{"id":3421,"date":"2011-10-23T12:50:03","date_gmt":"2011-10-23T04:50:03","guid":{"rendered":"http:\/\/edsionte.com\/techblog\/?p=3421"},"modified":"2011-10-23T18:27:35","modified_gmt":"2011-10-23T10:27:35","slug":"%e5%ad%98%e5%82%a8%e6%98%a0%e5%b0%84io","status":"publish","type":"post","link":"http:\/\/edsionte.com\/techblog\/archives\/3421","title":{"rendered":"\u5b58\u50a8\u6620\u5c04I\/O"},"content":{"rendered":"

\u4e00\u4e2a\u8fdb\u7a0b\u62e5\u6709\u72ec\u7acb\u5e76\u4e14\u8fde\u7eed\u865a\u62df\u5730\u5740\u7a7a\u95f4\uff0c\u572832\u4f4d\u4f53\u7cfb\u7ed3\u6784\u4e2d\u8fdb\u7a0b\u7684\u5730\u5740\u7a7a\u95f4\u662f4G\u3002\u4e0d\u8fc7\uff0c\u5185\u6838\u5728\u7ba1\u7406\u8fdb\u7a0b\u7684\u5730\u5740\u7a7a\u95f4\u65f6\u662f\u4ee5\u5185\u5b58\u533a\u57df\u4e3a\u5355\u4f4d\u3002\u5185\u5b58\u533a\u57df\u662f\u8fdb\u7a0b\u6574\u4e2a\u5730\u5740\u7a7a\u95f4\u4e2d\u4e00\u4e2a\u72ec\u7acb\u7684\u5185\u5b58\u8303\u56f4\uff0c\u5b83\u5728\u5185\u6838\u4e2d\u4f7f\u7528vm_area_struct\u6570\u636e\u7ed3\u6784\u6765\u63cf\u8ff0\u3002\u6bcf\u4e2a\u5185\u5b58\u533a\u57df\u90fd\u6709\u81ea\u5df1\u8bbf\u95ee\u6743\u9650\u4ee5\u53ca\u64cd\u4f5c\u51fd\u6570\uff0c\u56e0\u6b64\u8fdb\u7a0b\u53ea\u80fd\u5bf9\u6709\u6548\u8303\u56f4\u7684\u5185\u5b58\u5730\u5740\u8fdb\u884c\u8bbf\u95ee\u3002<\/p>\n

\u5b58\u50a8\u6620\u5c04I\/O\u662f\u4e00\u79cd\u57fa\u4e8e\u5185\u5b58\u533a\u57df\u7684\u9ad8\u7ea7I\/O\u64cd\u4f5c\uff0c\u5b83\u5c06\u78c1\u76d8\u6587\u4ef6\u4e0e\u8fdb\u7a0b\u5730\u5740\u7a7a\u95f4\u4e2d\u7684\u4e00\u4e2a\u5185\u5b58\u533a\u57df\u76f8\u6620\u5c04\u3002\u5f53\u4ece\u8fd9\u6bb5\u5185\u5b58\u4e2d\u8bfb\u6570\u636e\u65f6\uff0c\u5c31\u76f8\u5f53\u4e8e\u8bfb\u78c1\u76d8\u6587\u4ef6\u4e2d\u7684\u6570\u636e\uff0c\u5c06\u6570\u636e\u5199\u5165\u8fd9\u6bb5\u5185\u5b58\u65f6\uff0c\u5219\u76f8\u5f53\u4e8e\u5c06\u6570\u636e\u76f4\u63a5\u5199\u5165\u78c1\u76d8\u6587\u4ef6\u3002\u8fd9\u6837\u5c31\u53ef\u4ee5\u5728\u4e0d\u4f7f\u7528\u57fa\u672cI\/O\u64cd\u4f5c\u51fd\u6570read\u548cwrite\u7684\u60c5\u51b5\u4e0b\u6267\u884cI\/O\u64cd\u4f5c\u3002<\/p>\n

1.\u57fa\u672c\u5b9e\u73b0\u65b9\u6cd5<\/h3>\n

\u5b9e\u73b0\u5b58\u50a8\u6620\u5c04I\/O\u7684\u6838\u5fc3\u64cd\u4f5c\u662f\u901a\u8fc7mmap\u7cfb\u7edf\u8c03\u7528\u5c06\u4e00\u4e2a\u7ed9\u5b9a\u7684\u78c1\u76d8\u6587\u4ef6\u6620\u5c04\u5230\u4e00\u4e2a\u5b58\u50a8\u533a\u57df\u4e2d\u3002<\/p>\n

void *mmap(void *addr, size_t length, int prot, int flags, int fd, off_t offset);<\/pre>\n
\u5173\u4e8e\u8be5\u51fd\u6570\u5b9a\u4e49\u4e2d\u5404\u4e2a\u53c2\u6570\u8bf4\u660eLinux\u4e0a\u7684man\u624b\u518c\u5df2\u7ecf\u89e3\u91ca\u7684\u5f88\u6e05\u695a\uff0c\u5728\u6b64\u4e0d\u518d\u8d58\u8ff0\u3002\u8fd9\u91cc\u9700\u8981\u7279\u522b\u8bf4\u660e\u7684\u662fprot\u548cflags\u53c2\u6570\u3002prot\u7528\u6765\u6307\u5b9a\u5bf9\u6620\u5c04\u533a\u57df\u7684\u4fdd\u62a4\u8981\u6c42\uff0c\u4f46\u662f\u5b83\u7684\u4fdd\u62a4\u8303\u56f4\u4e0d\u80fd\u8d85\u8fc7\u6587\u4ef6open\u65f6\u6307\u5b9a\u7684\u6253\u5f00\u6743\u9650\u3002\u6bd4\u5982\u4ee5\u53ea\u8bfb(PROT_READ)\u65b9\u5f0f\u6253\u5f00\u4e00\u4e2a\u6587\u4ef6\uff0c\u90a3\u4e48\u4ee5\u8bfb\u5199(PROT_READ|PROT_WRITE)\u65b9\u5f0f\u4fdd\u62a4\u5185\u5b58\u533a\u57df\u662f\u4e0d\u5408\u6cd5\u7684\u3002flags\u7528\u6765\u6307\u5b9a\u5185\u5b58\u533a\u57df\u7684\u591a\u79cd\u5c5e\u6027\uff0c\u4e24\u4e2a\u5178\u578b\u7684\u53d6\u503c\u662fMAP_SHARED\u548cMAP_PRIVATE\u3002MAP_SHARED\u6807\u5fd7\u6307\u5b9a\u4e86\u8fdb\u7a0b\u5bf9\u5185\u5b58\u533a\u57df\u7684\u4fee\u6539\u4f1a\u5f71\u54cd\u5230\u6620\u5c04\u6587\u4ef6\u3002\u800c\u5f53\u5bf9flags\u6307\u5b9aMAP_PRIVATE\u65f6\uff0c\u8fdb\u7a0b\u4f1a\u4e3a\u8be5\u6620\u5c04\u5185\u5b58\u533a\u57df\u521b\u5efa\u4e00\u4e2a\u79c1\u6709\u526f\u672c\uff0c\u5bf9\u8be5\u5185\u5b58\u533a\u7684\u6240\u6709\u64cd\u4f5c\u90fd\u662f\u5728\u8fd9\u4e2a\u526f\u672c\u4e0a\u8fdb\u884c\u7684\uff0c\u6b64\u65f6\u5bf9\u5185\u5b58\u533a\u57df\u7684\u4fee\u6539\u5e76\u4e0d\u4f1a\u5f71\u54cd\u5230\u6620\u5c04\u6587\u4ef6\u3002<\/p>\n
\u4e0b\u9762\u5217\u51fa\u4e00\u4e2a\u7b80\u5355\u7684\u793a\u4f8b\u7a0b\u5e8f\uff0c\u5b83\u5c06\u78c1\u76d8\u6587\u4ef6\u6620\u5c04\u5230\u4e00\u4e2a\u5185\u5b58\u533a\u57df\u4e2d\uff0c\u901a\u8fc7mmap\u8fd4\u56de\u7684\u6307\u9488\u5148\u8bfb\u6587\u4ef6\uff0c\u518d\u5199\u6587\u4ef6\u3002\u53ef\u4ee5\u770b\u5230\u5bf9\u6587\u4ef6\u7684\u8bfb\u548c\u5199\u64cd\u4f5c\u90fd\u662f\u901a\u8fc7\u5185\u5b58\u6620\u5c04I\/O\u7684\u65b9\u5f0f\u5b8c\u6210\u7684\u3002<\/p>\n
int main()\r\n{\r\n\tint fd;\r\n\tchar *buf = NULL;\r\n\tint i;\r\n\r\n\t\/\/\u6253\u5f00\u4e00\u4e2a\u6587\u4ef6\r\n\tif (-1 == (fd = open(\".\/mapping_file.txt\", O_RDWR))) {\r\n\t\tprintf(\"open file error!\\n\");\r\n\t\texit(1);\r\n\t}\r\n\r\n\t\/\/\u5c06\u6587\u4ef6\u6620\u5c04\u5230\u8fdb\u7a0b\u7684\u4e00\u4e2a\u5185\u5b58\u533a\u57df\r\n\tbuf = mmap(NULL, 100, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);\r\n\tif (!buf) {\r\n\t\tprintf(\"mmap error!\\n\");\r\n\t\texit(1);\r\n\t}\r\n\r\n\t\/\/\u5bf9\u6620\u5c04\u5185\u5b58\u8bfb\u6570\u636e\r\n\tfor (i = 0; i < 100; i++)\r\n\tprintf(\"%c\", buf[i]);\r\n\r\n\t\/\/\u5bf9\u6620\u5c04\u5185\u5b58\u5199\u6570\u636e\r\n\tif (buf[0] == 'H')\r\n\t\tbuf[0] = 'h';\r\n\telse\r\n\t\tbuf[0] = 'H';\r\n\r\n\tsystem(\"cat .\/mapping_file.txt\");\r\n\treturn 0;\r\n}<\/pre>\n
2.\u4f7f\u7528\u5185\u5b58\u6620\u5c04I\/O\u8fdb\u884c\u6587\u4ef6\u62f7\u8d1d<\/h3>\n
\u4f7f\u7528\u57fa\u672cI\/O\u64cd\u4f5c\u51fd\u6570\u5982\u4f55\u5b9e\u73b0\u4e00\u4e2a\u7c7b\u4f3ccp\u547d\u4ee4\u7684\u7a0b\u5e8f\uff1f\u6bd4\u5982\u6211\u4eec\u8981\u5c06A\u6587\u4ef6\u590d\u5236\u5230B\u6587\u4ef6\uff0c\u90a3\u4e48\u7a0b\u5e8f\u7684\u57fa\u672c\u6846\u67b6\u662f\u8fd9\u6837\u7684\uff1a<\/p>\n
1.open()\u6587\u4ef6A\u548c\u6587\u4ef6B<\/strong><\/p>\n
2.\u5c06A\u6587\u4ef6\u7684\u5185\u5bb9read()\u5230buffer<\/strong><\/p>\n
3.\u5c06buffer\u4e2d\u7684\u6570\u636ewrite()\u5230\u6587\u4ef6B<\/strong><\/p>\n
4.close()\u6587\u4ef6A\u548c\u6587\u4ef6B<\/strong><\/p>\n
\u5982\u679c\u4f7f\u7528\u5185\u5b58\u6620\u5c04I\/O\u6765\u5b9e\u73b0cp\u547d\u4ee4\uff0c\u90a3\u4e48\u5b83\u7684\u57fa\u672c\u6846\u67b6\u662f\u8fd9\u6837\u7684\uff1a<\/p>\n
1.open()\u6587\u4ef6A\u548c\u6587\u4ef6B<\/strong><\/p>\n
2.mmap()\u6587\u4ef6A\u548c\u6587\u4ef6B\uff0c\u5176\u4e2dsrc\u548cdest\u5206\u522b\u4e3a\u4e24\u4e2a\u6587\u4ef6\u6620\u5c04\u5230\u5185\u5b58\u7684\u5730\u5740<\/strong><\/p>\n
3.\u5c06\u4ee5src\u4e3a\u8d77\u59cb\u7684len\u957f\u5b57\u8282\u6570\u636ememcpy()\u5230dest<\/strong><\/p>\n
4.close()\u6587\u4ef6A\u548c\u6587\u4ef6B<\/strong><\/p>\n
\u793a\u4f8b\u7a0b\u5e8f\u5982\u4e0b\uff1a<\/p>\n
int main()\r\n{\r\n\tint srcfd, destfd;\r\n\tstruct stat statbuf;\r\n\tchar *src = NULL, *dest = NULL;\r\n\r\n\t\/\/\u6253\u5f00\u4e24\u4e2a\u6587\u4ef6\r\n\tif (-1 == (srcfd = open(\".\/src.txt\", O_RDONLY))) {\r\n\t\tprintf(\"open src file error!\\n\");\r\n\t\texit(1);\r\n\t}\r\n\r\n\tif (-1 == (destfd = open(\".\/dest.txt\", O_RDWR | O_CREAT | O_TRUNC))) {\r\n\t\tprintf(\"open dest file error!\\n\");\r\n\t\texit(1);\r\n\t}\r\n\r\n\t\/\/\u83b7\u53d6\u539f\u59cb\u6587\u4ef6\u7684\u957f\u5ea6\r\n\tif (-1 == fstat(srcfd, &statbuf)) {\r\n\t\tprintf(\"fstat src file error!\\n\");\r\n\t\texit(1);\r\n\t}\r\n\r\n\t\/\/\u8bbe\u7f6e\u8f93\u51fa\u6587\u4ef6\u7684\u5927\u5c0f\r\n\tif (-1 == lseek(destfd, statbuf.st_size - 1, SEEK_SET)) {\r\n\t\tprintf(\"lseek error!\\n\");\r\n\t\texit(1);\r\n\t}\r\n\tif (-1 == write(destfd, \"\", 1)) {\r\n\t\tprintf(\"write error!\\n\");\r\n\t\texit(1);\r\n\t}\r\n\r\n\tif ((src = mmap(0, statbuf.st_size, PROT_READ, MAP_SHARED, srcfd, 0)) == MAP_FAILED) {\r\n\t\tprintf(\"mmaping src file error!\\n\");\r\n\t\texit(1);\r\n\t}\r\n\r\n\tif ((dest = mmap(0, statbuf.st_size + 2, PROT_READ | PROT_WRITE, MAP_SHARED, destfd, 0)) == MAP_FAILED) {\r\n\t\tprintf(\"mmaping dest file error!\\n\");\r\n\t\texit(1);\r\n\t}\r\n\r\n\tmemcpy(dest, src, statbuf.st_size);\r\n\r\n\tprintf(\"src file:\\n\");\r\n\tsystem(\"cat .\/src.txt\");\r\n\tprintf(\"dest file:\\n\");\r\n\tsystem(\"cat .\/dest.txt\");\r\n\r\n\tclose(srcfd);\r\n\tclose(destfd);\r\n\r\n\treturn 0;\r\n}<\/pre>\n
\u6309\u7167\u4e0a\u8ff0\u5217\u51fa\u7684\u57fa\u672c\u6846\u67b6\uff0c\u8be5\u7a0b\u5e8f\u9996\u5148\u6253\u5f00\u4e24\u4e2a\u6587\u4ef6\uff0c\u901a\u8fc7fstat()\u83b7\u5f97\u6e90\u6587\u4ef6\u7684\u957f\u5ea6\u3002\u56e0\u4e3a\u5728mmap\u4e24\u4e2a\u6587\u4ef6\u4ee5\u53ca\u8bbe\u7f6e\u76ee\u7684\u6587\u4ef6\u957f\u5ea6\u65f6\u90fd\u9700\u8981\u6e90\u6587\u4ef6\u7684\u957f\u5ea6\u3002\u8bbe\u7f6e\u76ee\u7684\u6587\u4ef6\u901a\u8fc7lseek()\u5373\u53ef\u5b8c\u6210\uff0c\u5982\u679c\u6ca1\u6709\u8bbe\u7f6e\u76ee\u7684\u6587\u4ef6\u7684\u957f\u5ea6\uff0c\u90a3\u4e48\u5c06\u4f1a\u4ea7\u751f\u603b\u7ebf\u9519\u8bef\uff08\u5f15\u53d1\u4fe1\u53f7SIGBUS\uff09\u3002\u7136\u540e\u5206\u522bmmap()\u4e24\u4e2a\u6587\u4ef6\u5230\u8fdb\u7a0b\u7684\u5730\u5740\u7a7a\u95f4\uff0c\u6700\u540e\u8c03\u7528memcpy()\u5c06\u6e90\u6587\u4ef6\u5185\u5b58\u533a\u7684\u6570\u636e\u62f7\u8d1d\u5230\u76ee\u7684\u6587\u4ef6\u5185\u5b58\u533a\u3002<\/p>\n
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