{"id":4499,"date":"2015-03-03T18:27:53","date_gmt":"2015-03-03T10:27:53","guid":{"rendered":"http:\/\/edsionte.com\/techblog\/?p=4499"},"modified":"2015-12-16T10:23:28","modified_gmt":"2015-12-16T02:23:28","slug":"open%e5%9c%a8linux%e5%86%85%e6%a0%b8%e7%9a%84%e5%ae%9e%e7%8e%b05-%e6%99%ae%e9%80%9a%e7%9b%ae%e5%bd%95%e9%a1%b9%e7%9a%84%e5%a4%84%e7%90%86","status":"publish","type":"post","link":"http:\/\/edsionte.com\/techblog\/archives\/4499","title":{"rendered":"open()\u5728Linux\u5185\u6838\u7684\u5b9e\u73b0(4)-\u666e\u901a\u76ee\u5f55\u9879\u7684\u5904\u7406"},"content":{"rendered":"<h2>1.\u57fa\u672c\u8bf4\u660e<\/h2>\n<p>\u5728open()\u7684\u8def\u5f84\u67e5\u627e\u8fc7\u7a0b\u4e2d\uff0cwalk_component()\u5c06\u5bf9\u8def\u5f84\u4e2d\u7684\u6bcf\u4e2a\u76ee\u5f55\u9879\u8fdb\u884c\u904d\u5386\uff0c\u5f53\u76ee\u5f55\u9879\u4e3a\u666e\u901a\u76ee\u5f55\u9879\u65f6\uff0c\u5c06\u901a\u8fc7do_lookup()\u5bf9\u5176\u8fdb\u884c\u67e5\u627e\u3002\u5728\u8def\u5f84\u67e5\u627e\u8fc7\u7a0b\u4e2d\uff0c\u666e\u901a\u76ee\u5f55\u9879\u7b97\u662f\u6bd4\u8f83\u5e38\u89c1\u7684\uff0c\u56e0\u6b64\u66f4\u5e94\u8be5\u91c7\u53d6\u9ad8\u6548\u7684\u65b9\u6cd5\u8282\u7701\u67e5\u627e\u65f6\u95f4\u3002<\/p>\n<p>\u4e3a\u4e86\u63d0\u9ad8\u67e5\u627e\u6548\u7387\uff0c\u5185\u6838\u901a\u8fc7rcu-walk\u65b9\u5f0f\u907f\u514dref-walk\u7531\u4e8e\u9501\u673a\u5236\u800c\u5f15\u5165\u7684\u963b\u585e\u95ee\u9898\uff1b\u5176\u6b21\uff0c\u5185\u6838\u901a\u8fc7dentry\u7f13\u5b58\u7684\u65b9\u5f0f\u5c06\u76ee\u5f55\u9879\u4ee5\u54c8\u5e0c\u8868\u7684\u65b9\u5f0f\u7ec4\u7ec7\u8d77\u6765\uff0c\u4ee5\u4fbf\u63d0\u9ad8\u67e5\u627e\u6548\u7387\u3002\u8fd9\u4e24\u79cd\u65b9\u5f0f\u5728\u4e00\u5b9a\u7a0b\u5ea6\u4e0a\u53ef\u4ee5\u63d0\u9ad8\u8def\u5f84\u67e5\u627e\u7684\u6548\u7387\uff0c\u4e0d\u8fc7\u5b83\u4eec\u5e76\u4e0d\u662f\u9002\u5408\u6240\u6709\u60c5\u51b5\u3002\u6bd4\u5982\uff0crcu-walk\u65b9\u5f0f\u4e0d\u80fd\u4f7f\u7528\u53ef\u80fd\u4f1a\u5f15\u8d77\u963b\u585e\u7684\u51fd\u6570\uff0c\u6709\u65f6\u5019\u8981\u67e5\u627e\u7684\u76ee\u5f55\u9879\u5e76\u4e0d\u4f4d\u4e8e\u7f13\u5b58\u5f53\u4e2d\u800c\u53ea\u80fd\u4ece\u78c1\u76d8\u4e0a\u83b7\u53d6\u4fe1\u606f\u3002<\/p>\n<p>\u7531\u4e8e\u4e0a\u8ff0\u63d0\u9ad8\u67e5\u627e\u6548\u7387\u7684\u65b9\u5f0f\u53ef\u80fd\u4f1a\u67e5\u627e\u5931\u8d25\uff0c\u56e0\u6b64\u5185\u6838\u4e00\u822c\u4f1a\u7ecf\u8fc7\u591a\u6b21\u76ee\u5f55\u9879\u7684\u67e5\u627e\u3002\u4e5f\u5c31\u662f\u8bf4\uff0c\u5185\u6838\u4f1a\u5148\u8fdb\u884c\u9ad8\u6548\u7684\u67e5\u627e\u65b9\u5f0f\uff0c\u5982\u679c\u5728\u8fd9\u79cd\u6a21\u5f0f\u4e0b\u67e5\u627e\u5931\u8d25\uff0c\u90a3\u4e48\u518d\u8fdb\u884c\u4f20\u7edf\u7684\u67e5\u627e\u65b9\u5f0f\uff0c\u4fdd\u8bc1\u67e5\u627e\u5de5\u4f5c\u7684\u6b63\u5e38\u8fdb\u884c\u3002\u5177\u4f53\u7684\uff0c\u5185\u6838\u4f1a\u5148\u8fdb\u884crcu-walk\u65b9\u5f0f\uff0c\u5982\u679c\u67e5\u627e\u5931\u8d25\uff0c\u5219\u8fdb\u884cref-walk\u65b9\u5f0f\uff1b\u5185\u6838\u4f1a\u4f18\u5148\u5728\u76ee\u5f55\u9879\u7f13\u5b58\u4e2d\u8fdb\u884c\u5feb\u901f\u7684\u67e5\u627e\uff0c\u5982\u679c\u67e5\u627e\u5931\u8d25\uff0c\u5219\u901a\u8fc7\u8bbf\u95ee\u78c1\u76d8\u8fdb\u884c\u6162\u901f\u7684\u67e5\u627e\u3002<\/p>\n<h2>2.\u51fd\u6570\u5b9e\u73b0<\/h2>\n<h3>2.1.do_lookup()<\/h3>\n<p>\u5185\u6838\u901a\u8fc7do_lookup()\u8fdb\u884c\u666e\u901a\u76ee\u5f55\u9879\u7684\u67e5\u627e\u5de5\u4f5c\u3002\u8be5\u51fd\u6570\u58f0\u660e\u5982\u4e0b\uff1a<\/p>\n<pre class=\"brush: cpp; title: ; notranslate\" title=\"\">\r\ntatic int do_lookup(struct nameidata *nd, struct qstr *name,\r\n\tstruct path *path, struct inode **inode);\r\n<\/pre>\n<p>\u8fd9\u4e2a\u51fd\u6570\u4e3b\u8981\u901a\u8fc7\u533a\u5206\u4e0d\u540c\u7684\u60c5\u666f\u6765\u9009\u62e9\u5bf9\u5e94\u7684\u67e5\u627e\u65b9\u5f0f\u3002\u603b\u4f53\u6765\u8bf4\uff0c\u5148\u4ee5rcu-walk\u65b9\u5f0f\u5728\u76ee\u5f55\u9879\u7f13\u5b58\u4e2d\u67e5\u627e\uff0c\u5982\u679c\u6210\u529f\uff0c\u5219\u67e5\u627e\u7ed3\u675f\u8fd4\u56de\uff1b\u5426\u5219\uff0c\u5c06rcu-walk\u5207\u6362\u5230ref-walk\u6a21\u5f0f\uff1bref-walk\u6a21\u5f0f\u4e0b\u4f1a\u5148\u8fdb\u884c\u76ee\u5f55\u9879\u7f13\u5b58\u7684\u67e5\u627e\uff0c\u5982\u679c\u67e5\u627e\u6210\u529f\uff0c\u5219\u8fd4\u56de\uff1b\u5426\u5219\uff0c\u8fdb\u884cref-walk\u4e0b\u7684\u78c1\u76d8\u67e5\u627e\uff1b\u5982\u679c\u6210\u529f\uff0c\u5219\u8fd4\u56de\uff0c\u5426\u5219\uff0c\u67e5\u627e\u5931\u8d25\u5e76\u8fd4\u56de\u9519\u8bef\u7801ENOENT\uff1b\u8be5\u9519\u8bef\u7801\u5bf9\u5e94\u5230\u7528\u6237\u6001\u5373\u4e3a\u201cNo such file or directory\u201d\u3002<\/p>\n<p>\u5982\u679c\u4ee5rcu-walk\u6a21\u5f0f\u8fdb\u5165\u8be5\u51fd\u6570\uff0c\u5219\u4e3b\u8981\u7684\u67e5\u627e\u6b65\u9aa4\u5982\u4e0b\uff1a<\/p>\n<p>1.\u5982\u679c\u5f53\u524d\u662frcu-walk\u6a21\u5f0f\uff08\u8bbe\u7f6e\u4e86LOOKUP_RCU\uff09\uff0c\u5219\u5148\u901a\u8fc7__d_lookup_rcu\u5728\u76ee\u5f55\u9879\u7f13\u5b58\u4e2d\u67e5\u627e\uff1b<\/p>\n<p>2.\u5982\u679c\u67e5\u627e\u5931\u8d25\uff0c\u5219\u8df3\u5165unlazy\u6807\u53f7\u5904\uff1b\u5982\u679c\u67e5\u627e\u6210\u529f\uff0c\u5219\u7ee7\u7eed\uff1b<\/p>\n<p>3.\u901a\u8fc7follow_mount_rcu()\u5224\u65ad\u5f53\u524d\u7684\u76ee\u5f55\u9879\u662f\u5426\u4e3a\u6302\u8f7d\u70b9\uff0c\u5982\u679c\u662f\uff0c\u5219\u8de8\u8d8a\u6302\u8f7d\u70b9\uff1b\u5426\u5219\u7ee7\u7eed\uff1b<\/p>\n<p>4.\u5982\u679crcu-walk\u65b9\u5f0f\u4e0b\u67e5\u627e\u7f13\u5b58\u6210\u529f\uff0c\u5219\u8fd4\u56de0\uff1b\u5426\u5219\uff0c\u8fdb\u5165unlazy\u6807\u53f7\uff1b<\/p>\n<p>5.unlazy\u6807\u53f7\u662f\u5c06\u5f53\u524d\u7684rcu-walk\u5207\u6362\u6210ref-walk\u6a21\u5f0f\uff1b\u5982\u679c\u5207\u6362\u6210\u529f\uff0c\u5219\u7ee7\u7eed\uff1b\u5426\u5219\uff0c\u8fd4\u56deECHILD\u3002\u5373\u8fd4\u56de\u5230do_filp_open()\u5904\uff0c\u91cd\u65b0\u8fdb\u884cref\u6a21\u5f0f\u7684\u67e5\u627e\uff1b<\/p>\n<p>6.\u5f53\u524d\u67e5\u627e\u6a21\u5f0f\u4e3aref-walk\uff0c\u5e76\u4e14\u6b64\u65f6\u5728\u7f13\u5b58\u4e2d\u5e76\u672a\u627e\u5230\u5bf9\u5e94\u7684\u76ee\u5f55\u9879\uff1b\u90a3\u4e48\u63a5\u4e0b\u6765\u5fc5\u987b\u8bd5\u56fe\u5728\u78c1\u76d8\u4e0a\u8fdb\u884c\u67e5\u627e\u4e86\u3002\u4e0d\u8fc7\u5728\u8fdb\u884c\u78c1\u76d8\u67e5\u627e\u4e4b\u524d\uff0c\u8fd8\u662f\u4f1a\u518d\u6b21\u8c03\u7528d_lookup()\u8fdb\u884c\u4e00\u6b21\u5185\u5b58\u67e5\u627e\uff0c\u56e0\u4e3aretry\u6807\u53f7\u4e0b\u7684\u4ee3\u7801\u6709\u4e92\u65a5\u9501\uff0c\u5f88\u53ef\u80fd\u8be5\u51fd\u6570\u518d\u6b64\u5904\u4f1a\u963b\u585e\uff0c\u800c\u5728\u963b\u585e\u9636\u6bb5\u5c31\u76ee\u6807\u76ee\u5f55\u9879\u5c31\u6709\u53ef\u80fd\u88ab\u8f7d\u5165\u5185\u5b58\uff0c\u8fd9\u6837\u5c31\u53ef\u4ee5\u7701\u53bb\u5728\u78c1\u76d8\u4e0a\u67e5\u627e\u76ee\u5f55\u9879\u7684\u5de5\u4f5c\uff1b<\/p>\n<p>7.\u5982\u679cd_lookup()\u67e5\u627e\u6210\u529f\uff0c\u5219\u7ee7\u7eed\uff1b\u5426\u5219\uff0c\u901a\u8fc7d_alloc_and_lookup()\u5206\u914d\u5e76\u5728\u78c1\u76d8\u4e0a\u67e5\u627edentry\uff1b\u5177\u4f53\u7684\uff0c\u8c03\u7528\u5f53\u524d\u6587\u4ef6\u7cfb\u7edf\u7684lookup\u94a9\u5b50\u51fd\u6570\uff1b\u5982\u679c\u78c1\u76d8\u67e5\u627e\u5931\u8d25\uff0c\u5219\u9519\u8bef\u8fd4\u56de\uff1b\u5426\u5219\uff0c\u7ee7\u7eed\uff1b<\/p>\n<p>8.\u6b64\u65f6\uff0c\u5df2\u83b7\u53d6\u5230\u8981\u67e5\u627e\u7684\u76ee\u5f55\u9879\uff1b\u5219\u518d\u901a\u8fc7follow_managed()\u5bf9\u5f53\u524d\u76ee\u5f55\u9879\u8fdb\u884c\u68c0\u67e5\uff0c\u6bd4\u5982\uff0c\u68c0\u67e5\u5f53\u524d\u76ee\u5f55\u9879\u662f\u5426\u4e3a\u6302\u8f7d\u70b9\uff1b<\/p>\n<p>9.\u83b7\u53d6\u5f53\u524d\u76ee\u5f55\u9879\u5bf9\u5e94\u7684inode\u4fe1\u606f\uff1b<\/p>\n<p>10.\u8fd4\u56de\uff1b<\/p>\n<p>\u5982\u679c\u4ee5ref-walk\u6a21\u5f0f\u8fdb\u5165\u8be5\u51fd\u6570\uff0c\u5219\u9996\u5148\u4f1a\u901a\u8fc7__d_lookup()\u5728\u76ee\u5f55\u9879\u7f13\u5b58\u4e2d\u67e5\u627e\uff1b\u5982\u679c\u67e5\u627e\u6210\u529f\uff0c\u5219\u63a5\u4e0b\u6765\u7684\u6b65\u9aa4\u4e0ercu-walk\u6b65\u9aa48-10\u76f8\u540c\uff1b\u5982\u679c\u67e5\u627e\u5931\u8d25\uff0c\u5219\u63a5\u4e0b\u6765\u7684\u6b65\u9aa4\u4e0ercu-walk\u6b65\u9aa46-10\u76f8\u540c\u3002<\/p>\n<h2>3.\u603b\u7ed3<\/h2>\n<p>\u666e\u901a\u76ee\u5f55\u9879\u7684\u67e5\u627e\u5de5\u4f5c\u5176\u5b9e\u5e76\u4e0d\u590d\u6742\uff0c\u65e0\u975e\u662f\u5728\u5185\u5b58\u4e2d\u67e5\u627e\u6216\u5728\u78c1\u76d8\u4e2d\u67e5\u627e\u3002\u53ea\u4e0d\u8fc7\uff0c\u5185\u6838\u4e3a\u4e86\u63d0\u9ad8\u8def\u5f84\u67e5\u627e\u6548\u7387\u540c\u65f6\u5f15\u5165\u4e86rcu-walk\u65b9\u5f0f\uff0c\u4ece\u800c\u589e\u52a0\u4e86\u4ee3\u7801\u5206\u6790\u7684\u590d\u6742\u5ea6\u3002\u5982\u679c\u5f53\u524d\u76ee\u5f55\u9879\u4e3a\u7b26\u53f7\u94fe\u63a5\u6587\u4ef6\uff0c\u5219\u5185\u6838\u7684\u5904\u7406\u65b9\u5f0f\u53c8\u662f\u53e6\u4e00\u79cd\u65b9\u5f0f\uff0c\u5177\u4f53\u7684\u5b9e\u73b0\u8fc7\u7a0b\u53ef\u53c2\u89c1\u672c\u7cfb\u5217\u7684\u4e0b\u4e00\u7bc7\u6587\u7ae0\u3002<\/p>\n<p><strong>\u53c2\u8003\u8d44\u6599\uff1a<\/strong><\/p>\n<p><strong>1.Linux\u6e90\u78013.2.69\uff1b<\/strong><\/p>\n<p><strong>2.Linux\u7cfb\u7edf\u8c03\u7528open\u4e03\u65e5\u6e38\uff1ahttp:\/\/blog.chinaunix.net\/uid-20522771-id-4419666.html<\/strong><\/p>\n<p><strong>3.\u6df1\u5165\u7406\u89e3Linux\u5185\u6838\uff1ahttp:\/\/book.douban.com\/subject\/2287506\/\uff1b<\/strong><\/p>\n<p><strong>4.\u6df1\u5165Linux\u5185\u6838\u67b6\u6784\uff1ahttp:\/\/book.douban.com\/subject\/4843567\/\uff1b<\/strong><\/p>\n<p><strong>5.Linux\u5185\u6838\u63a2\u79d8\uff1ahttp:\/\/book.douban.com\/subject\/25817503\/\uff1b<\/strong><\/p>\n","protected":false},"excerpt":{"rendered":"<p>1.\u57fa\u672c\u8bf4\u660e \u5728open()\u7684\u8def\u5f84\u67e5\u627e\u8fc7\u7a0b\u4e2d\uff0cwalk_component()\u5c06\u5bf9\u8def\u5f84\u4e2d\u7684\u6bcf\u4e2a\u76ee\u5f55\u9879\u8fdb\u884c\u904d\u5386\uff0c [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[110,175],"tags":[397,404,393],"class_list":["post-4499","post","type-post","status-publish","format-standard","hentry","category-linux","category-175","tag-do_lookup","tag-404","tag-393"],"views":10397,"_links":{"self":[{"href":"http:\/\/edsionte.com\/techblog\/wp-json\/wp\/v2\/posts\/4499","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/edsionte.com\/techblog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/edsionte.com\/techblog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/edsionte.com\/techblog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/edsionte.com\/techblog\/wp-json\/wp\/v2\/comments?post=4499"}],"version-history":[{"count":7,"href":"http:\/\/edsionte.com\/techblog\/wp-json\/wp\/v2\/posts\/4499\/revisions"}],"predecessor-version":[{"id":4549,"href":"http:\/\/edsionte.com\/techblog\/wp-json\/wp\/v2\/posts\/4499\/revisions\/4549"}],"wp:attachment":[{"href":"http:\/\/edsionte.com\/techblog\/wp-json\/wp\/v2\/media?parent=4499"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/edsionte.com\/techblog\/wp-json\/wp\/v2\/categories?post=4499"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/edsionte.com\/techblog\/wp-json\/wp\/v2\/tags?post=4499"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}