{"id":954,"date":"2021-12-19T12:03:17","date_gmt":"2021-12-19T04:03:17","guid":{"rendered":"https:\/\/blog.cauchyschwarz.com\/?p=954"},"modified":"2021-12-19T12:03:22","modified_gmt":"2021-12-19T04:03:22","slug":"apiue%e8%af%bb%e4%b9%a6%e7%ac%94%e8%ae%b0chapter3","status":"publish","type":"post","link":"https:\/\/blog.cauchyschwarz.com\/?p=954","title":{"rendered":"APIUE\u8bfb\u4e66\u7b14\u8bb0chapter3"},"content":{"rendered":"\n<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_84 ez-toc-wrap-right counter-hierarchy ez-toc-counter ez-toc-grey ez-toc-container-direction\">\n<p class=\"ez-toc-title\" style=\"cursor:inherit\">Table of Contents<\/p>\n<label for=\"ez-toc-cssicon-toggle-item-6a28ec90432ea\" class=\"ez-toc-cssicon-toggle-label\"><span class=\"\"><span class=\"eztoc-hide\" style=\"display:none;\">Toggle<\/span><span class=\"ez-toc-icon-toggle-span\"><svg style=\"fill: #999;color:#999\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" class=\"list-377408\" width=\"20px\" height=\"20px\" viewBox=\"0 0 24 24\" fill=\"none\"><path d=\"M6 6H4v2h2V6zm14 0H8v2h12V6zM4 11h2v2H4v-2zm16 0H8v2h12v-2zM4 16h2v2H4v-2zm16 0H8v2h12v-2z\" fill=\"currentColor\"><\/path><\/svg><svg style=\"fill: #999;color:#999\" class=\"arrow-unsorted-368013\" xmlns=\"http:\/\/www.w3.org\/2000\/svg\" width=\"10px\" height=\"10px\" viewBox=\"0 0 24 24\" version=\"1.2\" baseProfile=\"tiny\"><path d=\"M18.2 9.3l-6.2-6.3-6.2 6.3c-.2.2-.3.4-.3.7s.1.5.3.7c.2.2.4.3.7.3h11c.3 0 .5-.1.7-.3.2-.2.3-.5.3-.7s-.1-.5-.3-.7zM5.8 14.7l6.2 6.3 6.2-6.3c.2-.2.3-.5.3-.7s-.1-.5-.3-.7c-.2-.2-.4-.3-.7-.3h-11c-.3 0-.5.1-.7.3-.2.2-.3.5-.3.7s.1.5.3.7z\"\/><\/svg><\/span><\/span><\/label><input type=\"checkbox\"  id=\"ez-toc-cssicon-toggle-item-6a28ec90432ea\" checked aria-label=\"Toggle\" \/><nav><ul class='ez-toc-list ez-toc-list-level-1 ' ><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/blog.cauchyschwarz.com\/?p=954\/#%E6%96%87%E4%BB%B6%E6%8F%8F%E8%BF%B0%E7%AC%A6\" >\u6587\u4ef6\u63cf\u8ff0\u7b26<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/blog.cauchyschwarz.com\/?p=954\/#open%E5%92%8Copenat%E5%87%BD%E6%95%B0\" >open\u548copenat\u51fd\u6570<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/blog.cauchyschwarz.com\/?p=954\/#creat%E5%87%BD%E6%95%B0\" >creat\u51fd\u6570<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-4\" href=\"https:\/\/blog.cauchyschwarz.com\/?p=954\/#close%E5%87%BD%E6%95%B0\" >close\u51fd\u6570<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-5\" href=\"https:\/\/blog.cauchyschwarz.com\/?p=954\/#lseek%E5%87%BD%E6%95%B0\" >lseek\u51fd\u6570<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-6\" href=\"https:\/\/blog.cauchyschwarz.com\/?p=954\/#read%E5%87%BD%E6%95%B0\" >read\u51fd\u6570<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-7\" href=\"https:\/\/blog.cauchyschwarz.com\/?p=954\/#write%E5%87%BD%E6%95%B0\" >write\u51fd\u6570<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-8\" href=\"https:\/\/blog.cauchyschwarz.com\/?p=954\/#File_Sharing\" >File Sharing<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-9\" href=\"https:\/\/blog.cauchyschwarz.com\/?p=954\/#Atomic_Operations\" >Atomic Operations<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-10\" href=\"https:\/\/blog.cauchyschwarz.com\/?p=954\/#dup%E5%92%8Cdup2%E5%87%BD%E6%95%B0\" >dup\u548cdup2\u51fd\u6570<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-11\" href=\"https:\/\/blog.cauchyschwarz.com\/?p=954\/#sync%E3%80%81fsync%E3%80%81fdatasync%E5%87%BD%E6%95%B0\" >sync\u3001fsync\u3001fdatasync\u51fd\u6570<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-12\" href=\"https:\/\/blog.cauchyschwarz.com\/?p=954\/#fcntl%E5%87%BD%E6%95%B0\" >fcntl\u51fd\u6570<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-13\" href=\"https:\/\/blog.cauchyschwarz.com\/?p=954\/#ioctl%E5%87%BD%E6%95%B0%E6%96%87%E4%BB%B6\" >ioctl\u51fd\u6570\u6587\u4ef6<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-14\" href=\"https:\/\/blog.cauchyschwarz.com\/?p=954\/#devfd%E6%96%87%E4%BB%B6\" >\/dev\/fd\u6587\u4ef6<\/a><\/li><li class='ez-toc-page-1 ez-toc-heading-level-1'><a class=\"ez-toc-link ez-toc-heading-15\" href=\"https:\/\/blog.cauchyschwarz.com\/?p=954\/#Exercises\" >Exercises<\/a><\/li><\/ul><\/nav><\/div>\n<h1 class=\"wp-block-heading\" id=\"e69687e4bbb6e68f8fe8bfb0e7aca6-1\"><span class=\"ez-toc-section\" id=\"%E6%96%87%E4%BB%B6%E6%8F%8F%E8%BF%B0%E7%AC%A6\"><\/span>\u6587\u4ef6\u63cf\u8ff0\u7b26<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">\u5185\u6838\u901a\u8fc7\u6587\u4ef6\u63cf\u8ff0\u7b26\u6765\u5f15\u7528\u6253\u5f00\u7684\u6587\u4ef6\u3002<br>\u6bcf\u4e2a\u8fdb\u7a0b\u6700\u591a\u80fd\u540c\u65f6\u6253\u5f00OPEN_MAX\u4e2a\u6587\u4ef6\u63cf\u8ff0\u7b26\u3002<br>\u4e00\u822c\u524d3\u4e2a\u662f\uff1aSTDIN_FILENO(0), STDOUT_FILENO(1), STDERR_FILENO(2)\uff0c\u8fd9\u4e9b\u5e38\u91cf\u5728&lt;unistd.h&gt;\u4e2d\u5b9a\u4e49\u3002<br>\u4f5c\u4e3a\u5bf9\u6bd4\uff0cISO C\u89c4\u5b9a\u7684\u6807\u51c6\u5e93stdin,stdout,stderr\u662f\u6587\u4ef6\u6307\u9488\u3002<\/p>\n\n\n\n<h1 class=\"wp-block-heading\" id=\"opene5928copenate587bde695b0-1\"><span class=\"ez-toc-section\" id=\"open%E5%92%8Copenat%E5%87%BD%E6%95%B0\"><\/span>open\u548copenat\u51fd\u6570<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<pre class=\"wp-block-code\"><code class=\"\">#include &lt;fcntl.h&gt;\n\nint open(const char *path, int oflag, ... <em>\/* mode_t mode *\/<\/em> );\n\nint openat(int fd, const char *path, int oflag, ... <em>\/* mode_t mode *\/<\/em> );\n<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u53ea\u6709\u521b\u5efa\u6587\u4ef6\u65f6\u624d\u4f1a\u9700\u8981\u6700\u540e\u7684mode\u53c2\u6570\u3002<br>\u56e0\u4e3a\u6bcf\u6b21open\u65f6\u8fd4\u56de\u7684\u603b\u662f\u6700\u5c0f\u7684\u53ef\u7528\u6587\u4ef6\u63cf\u8ff0\u7b26\uff0c\u56e0\u6b64\u53ef\u4ee5\u7528\u5173\u95edSTDIN_FILENO\u3001STDOUT_FILENO\u3001STDERR_FILENO\uff0c\u7136\u540e\u518d\u6253\u5f00\u65b0\u7684\u6587\u4ef6\u63cf\u8ff0\u7b26\u7684\u65b9\u5f0f\u91cd\u5b9a\u5411\u6807\u51c6\u8f93\u5165\u8f93\u51fa\u4ee5\u53castderr\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">openat\u4e0eopen\u7684\u4e0d\u540c\u4e4b\u5904\uff1a<\/p>\n\n\n\n<ol class=\"wp-block-list\"><li>\u5f53openat\u7684path\u662f\u7edd\u5bf9\u8def\u5f84\u65f6\uff0cfd\u88ab\u5ffd\u7565\uff1b<\/li><li>\u5f53openat\u7684path\u4e0d\u662f\u7edd\u5bf9\u8def\u5f84\u65f6\uff0c\u90a3\u4e48\u5c31\u5728fd\u6240\u4ee3\u8868\u7684\u76ee\u5f55\u4e0b\u641c\u5bfb\u6b64path\uff1b<\/li><li>\u5f53openat\u7684path\u662f\u76f8\u5bf9\u8def\u5f84\u4e14fd\u4e3a\u7279\u6b8a\u503cAT_FDCWD\u65f6\uff0c\u5728\u5f53\u524d\u5de5\u4f5c\u76ee\u5f55\u4e0b\u641c\u5bfbpath\uff1b<\/li><\/ol>\n\n\n\n<p class=\"wp-block-paragraph\">openat\u89e3\u51b3\u7684\u4e24\u4e2a\u95ee\u9898\uff1a<\/p>\n\n\n\n<ol class=\"wp-block-list\"><li>\u591a\u7ebf\u7a0b\u60c5\u666f\u4e0b\u53ef\u7528\u8ba9\u4e0d\u540c\u7ebf\u7a0b\u6709\u4e0d\u540c\u7684\u5f53\u524d\u5de5\u4f5c\u76ee\u5f55\uff1b<\/li><li>\u907f\u514dtime-of-check-to-time-of-use(TOCTTOU)\u9519\u8bef\u3002<\/li><\/ol>\n\n\n\n<h1 class=\"wp-block-heading\" id=\"create587bde695b0-1\"><span class=\"ez-toc-section\" id=\"creat%E5%87%BD%E6%95%B0\"><\/span>creat\u51fd\u6570<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<pre class=\"wp-block-code\"><code class=\"\">#include &lt;fcntl.h&gt;\n\nint creat(const char *path, mode_t mode);\n<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u7b49\u4ef7\u4e8e\u8c03\u7528<code>open(path, O_WRONLY | O_CREAT | O_TRUNC, mode);<\/code>\u3002<br>\u6bcf\u6b21open\u90fd\u4f1a\u5efa\u7acb\u4e00\u4e2a\u65b0\u7684file table entry\u3002<\/p>\n\n\n\n<h1 class=\"wp-block-heading\" id=\"closee587bde695b0-1\"><span class=\"ez-toc-section\" id=\"close%E5%87%BD%E6%95%B0\"><\/span>close\u51fd\u6570<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<pre class=\"wp-block-code\"><code class=\"\">#include &lt;unistd.h&gt;\n\nint close(int fd);\n<\/code><\/pre>\n\n\n\n<h1 class=\"wp-block-heading\" id=\"lseeke587bde695b0-1\"><span class=\"ez-toc-section\" id=\"lseek%E5%87%BD%E6%95%B0\"><\/span>lseek\u51fd\u6570<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<pre class=\"wp-block-code\"><code class=\"\">#include &lt;unistd.h&gt;\n\noff_t lseek(int fd, off_t offset, int whence);\n<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">whence\u53ef\u53d6\u503c\uff1aSEEK_SET\u3001SEEK_CUR\u3001SEEK_END\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">lseek\u7684\u8fd4\u56de\u503c\u8868\u793a\u64cd\u4f5c\u6210\u529f\u540e\u7684offset\uff0c\u56e0\u6b64\u53ef\u7528seek zero bytes\u7684\u65b9\u5f0f\u5224\u65ad\u5f53\u524d\u7684\u6587\u4ef6offset\u3002\u4f46\u662f\u5bf9\u4e8epipe\uff0cFIFO\u548c\u5957\u63a5\u5b57\uff0clseek\u64cd\u4f5c\u662f\u4e0d\u5141\u8bb8\u7684\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u5728Intel x86\u5904\u7406\u5668\u4e0a\u7684FreeBSD\u7684\/dev\/kmem\u6587\u4ef6\uff0cfile offset\u662f\u53ef\u7528\u4e3a\u8d1f\u7684\uff0c\u6240\u4ee5\u5224\u65adlseek\u8fd4\u56de\u503c\u4e00\u5b9a\u548c-1\u8fdb\u884c\u6bd4\u8f83\uff0c\u800c\u4e0d\u662f\u4ec5\u5224\u65ad\u662f\u5426\u5c0f\u4e8e0\u3002<br>lseek\u53ea\u662f\u4fee\u6539file offset\uff0c\u5e76\u4e0d\u8fdb\u884c\u5b9e\u9645\u4e0a\u7684I\/O\u64cd\u4f5c\u3002<br>file offset\u53ef\u4ee5\u88ab\u8bbe\u7f6e\u5f97\u6bd4\u5f53\u524d\u6587\u4ef6\u5927\u5c0f\u5927\uff0c\u7d27\u63a5\u7740\u7684\u5199\u64cd\u4f5c\u4f1a\u76f8\u5e94\u7684\u5c06\u6587\u4ef6\u6269\u5927(\u8fd9\u4e2a\u6587\u4ef6\u7531\u6b64\u6709\u4e86\u4e00\u4e2afile hole)\uff0c\u4f46\u662f\u6587\u4ef6\u7cfb\u7edf\u662f\u5426\u771f\u6b63\u7684\u5728\u78c1\u76d8\u4e0a\u5f00\u8f9f\u7a7a\u95f4\u6765\u4fdd\u5b58\u8fd9\u4e2d\u95f4\u51ed\u7a7a\u591a\u51fa\u7684\u90e8\u5206\u53d6\u51b3\u4e8e\u5177\u4f53\u7684\u6587\u4ef6\u7cfb\u7edf\u5b9e\u73b0\u3002<\/p>\n\n\n\n<h1 class=\"wp-block-heading\" id=\"reade587bde695b0-1\"><span class=\"ez-toc-section\" id=\"read%E5%87%BD%E6%95%B0\"><\/span>read\u51fd\u6570<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<pre class=\"wp-block-code\"><code class=\"\">#include &lt;unistd.h&gt;\n\nssize_t read(int fd, void *buf, size_t nbytes);\n<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">file offset\u7684\u66f4\u65b0\u4f1a\u65e9\u4e8eread\u8fd4\u56de\u5b9e\u9645\u8bfb\u53d6\u7684\u6570\u636e\u3002<\/p>\n\n\n\n<h1 class=\"wp-block-heading\" id=\"writee587bde695b0-1\"><span class=\"ez-toc-section\" id=\"write%E5%87%BD%E6%95%B0\"><\/span>write\u51fd\u6570<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<pre class=\"wp-block-code\"><code class=\"\">#include &lt;unistd.h&gt;\n\nssize_t write(int fd, const void *buf, size_t nbytes);\n<\/code><\/pre>\n\n\n\n<h1 class=\"wp-block-heading\" id=\"file-sharing-1\"><span class=\"ez-toc-section\" id=\"File_Sharing\"><\/span>File Sharing<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"883\" height=\"543\" src=\"https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/apiue_file-table-entry1.png\" alt=\"\" class=\"wp-image-955\" srcset=\"https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/apiue_file-table-entry1.png 883w, https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/apiue_file-table-entry1-300x184.png 300w, https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/apiue_file-table-entry1-768x472.png 768w, https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/apiue_file-table-entry1-670x412.png 670w\" sizes=\"auto, (max-width: 883px) 100vw, 883px\" \/><\/figure>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"877\" height=\"632\" src=\"https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/apiue_file-table-entry2.png\" alt=\"\" class=\"wp-image-956\" srcset=\"https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/apiue_file-table-entry2.png 877w, https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/apiue_file-table-entry2-300x216.png 300w, https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/apiue_file-table-entry2-768x553.png 768w, https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/apiue_file-table-entry2-670x483.png 670w\" sizes=\"auto, (max-width: 877px) 100vw, 877px\" \/><\/figure>\n\n\n\n<h1 class=\"wp-block-heading\" id=\"atomic-operations-1\"><span class=\"ez-toc-section\" id=\"Atomic_Operations\"><\/span>Atomic Operations<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<ul class=\"wp-block-list\"><li>\u5728\u6253\u5f00\u6587\u4ef6\u65f6\u5982\u679c\u8bbe\u7f6e\u4e86O_APPEND\u6807\u5fd7\uff0c\u90a3\u4e48\u5728\u4ee5\u540e\u7684\u6bcf\u6b21\u5199\u64cd\u4f5c\u7684\u65f6\u5019\uff0c\u7cfb\u7edf\u90fd\u4f1a\u5148\u81ea\u52a8\u5c06file table entry\u7684file offset\u8bbe\u7f6e\u4e3a\u6587\u4ef6\u672b\u5c3e\uff0c\u7136\u540e\u518d\u8fdb\u884c\u5199\u64cd\u4f5c\uff0c\u4e14\u8fd9\u79cd\u5b9a\u4f4d\u5230\u6587\u4ef6\u672b\u5c3e\u518d\u5199\u5165\u7684\u64cd\u4f5c\u662f\u539f\u5b50\u6027\u7684\uff0c\u9632\u6b62\u4e86\u591a\u4e2a\u8fdb\u7a0b\u5f80\u540c\u4e00\u4e2a\u6587\u4ef6\u91cc\u8ffd\u52a0\u5185\u5bb9\u65f6\u4e00\u4e2a\u8fdb\u7a0b\u7684\u5199\u5165\u8986\u76d6\u5176\u4ed6\u8fdb\u7a0b\u7684\u5199\u5165\u95ee\u9898\u3002<\/li><li>\u7c7b\u4f3c\u7684\u539f\u5b50\u64cd\u4f5c\u8fd8\u6709\u68c0\u67e5\u6587\u4ef6\u662f\u5426\u5b58\u5728\uff0c\u4e14\u4e0d\u5b58\u5728\u5c31\u521b\u5efa\u8be5\u6587\u4ef6\u8fd9\u79cd\u64cd\u4f5c\u3002\u8fd9\u9700\u8981\u901a\u8fc7open\u7684\u65f6\u5019\u5e26\u4e0aO_CREAT\u548cO_EXCL\u9009\u9879\u6765\u5b8c\u6210\u3002<\/li><li>\u4e3a\u4e86\u907f\u514d\u591a\u7ebf\u7a0b\u60c5\u666f\u4e0b\u591a\u4e2a\u7ebf\u7a0b\u5171\u4eab\u4e00\u4e2afile offset\u7684\u56f0\u6270\uff0c\u53ef\u4ee5\u4f7f\u7528pread\u548cpwrite\u51fd\u6570\u3002<\/li><\/ul>\n\n\n\n<pre class=\"wp-block-code\"><code class=\"\">#include &lt;unistd.h&gt;\n\nssize_t pread(int fd, void *buf, size_t nbytes, off_t offset);\n\nssize_t pwrite(int fd, const void *buf, size_t nbytes, off_t offset);\n<\/code><\/pre>\n\n\n\n<h1 class=\"wp-block-heading\" id=\"dupe5928cdup2e587bde695b0-1\"><span class=\"ez-toc-section\" id=\"dup%E5%92%8Cdup2%E5%87%BD%E6%95%B0\"><\/span>dup\u548cdup2\u51fd\u6570<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<pre class=\"wp-block-code\"><code class=\"\">#include &lt;unistd.h&gt;\n\nint dup(int fd);\n\nint dup2(int fd, int fd2);\n<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">dup\u8fd4\u56de\u7684\u603b\u662f\u6700\u5c0f\u53ef\u7528\u6587\u4ef6\u63cf\u8ff0\u7b26\u4e14\u4f1a\u6e05\u9664close-on-exec\u6587\u4ef6\u63cf\u8ff0\u7b26\u6807\u5fd7\u4f4d\u3002<br>\u5bf9\u4e8edup2\uff1a<\/p>\n\n\n\n<ul class=\"wp-block-list\"><li>\u5982\u679cfd2\u5df2\u7ecf\u88ab\u6253\u5f00\uff0c\u90a3\u4e48fd2\u4f1a\u5148\u88ab\u5173\u95ed\u3002\u7136\u540e\u8ba9fd2\u4e0efd\u6307\u5411\u540c\u4e00\u4e2afile table entry\uff0c\u5e76\u4e14\u6e05\u9664fd2\u7684FD_CLOEXEC\u6807\u5fd7\u4f4d\u3002<\/li><li>\u5982\u679cfd2\u7b49\u4e8efd\uff0c\u90a3\u4e48\u5c31\u4e0d\u5173\u95edfd2\uff0c\u4e5f\u4e0d\u4f1a\u6e05\u9664FD_CLOEXEC\u6807\u5fd7\u4f4d\u3002<\/li><\/ul>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"885\" height=\"374\" src=\"https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/apiue_dup.png\" alt=\"\" class=\"wp-image-957\" srcset=\"https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/apiue_dup.png 885w, https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/apiue_dup-300x127.png 300w, https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/apiue_dup-768x325.png 768w, https:\/\/blog.cauchyschwarz.com\/wp-content\/uploads\/2021\/12\/apiue_dup-670x283.png 670w\" sizes=\"auto, (max-width: 885px) 100vw, 885px\" \/><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">dup2\u57fa\u672c\u7b49\u6548\u4e8e\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code class=\"\">close(fd2);\nfcntl(fd, F_DUPFD, fd2);\n<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u4f46\u662f\u4e0d\u540c\u4e4b\u5904\u5728\u4e8edup2\u662f\u4e00\u4e2a\u539f\u5b50\u64cd\u4f5c\u3002<\/p>\n\n\n\n<h1 class=\"wp-block-heading\" id=\"syncfsyncfdatasynce587bde695b0-1\"><span class=\"ez-toc-section\" id=\"sync%E3%80%81fsync%E3%80%81fdatasync%E5%87%BD%E6%95%B0\"><\/span>sync\u3001fsync\u3001fdatasync\u51fd\u6570<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<pre class=\"wp-block-code\"><code class=\"\">#include &lt;unistd.h&gt;\n\nint fsync(int fd);\nint fdatasync(int fd);\n\nvoid sync(void);\n<\/code><\/pre>\n\n\n\n<h1 class=\"wp-block-heading\" id=\"fcntle587bde695b0-1\"><span class=\"ez-toc-section\" id=\"fcntl%E5%87%BD%E6%95%B0\"><\/span>fcntl\u51fd\u6570<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<pre class=\"wp-block-code\"><code class=\"\">#include &lt;fcntl.h&gt;\n\nint fcntl(int fd, int cmd, ... <em>\/* int arg *\/<\/em> );\n<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">fcntl\u7528\u4e8e\u6539\u53d8\u5df2\u7ecf\u6253\u5f00\u6587\u4ef6\u7684\u5c5e\u6027\u3002fcntl\u6709\u4e94\u79cd\u7528\u9014\uff1a<\/p>\n\n\n\n<ol class=\"wp-block-list\"><li>\u590d\u5236\u6587\u4ef6\u63cf\u8ff0\u7b26(cmd=F_DUPFD\u6216\u8005F_DUPFD_CLOEXEC)<\/li><li>\u8bfb\u53d6\/\u8bbe\u7f6e\u6587\u4ef6\u63cf\u8ff0\u7b26\u6807\u5fd7\u4f4d(cmd=F_GETFD\u6216F_SETFD)<\/li><li>\u8bfb\u53d6\/\u8bbe\u7f6e\u6587\u4ef6\u72b6\u6001\u6807\u5fd7\u4f4d(cmd=F_GETFL\u6216F_SETFL)<\/li><li>\u8bfb\u53d6\/\u8bbe\u7f6e\u5f02\u6b65I\/O\u7684owner(cmd=F_GETOWN\u6216F_SETOWN)<\/li><li>\u8bfb\u53d6\/\u8bbe\u7f6erecord locks(cmd=F_GETLK,F_SETLK,\u6216F_SETLKW)<\/li><\/ol>\n\n\n\n<p class=\"wp-block-paragraph\">\u6ce8\u610ffile descriptor flag\u6307\u7684\u662fFD_CLOEXEC(\u76ee\u524d\u5b9e\u73b0\u53ea\u6709\u8fd9\u4e2a\u6807\u5fd7\u4f4d)\uff0c\u800cfile status flag\u6307\u7684\u662f\u6253\u5f00\u6587\u4ef6\u65f6\u4f20\u5165\u7684\u90a3\u4e9bO_RDONLY\u3001O_APPEND\u3001O_SYNC\u8fd9\u7c7b\u6807\u5fd7\u4f4d\u3002<br>\u53e6\u4e00\u4e2a\u9700\u8981\u6ce8\u610f\u7684\u5730\u65b9\u662f\u4f7f\u7528F_GETFL\u6807\u5fd7\u65f6\uff0c\u8fd4\u56de\u7684file status flag\uff1aO_RDONLY\u3001O_WRONLY\u3001O_RDWR\u3001O_EXEC\u3001O_SEARCH\u8fd9\u4e2a\u51e0\u4e2aflag\u5e76\u4e0d\u662f\u72ec\u7acb\u53ef\u4ee5\u6309\u4f4d\u6d4b\u8bd5\u7684(\u6bd4\u5982O_RDONLY\u3001O_WRONLY\u3001O_RDWR\u7684\u503c\u7ecf\u5e38\u662f0,1,2)\u3002\u6240\u4ee5\u6211\u4eec\u9700\u8981\u5c06fcntl\u7684\u8fd4\u56de\u503c\u4e0eO_ACCMODE\u6309\u4f4d\u4e0e\uff0c\u7136\u540e\u518d\u5224\u65ad\u548c\u8fd9\u51e0\u4e2a\u503c\u4e2d\u7684\u54ea\u4e00\u4e2a\u76f8\u7b49\u3002<\/p>\n\n\n\n<h1 class=\"wp-block-heading\" id=\"ioctle587bde695b0e69687e4bbb6-1\"><span class=\"ez-toc-section\" id=\"ioctl%E5%87%BD%E6%95%B0%E6%96%87%E4%BB%B6\"><\/span>ioctl\u51fd\u6570\u6587\u4ef6<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">\u64cd\u7eb5\u4e00\u4e9b\u7279\u6b8a\u6587\u4ef6\u8bbe\u5907\u65f6\u7ecf\u5e38\u4f1a\u7528\u5230ioctl\u51fd\u6570\uff0c\u6bd4\u5982\u786c\u76d8\u3001socket\u3001\u78c1\u5e26\u3001terminal\u7b49\u3002\u8bb0\u5f97\u4ee5\u524d\u5199oss\u7a0b\u5e8f\u65f6\u4e5f\u7ecf\u5e38\u7528\u8fd9\u4e2a\u51fd\u6570\u3002<\/p>\n\n\n\n<h1 class=\"wp-block-heading\" id=\"devfde69687e4bbb6-1\"><span class=\"ez-toc-section\" id=\"devfd%E6%96%87%E4%BB%B6\"><\/span>\/dev\/fd\u6587\u4ef6<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">\u5927\u610f\u5c31\u662f\/dev\/fd\/n\u6587\u4ef6\u5c31\u4ee3\u8868\u4e86\u76f8\u5e94\u7684\u6587\u4ef6\u63cf\u8ff0\u7b26\u3002<\/p>\n\n\n\n<h1 class=\"wp-block-heading\" id=\"exercises-1\"><span class=\"ez-toc-section\" id=\"Exercises\"><\/span>Exercises<span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"wp-block-paragraph\">2.\u8981\u4e0d\u7528fcntl\u5b9e\u73b0dup2\u3002\u4f46\u662fdup2\u8981\u6c42\u4e24\u4e2a\u6587\u4ef6\u63cf\u8ff0\u7b26\u6307\u5411\u540c\u4e00\u4e2afile table entry\uff0c\u800copen\u51fd\u6570\u4f1a\u521b\u5efa\u65b0\u7684file table entry\u3002\u552f\u4e00\u60f3\u5230\u7684\u529e\u6cd5\u662f\u5229\u7528dup\u51fd\u6570\u8fd4\u56de\u5f53\u524d\u6700\u5c0f\u53ef\u7528\u6587\u4ef6\u63cf\u8ff0\u7b26\u7684\u7279\u6027\uff0c\u4e0d\u505c\u7528dup\u51fd\u6570\u521b\u5efa\u65b0\u7684\u6587\u4ef6\u63cf\u8ff0\u7b26\u76f4\u5230\u8fd4\u56de\u7684\u6587\u4ef6\u63cf\u8ff0\u7b26\u5927\u4e8e\u7b49\u4e8e\u60f3\u5f97\u5230\u7684\u6587\u4ef6\u63cf\u8ff0\u7b26\u3002\u5bf9\u4e8e\u8fd9\u4e2a\u5927\u4e8e\u7b49\u4e8e\u6307\u5b9a\u503c\u7684fd\uff0c\u5982\u679c\u5b83\u6b63\u597d\u7b49\u4e8e\u6307\u5b9a\u503c\uff0c\u8bf4\u660e\u8fd9\u4e2a\u503c\u4ee3\u8868\u7684\u6587\u4ef6\u63cf\u8ff0\u7b26\u4e4b\u524d\u662f\u6ca1\u6709\u6253\u5f00\u7684\uff0c\u5426\u5219\u8bf4\u660e\u8fd9\u4e2a\u503c\u4ee3\u8868\u7684\u6587\u4ef6\u63cf\u8ff0\u7b26\u662f\u5df2\u7ecf\u88ab\u6253\u5f00\u8fc7\u4e86\u7684\uff0c\u90a3\u4e48\u6211\u4eec\u5c31\u5148\u5173\u95ed\u8fd9\u4e2a\u503c\u5bf9\u5e94\u7684\u6587\u4ef6\u63cf\u8ff0\u7b26\uff0c\u7136\u540e\u518ddup\u4e00\u6b21\uff0c\u90a3\u4e48\u8fd4\u56de\u7684\u6587\u4ef6\u63cf\u8ff0\u7b26\u5c31\u662f\u8fd9\u4e2a\u6307\u5b9a\u503c\u4e86\u3002\u6700\u540e\u5173\u6389\u90a3\u4e9b\u88ab\u6211\u4eec\u6253\u5f00\u4f46\u662f\u4e0d\u7528\u7684\u6587\u4ef6\u63cf\u8ff0\u7b26\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">5.\u9898\u76ee\u7701\u7565\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u6d4b\u8bd5\u7a0b\u5e8f\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code class=\"\">#include &lt;unistd.h&gt;\n\nint main(int argc, char **argv) {\n\n\tchar hello1[] = \"hello stdout\";\n\tchar hello2[] = \"hello stderr\";\n\n\twrite(STDOUT_FILENO, hello1, sizeof(hello1));\n\twrite(STDERR_FILENO, hello2, sizeof(hello2));\n\n\treturn 0;\n}\n<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u7ed3\u8bba\u5c31\u662f\uff1a1.<code>&gt;<\/code>\u7b26\u53f7\u53ea\u66f4\u6539\u4e86stdout\u6307\u5411\u7684\u6587\u4ef6\uff1b2.<code>digit1 &gt;&amp; digit2<\/code>\u8fd9\u79cd\u66f4\u6539\u65b9\u5f0f\u5b9e\u9645\u4e0a\u7684\u64cd\u4f5c\u662f\u8ba9\u6587\u4ef6\u63cf\u8ff0\u7b26digit2\u6307\u5411\u6587\u4ef6\u63cf\u8ff0\u7b26digit1\u6307\u5411\u7684\u6587\u4ef6(\u6307\u5411\u540c\u4e00\u4e2afile table entry)\u3002<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">6.If you open a file for read\u2013write with the append flag, can you still read from anywhere in the file using lseek? Can you use lseek to replace existing data in the file? Write a program to verify this.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u6d4b\u8bd5\u7a0b\u5e8f\uff1a<\/p>\n\n\n\n<pre class=\"wp-block-code\"><code class=\"\">#include &lt;stdio.h&gt;\n#include &lt;unistd.h&gt;\n#include &lt;fcntl.h&gt;\n\nint main(int argc, char **argv) {\n\tchar hello[] = \"hello world\";\n\tint fd = open(\"test.bin\", O_RDWR | O_APPEND);\n\tif (fd &lt; 0) {\n\t\tprintf(\"open file failed!\\n\");\n\t\treturn -4;\n\t}\n\tint n_write = write(fd, hello, sizeof(hello));\n\tif (n_write != sizeof(hello)) {\n\t\tprintf(\"write failed!\\n\"\n\t\t\t\t\"write %d bytes\\n\", n_write);\n\t\treturn -1;\n\t}\n\n\toff_t p_seek = lseek(fd, 0, SEEK_SET);\n\tif (p_seek != 0) {\n\t\tprintf(\"lseek failed!\\n\"\n\t\t\t\t\"lseek returns %ld\\n\", p_seek);\n\t\treturn -2;\n\t}\n\n\tchar buf[sizeof(hello)];\n\tfor (int i = 0; i &lt; sizeof(hello); i++) {\n\t\tbuf[i] = 0;\n\t}\n\n\tint n_read = read(fd, buf, sizeof(hello));\n\tif (n_read != sizeof(hello)) {\n\t\tprintf(\"read after lseek failed!\\n\"\n\t\t\t\t\"read %d bytes\\n\", n_read);\n\t\treturn -3;\n\t}\n\tprintf(\"read content:%s\\n\", buf);\n\n\tchar hostile[] = \"hostile!\";\n\tp_seek = lseek(fd, 0, SEEK_SET);\n\tif (p_seek != 0) {\n\t\tprintf(\"lseek failed!\\n\"\n\t\t\t\t\"lseek returns %ld\\n\", p_seek);\n\t\treturn -2;\n\t}\n\n\tn_write = write(fd, hostile, sizeof(hostile));\n\tif (n_write != sizeof(hostile)) {\n\t\tprintf(\"write failed after lseek!\\n\"\n\t\t\t\t\"write %d bytes\\n\", n_write);\n\t}\n\n\n\treturn 0;\n}\n<\/code><\/pre>\n\n\n\n<p class=\"wp-block-paragraph\">\u5728\u6211\u7684Ubuntu\u4e0a\uff0clseek\u548cread\u3001write\u64cd\u4f5c\u90fd\u53ef\u4ee5\u6210\u529f\uff0c\u4f46\u662f\u7b2c\u4e8c\u6b21write\u7684\u64cd\u4f5c\u662f\u63a5\u7740\u5728hello world!\u540e\u9762\u5199\u7684\uff0c\u800c\u4e0d\u662f\u5728lseek\u91cd\u5b9a\u4f4d\u7684\u6587\u4ef6\u5f00\u5934\u3002\u8fd9\u5370\u8bc1\u4e86\u4e66\u524d\u9762\u6240\u8bf4\u7684\u5e26O_APPEND\u6807\u5fd7\u6253\u5f00\u6587\u4ef6\u65f6\uff0c\u6bcf\u6b21\u5199\u64cd\u4f5c\u4e4b\u524d\u90fd\u4f1a\u5c06\u76f8\u5e94\u7684file offset\u7f6e\u4e3a\u6587\u4ef6\u672b\u5c3e\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u6587\u4ef6\u63cf\u8ff0\u7b26 \u5185\u6838\u901a\u8fc7\u6587\u4ef6\u63cf\u8ff0\u7b26\u6765\u5f15\u7528\u6253\u5f00\u7684\u6587\u4ef6\u3002\u6bcf\u4e2a\u8fdb\u7a0b\u6700\u591a\u80fd\u540c\u65f6\u6253\u5f00OPEN_MAX\u4e2a\u6587\u4ef6\u63cf\u8ff0\u7b26\u3002\u4e00\u822c\u524d3\u4e2a\u662f\uff1aSTDIN_FILENO(0), STDOUT_FILENO(1), STDERR_F&#46;&#46;&#46;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[10,6],"tags":[109],"class_list":["post-954","post","type-post","status-publish","format-standard","hentry","category-10","category-6","tag-apiue"],"_links":{"self":[{"href":"https:\/\/blog.cauchyschwarz.com\/index.php?rest_route=\/wp\/v2\/posts\/954","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blog.cauchyschwarz.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.cauchyschwarz.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.cauchyschwarz.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.cauchyschwarz.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=954"}],"version-history":[{"count":1,"href":"https:\/\/blog.cauchyschwarz.com\/index.php?rest_route=\/wp\/v2\/posts\/954\/revisions"}],"predecessor-version":[{"id":958,"href":"https:\/\/blog.cauchyschwarz.com\/index.php?rest_route=\/wp\/v2\/posts\/954\/revisions\/958"}],"wp:attachment":[{"href":"https:\/\/blog.cauchyschwarz.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=954"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.cauchyschwarz.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=954"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.cauchyschwarz.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=954"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}