05-MTD用户空间编程
19.1.3 MTD用户空间编程
drivers/mtd/mtdchar.c文件实现了MTD字符设备接口，通过它，用户可以直接操作Flash设备。通过read()、write()系统调用可以读写Flash，通过一系列IOCTL命令可以获取Flash设备信息、擦除Flash、读写NAND的OOB、获取OOB layout及检查NAND坏块等。
代码清单19.5所示为MEMGETINFO、MEMERASE、MEMREADOOB、MEMWRITEOOB、MEMGETBADBLOCK IOCRL的例子。
代码清单19.5 /dev/mtdX IOCTL演示范例
1 mtd_oob_buf oob;
2 erase_info_user erase;
3 mtd_info_user meminfo;
4
5 /得到MTD设备信息/
6 if (ioctl(fd, MEMGETINFO, &meminfo) != 0)
7 perror("ioctl(MEMGETINFO)");
8
9 /擦除块/
10 if (ioctl(ofd, MEMERASE, &erase) != 0) {
11 perror("ioctl(MEMERASE)");
12 goto error;
13 }
14
15 /读OOB /
16 if (ioctl(fd, MEMREADOOB, &oob) != 0)
17 perror("ioctl(MEMREADOOB)");
18
19 /写OOB /
20 if (ioctl(fd, MEMWRITEOOB, &oob) != 0) {
21 fprintf(stderr, "\n%s: %s: MTD writeoob failure: %s\n", exe_name, mtd_device,
22 strerror(errno));
23 }
24
25 /检查坏块/
26 if (blockstart != (ofs &(~meminfo.erasesize + 1))) {
27 blockstart = ofs &(~meminfo.erasesize + 1);
28 if ((badblock = ioctl(fd, MEMGETBADBLOCK, &blockstart)) < 0)
29 perror("ioctl(MEMGETBADBLOCK)");
30 else if (badblock) {/是坏块/
31 ...
32 } else/是好块/
33 ...
34 }
代码清单19.6所示的过程如下：它读取记录在一个映像文件中的针对NAND的数据信息，并把它写到NAND Flash中。代码中涉及大量IOCTL的调用及NAND的擦除和写入过程（含坏块检查），mtd-utils中nand_write、flash_eraseall等工具也是借助类似方法实现的。
代码清单19.6 /dev/mtdX用户空间编程综合范例
1 int main(int argc, char **argv)
2 {
3 struct mtd_info_user meminfo;
4 struct mtd_oob_buf oob;
5 char oobbuf[MAX_OOB_SIZE];
6 ...
7
8 memset(oobbuf, 0xff, sizeof(oobbuf));
9
10 / 打开/dev/mtdX /
11 if ((fd = open(mtd_device, O_RDWR)) == - 1) {
12 perror("open Flash");
13 exit(1);
14 }
15
16 / 填充MTD设备容量结构体 /
17 if (ioctl(fd, MEMGETINFO, &meminfo) != 0) {
18 perror("MEMGETINFO");
19 close(fd);
20 exit(1);
21 }
22
23 oob.length = meminfo.oobsize;
24 oob.ptr = oobbuf;
25
26 / 打开输入文件 /
27 if ((ifd = open(img, O_RDONLY)) == - 1) {
28 perror("open input file");
29 goto restoreoob;
30 }
31
32
33 imglen = lseek(ifd, 0, SEEK_END); / 得到映像长度 /
34 lseek(ifd, 0, SEEK_SET);
35
36 pagelen = meminfo.oobblock + meminfo.oobsize; /一页的（数据+oob）长度/
37 ...
38
39 / 从输入文件读数据然后写入MTD设备 /
40 while (imglen && (mtdoffset < meminfo.size)) {
41 / 在擦除块之前检查是否为坏块 /
42 while (blockstart != (mtdoffset &(~meminfo.erasesize + 1))) {
43 blockstart = mtdoffset &(~meminfo.erasesize + 1);
44 offs = blockstart;
45 baderaseblock = 0;
46 if (!quiet)
47 fprintf(stdout, "Writing data to block %x\n", blockstart);
48
49 / 检查坏块 /
50 do {
51 if ((ret = ioctl(fd, MEMGETBADBLOCK, &offs)) < 0) {
52 perror("ioctl(MEMGETBADBLOCK)");
53 goto closeall;
54 }
55 if (ret == 1) {
56 baderaseblock = 1;
57 if (!quiet)
58 fprintf(stderr,
59 "Bad block at %x, %u block(s) from %x will be skipped\n",
60 (int)offs, blockalign, blockstart);
61 }
62 if (baderaseblock) {
63 mtdoffset = blockstart + meminfo.erasesize;
64 }
65 offs += meminfo.erasesize / blockalign;
66 } while (offs < blockstart + meminfo.erasesize);
67 }
68
69 readlen = meminfo.oobblock;
70
71 / 从输入文件中读page数据 /
72 if ((cnt = read(ifd, writebuf, readlen)) != readlen) {
73 if (cnt == 0) / EOF /
74 break;
75 perror("File I/O error on input file");
76 goto closeall;
77 }
78
79 / 从输入文件读OOB数据 /
80 if ((cnt = read(ifd, oobreadbuf, meminfo.oobsize)) != meminfo.oobsize) {
81 perror("File I/O error on input file");
82 goto closeall;
83 }
84
85 / 将OOB数据写入设备 /
86 oob.start = mtdoffset;
87 if (ioctl(fd, MEMWRITEOOB, &oob) != 0) {
88 perror("ioctl(MEMWRITEOOB)");
89 goto closeall;
90 }
91
92 / 写page数据 /
93 if (pwrite(fd, writebuf, meminfo.oobblock, mtdoffset) != meminfo.oobblock) {
94 perror("pwrite");
95 goto closeall;
96 }
97 imglen -= readlen;
98 mtdoffset += meminfo.oobblock;
99 }
100
101 closeall: ...
102 return 0;
103 }