failure.
695 */
696 struct cdev *cdev_alloc(void)
697 {
698 /* [cgw]: 分配一個cdev結構體 */
699 struct cdev *p = kzalloc(sizeof(struct cdev), GFP_KERNEL);
700
701 /* [cgw]: 分配cdev結構體成功 */
702 if (p) {
703 /* [cgw]: 分配一個kobj.ktype結構體，指向&ktype_cdev_dynamic
704 * 為這個驅動制定一個統一的行為，提供釋放kobj的方法
705 */
706 p->kobj.ktype = &ktype_cdev_dynamic;
707 /* [cgw]: 初始化鏈表，把這個cdev插入鏈表頭 */
708 INIT_LIST_HEAD(&p->list);
709 /* [cgw]: 初始化kobject，每個對象都有一個kobject */
710 kobject_init(&p->kobj);
711 }
712 return p;
713 }
714
715 /**
716 * cdev_init() - initialize a cdev structure
717 * @cdev: the structure to initialize
718 * @fops: the file_operations for this device
719 *
720 * Initializes @cdev, remembering @fops, making it ready to add to the
721 * system with cdev_add().
722 */
723 void cdev_init(struct cdev *cdev, const struct file_operations *fops)
724 {
725 /* [cgw]: cdev結構體清零 */
726 memset(cdev, 0, sizeof *cdev);
727 /* [cgw]: 初始化鏈表，把這個cdev插入鏈表頭 */
728 INIT_LIST_HEAD(&cdev->list);
729 /* [cgw]: 分配一個kobj.ktype結構體，指向&ktype_cdev_default
730 * 為這個驅動制定一個默認的統一的行為，提供恢復默認kobj的方法
731 * 沒有釋放kobj內存空間
732 */
733 cdev->kobj.ktype = &ktype_cdev_default;
734 /* [cgw]: 初始化kobject，每個對象都有一個kobject */
735 kobject_init(&cdev->kobj);
736 /* [cgw]: cdev->ops指向驅動程序中的file_operations結構體 */
737 cdev->ops = fops;
738 }
739
740
741
742
743 static struct kobject *base_probe(dev_t dev, int *part, void *data)
744 {
745 if (request_module("char-major-%d-%d", MAJOR(dev), MINOR(dev)) > 0)
746 /* Make old-style 2.4 aliases work */
747 request_module("char-major-%d", MAJOR(dev));
748 return NULL;
749 }
750
751 void __init chrdev_init(void)
752 {
753 /*[cgw]: 初始化cdev_map變量 */
754 cdev_map = kobj_map_init(base_probe, &chrdevs_lock);
755 }
756
757 /* Let modules do char dev stuff */
758 EXPORT_SYMBOL(register_chrdev_region);
759 EXPORT_SYMBOL(unregister_chrdev_region);
760 EXPORT_SYMBOL(alloc_chrdev_region);
761 EXPORT_SYMBOL(cdev_init);
762 EXPORT_SYMBOL(cdev_alloc);
763 EXPORT_SYMBOL(cdev_del);
764 EXPORT_SYMBOL(cdev_add);
765 EXPORT_SYMBOL(register_chrdev);
766 EXPORT_SYMBOL(unregister_chrdev);
767 EXPORT_SYMBOL(directly_mappable_cdev_bdi);
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