18-vmem_disk IO请求处理
13.7.4 vmem_disk I/O请求处理
在vmem_disk驱动中，通过模块参数request_mode的方式来支持3种不同的请求处理模式以加深读者对它们的理解，代码清单13.19列出了vmem_disk驱动的请求处理代码。
代码清单13.19 vmem.disk设备驱动的请求处理函数
1 /*
2 * 处理一个I/O request.
3 */
4 static void vmem_disk_transfer(struct vmem_disk_dev *dev, unsigned long sector,
5 unsigned long nsect, char *buffer, int write)
6 {
7 unsigned long offset = sector*KERNEL_SECTOR_SIZE;
8 unsigned long nbytes = nsect*KERNEL_SECTOR_SIZE;
9
10 if ((offset + nbytes) > dev->size) {
11 printk (KERN_NOTICE "Beyond-end write (%ld %ld)\n", offset, nbytes);
12 return;
13 }
14 if (write)
15 memcpy(dev->data + offset, buffer, nbytes);
16 else
17 memcpy(buffer, dev->data + offset, nbytes);
18 }
19
20 /*
21 * request函数的简单形式
22 */
23 static void vmem_disk_request(struct request_queue *q)
24 {
25 struct request *req;
26
27 while ((req = elv_next_request(q)) != NULL) {
28 struct vmem_disk_dev *dev = req->rq_disk->private_data;
29 if (! blk_fs_request(req)) {
30 printk (KERN_NOTICE "Skip non-fs request\n");
31 end_request(req, 0);
32 continue;
33 }
34
35 vmem_disk_transfer(dev, req->sector, req->current_nr_sectors,
36 req->buffer, rq_data_dir(req));
37
38 end_request(req, 1);
39 }
40 }
41
42
43 /*
44 * 传输一个单独的BIO
45 */
46 static int vmem_disk_xfer_bio(struct vmem_disk_dev dev, struct bio bio)
47 {
48 int i;
49 struct bio_vec *bvec;
50 sector_t sector = bio->bi_sector;
51
52 / Do each segment independently. /
53 bio_for_each_segment(bvec, bio, i) {
54 char *buffer = __bio_kmap_atomic(bio, i, KM_USER0);
55 vmem_disk_transfer(dev, sector, bio_cur_sectors(bio),
56 buffer, bio_data_dir(bio) == WRITE);
57 sector += bio_cur_sectors(bio);
58 __bio_kunmap_atomic(bio, KM_USER0);
59 }
60 return 0; / Always "succeed" /
61 }
62
63 /*
64 * 传输一个完整的request
65 */
66 static int vmem_disk_xfer_request(struct vmem_disk_dev dev, struct request req)
67 {
68
69 struct req_iterator iter;
70 int nsect = 0;
71 struct bio_vec *bvec;
72
73 rq_for_each_segment(bvec, req, iter) {
74 char *buffer = __bio_kmap_atomic(iter.bio, iter.i, KM_USER0);
75 sector_t sector = iter.bio->bi_sector;
76 vmem_disk_transfer(dev, sector, bio_cur_sectors(iter.bio),
77 buffer, bio_data_dir(iter.bio) == WRITE);
78 sector += bio_cur_sectors(iter.bio);
79 __bio_kunmap_atomic(iter.bio, KM_USER0);
80 nsect += iter.bio->bi_size/KERNEL_SECTOR_SIZE;
81 }
82 return nsect;
83 }
84
85
86 /*
87 * 更强大的request处理
88 */
89 static void vmem_disk_full_request(struct request_queue *q)
90 {
91 struct request *req;
92 int sectors_xferred;
93 struct vmem_disk_dev *dev = q->queuedata;
94
95 while ((req = elv_next_request(q)) != NULL) {
96 if (! blk_fs_request(req)) {
97 printk (KERN_NOTICE "Skip non-fs request\n");
98 end_request(req, 0);
99 continue;
100 }
101 sectors_xferred = vmem_disk_xfer_request(dev, req);
102 end_request (req, 1);
103 }
104 }
105
106 /*
107 * "制造请求"方式
108 */
109 static int vmem_disk_make_request(struct request_queue q, struct bio bio)
110 {
111 struct vmem_disk_dev *dev = q->queuedata;
112 int status;
113
114 status = vmem_disk_xfer_bio(dev, bio);
115 bio_endio(bio, status);
116 return 0;
117 }
上述代码中的1～40行、43～104行、106～117行分别对应了RM_SIMPLE、RM_FULL、RM_NOQUEUE这3种不同的请求处理方式。
vmem_disk的驱动位于VirtualBox虚拟机映像的/home/lihacker/develop/svn/ldd6410-read-only/ training/kernel/drivers/ vmem_disk下面，已经有编写好的Makefile，直接在其中运行make命令即可得到vmem_disk.ko模块。