\u865a\u62df\u6587\u4ef6\u7cfb\u7edf\uff08Virtual Filesystem Switch\uff0cVFS\uff09\u4e3a\u5404\u79cd\u6587\u4ef6\u7cfb\u7edf\u63d0\u4f9b\u4e86\u4e00\u4e2a\u901a\u7528\u7684\u63a5\u53e3\uff0c\u5b83\u4f7f\u5f97\u4e0a\u5c42\u8fdb\u7a0b\u5728\u8fdb\u884c\u4e0e\u6587\u4ef6\u7cfb\u7edf\u76f8\u5173\u7684\u64cd\u4f5c\u65f6\u53ef\u4ee5\u4f7f\u7528\u540c\u4e00\u7ec4\u7cfb\u7edf\u8c03\u7528\uff0c\u4f46\u662f\u7cfb\u7edf\u8c03\u7528\u5728\u5185\u6838\u4e2d\u53ef\u4ee5\u6839\u636e\u4e0d\u540c\u7684\u6587\u4ef6\u7cfb\u7edf\u6267\u884c\u4e0d\u540c\u7684\u64cd\u4f5c\u3002<\/p>\n
\u4e0e\u6587\u4ef6\u76f8\u5173\u7684\u57fa\u672c\u64cd\u4f5c\u51fd\u6570\u6709\uff1aopen\u3001read\u3001write\u548cclose\uff0c\u672c\u6587\u5c06\u7ed3\u5408\u5185\u6838\u6e90\u4ee3\u7801\u5206\u6790\u8fd9\u4e9b\u51fd\u6570\u5728\u865a\u62df\u6587\u4ef6\u7cfb\u7edf\u4e2d\u7684\u5b9e\u73b0\u3002<\/p>\n
open\u7cfb\u7edf\u8c03\u7528\u7684\u4f5c\u7528\u662f\u6253\u5f00\u6216\u521b\u5efa\u4e00\u4e2a\u6587\u4ef6\uff0c\u5e76\u4e14\u8fd4\u56de\u8be5\u6587\u4ef6\u7684\u6587\u4ef6\u63cf\u8ff0\u7b26\u3002\u5728\u5185\u6838\u4e2d\uff0copen\u7cfb\u7edf\u8c03\u7528\u4e3b\u8981\u5b8c\u6210\u7684\u5de5\u4f5c\u662f\u4e3a\u6b64\u6b21\u6253\u5f00\u7684\u6587\u4ef6\u521b\u5efafile\u5bf9\u8c61\uff0c\u8be5\u5bf9\u8c61\u5728fd_array\u6570\u7ec4\u4e2d\u7684\u7d22\u5f15\u503c\u4e3a\u8fd4\u56de\u7528\u6237\u7a7a\u95f4\u7684\u6587\u4ef6\u63cf\u8ff0\u7b26\u3002<\/p>\n
open\u7cfb\u7edf\u8c03\u7528\u5bf9\u5e94\u7684\u7cfb\u7edf\u8c03\u7528\u670d\u52a1\u4f8b\u7a0b\u4e3asys_open\uff0c\u4e0d\u8fc7\u76ee\u524d\u5185\u6838\u5df2\u7ecf\u7edf\u4e00\u4f7f\u7528SYSCALL_DEFINEn\u8fd9\u79cd\u65b9\u5f0f\u5bf9\u7cfb\u7edf\u8c03\u7528\u670d\u52a1\u4f8b\u7a0b\u8fdb\u884c\u5b9a\u4e49\u3002\u5728open\u7cfb\u7edf\u8c03\u7528\u670d\u52a1\u4f8b\u7a0b\u4e2d\u53c8\u76f4\u63a5\u8c03\u7528\u4e86do_sys_open\u51fd\u6570\uff0c\u5b83\u662f\u6253\u5f00\u52a8\u4f5c\u7684\u4e3b\u4f53\u51fd\u6570\u3002<\/p>\n
\r\nlong do_sys_open(int dfd, const char __user *filename, int flags, int mode)\r\n{\r\n char *tmp = getname(filename);\r\n int fd = PTR_ERR(tmp);\r\n\r\n if (!IS_ERR(tmp)) {\r\n fd = get_unused_fd_flags(flags);\r\n if (fd >= 0) {\r\n struct file *f = do_filp_open(dfd, tmp, flags, mode, 0);\r\n if (IS_ERR(f)) {\r\n put_unused_fd(fd);\r\n fd = PTR_ERR(f);\r\n } else {\r\n fsnotify_open(f->f_path.dentry);\r\n fd_install(fd, f);\r\n }\r\n }\r\n putname(tmp);\r\n }\r\n return fd;\r\n}<\/pre>\n\u7528\u6237\u8fdb\u7a0b\u4f7f\u7528open\u6253\u5f00\u6587\u4ef6\u65f6\u5c06\u4f20\u9012\u6587\u4ef6\u8def\u5f84filename\uff0c\u56e0\u6b64\u8be5\u51fd\u6570\u7b2c\u4e00\u6b65\u5148\u901a\u8fc7getname\u51fd\u6570\u4ece\u7528\u6237\u7a7a\u95f4\u8bfb\u53d6\u6587\u4ef6\u8def\u5f84\u5230\u5185\u6838\u7a7a\u95f4\uff0c\u6682\u5b58\u5230tmp\u3002\u901a\u8fc7get_unused_fd_flags\u51fd\u6570\u5728\u5f53\u524d\u8fdb\u7a0b\u7684fd_array\u6570\u636e\u4e2d\u627e\u5230\u4e00\u4e2a\u4f55\u65f6\u7684\u4f4d\u7f6e\uff0c\u5e76\u8fd4\u56de\u5176\u7d22\u5f15\u3002<\/p>\n
\u63a5\u4e0b\u6765\u901a\u8fc7do_filp_open\u51fd\u6570\u6267\u884c\u6253\u5f00\u6587\u4ef6\u7684\u6838\u5fc3\u64cd\u4f5c\uff1a\u6839\u636e\u7cfb\u7edf\u8c03\u7528\u4e2d\u7684\u6807\u5fd7\u53c2\u6570flags\u548c\u8bbf\u95ee\u6a21\u5f0fmode\u8bbe\u7f6e\u76f8\u5e94\u7684\u5c40\u90e8\u53d8\u91cf\u4ee5\u4fbf\u540e\u7eed\u4f7f\u7528\uff1b\u6839\u636e\u8981\u6253\u5f00\u6587\u4ef6\u7684\u8def\u5f84tmp\u5bfb\u627e\u5176inode\u8282\u70b9\uff0c\u5982\u679c\u8be5inode\u8282\u70b9\u4e0d\u5b58\u5728\u5e76\u4e14\u8bbe\u7f6e\u4e86O_CREATE\u6807\u5fd7\u5219\u5728\u78c1\u76d8\u4e0a\u521b\u5efa\u4e00\u4e2a\u65b0\u7684\u78c1\u76d8\u7d22\u5f15\u8282\u70b9\uff1b\u5206\u914d\u4e00\u4e2a\u65b0\u7684\u6587\u4ef6\u5bf9\u8c61\uff0c\u5e76\u6839\u636e\u7cfb\u7edf\u8c03\u7528\u4f20\u9012\u7684\u6807\u5fd7\u548c\u8bbf\u95ee\u6a21\u5f0f\u8bbe\u7f6e\u6587\u4ef6\u5bf9\u8c61\u7684f_flags\u548cf_mode\u5b57\u6bb5\uff1b\u4f7f\u7528\u7d22\u5f15\u8282\u70b9\u7684i_fop\u5b57\u6bb5\u521d\u59cb\u5316\u6587\u4ef6\u5bf9\u8c61\u7684f_op\u5b57\u6bb5\uff1b\u5c06\u8be5\u6587\u4ef6\u5bf9\u8c61\u63d2\u5165\u5230\u8d85\u7ea7\u5757\u6307\u5411\u7684\u6253\u5f00\u6587\u4ef6\u94fe\u8868\u4e2d\uff1b\u5982\u679c\u6587\u4ef6\u5bf9\u8c61\u64cd\u4f5c\u51fd\u6570\u96c6\u4e2d\u7684open\u51fd\u6570\u88ab\u5b9a\u4e49\u5219\u8c03\u7528\u5b83\uff1b\u6700\u540e\u8fd4\u56de\u8fd9\u4e2a\u6587\u4ef6\u5bf9\u8c61\uff1b<\/p>\n
\u5982\u679c\u8fd9\u4e2a\u6587\u4ef6\u5bf9\u8c61\u521b\u5efa\u6210\u529f\uff0c\u5219\u901a\u8fc7fd_install\u51fd\u6570\u5c06\u8be5\u6587\u4ef6\u5bf9\u8c61\u8d4b\u503c\u5230fd_array\u6570\u7ec4\u7684\u7b2cfd\u4e2a\u5143\u7d20\u4e2d\u3002<\/p>\n
2.read()\u7684\u5b9e\u73b0<\/h3>\n
\u8bfb\u6587\u4ef6\u7cfb\u7edf\u8c03\u7528read()\u7684\u4f5c\u7528\u662f\u6839\u636e\u6587\u4ef6\u63cf\u8ff0\u7b26fd\u8bfb\u53d6\u6307\u5b9a\u957f\u5ea6size\u7684\u6570\u636e\u5230\u7f13\u51b2\u533abuf\u4e2d\u3002\u8be5\u7cfb\u7edf\u8c03\u7528\u7684\u5b9e\u73b0\u6d89\u53ca\u4e86\u5185\u6838\u4e2d\u5bf9I\/O\u8fdb\u884c\u5904\u7406\u7684\u5404\u4e2a\u5c42\u6b21\uff0c\u4f46\u662f\u5bf9\u4e8eVFS\u5c42\u6765\u8bf4\u5b9e\u73b0\u65b9\u6cd5\u6bd4\u8f83\u6e05\u6670\u3002<\/p>\n
\r\nSYSCALL_DEFINE3(read, unsigned int, fd, char __user *, buf, size_t, count)\r\n{\r\n struct file *file;\r\n ssize_t ret = -EBADF;\r\n int fput_needed;\r\n \r\n file = fget_light(fd, &fput_needed);\r\n if (file) {\r\n loff_t pos = file_pos_read(file);\r\n ret = vfs_read(file, buf, count, &pos);\r\n file_pos_write(file, pos);\r\n fput_light(file, fput_needed);\r\n }\r\n\r\n return ret;\r\n}\r\n<\/pre>\n\u5728read\u7cfb\u7edf\u8c03\u7528\u5bf9\u5e94\u7684\u670d\u52a1\u4f8b\u7a0b\u4e2d\uff0c\u9996\u5148\u4f7f\u7528fget_light\u51fd\u6570\u901a\u8fc7fd\u83b7\u53d6\u5bf9\u5e94\u7684\u6587\u4ef6\u5bf9\u8c61\uff1b\u518d\u901a\u8fc7file_pos_read\u51fd\u6570\u83b7\u53d6\u8bfb\u6587\u4ef6\u7684\u8d77\u59cb\u504f\u79fb\u91cf\uff0c\u5373\u6587\u4ef6\u5bf9\u8c61\u7684f_pos\u5b57\u6bb5\u7684\u503c\uff1b\u63a5\u7740\u901a\u8fc7vfs_read\u51fd\u6570\u8fdb\u884c\u8bfb\u64cd\u4f5c\uff1b\u901a\u8fc7file_pos_write\u51fd\u6570\u66f4\u65b0\u6587\u4ef6\u5f53\u524d\u7684\u504f\u79fb\u91cf\uff1b\u901a\u8fc7fput_light\u51fd\u6570\u91ca\u653e\u6587\u4ef6\u5bf9\u8c61\uff1b\u6700\u7ec8\u8fd4\u56devfs_read\u51fd\u6570\u7684\u8fd4\u56de\u503cret\uff0c\u8be5\u503c\u5219\u4e3a\u5b9e\u9645\u8bfb\u53d6\u6570\u636e\u7684\u957f\u5ea6\u3002<\/p>\n
read\u7cfb\u7edf\u670d\u52a1\u4f8b\u7a0b\u4e2d\u6700\u6838\u5fc3\u7684\u51fd\u6570\u5373\u4e3avfs_read\uff0c\u5b83\u7684\u4e3b\u8981\u5de5\u4f5c\u662f\u9009\u62e9\u4e00\u4e2a\u5177\u4f53\u7684\u8bfb\u64cd\u4f5c\u51fd\u6570\u3002\u5982\u679c\u5f53\u524d\u6587\u4ef6\u5bf9\u8c61\u64cd\u4f5c\u51fd\u6570\u96c6\u4e2d\u7684read\u94a9\u5b50\u51fd\u6570\uff08file->f_op->read\uff09\u88ab\u5b9e\u73b0\uff08\u901a\u5e38\u5728\u9a71\u52a8\u7a0b\u5e8f\u4e2d\u5b9e\u73b0\uff09\uff0c\u5219\u8c03\u7528\u5b83\u3002\u5426\u5219\u4f7f\u7528\u5185\u6838\u9ed8\u8ba4\u7684\u8bfb\u51fd\u6570do_sys_read\u3002<\/p>\n
\r\nssize_t vfs_read(struct file *file, char __user *buf, size_t count, loff_t *pos)\r\n{\r\n ssize_t ret;\r\n\r\n if (!(file->f_mode & FMODE_READ))\r\n return -EBADF;\r\n if (!file->f_op || (!file->f_op->read && !file->f_op->aio_read))\r\n return -EINVAL;\r\n if (unlikely(!access_ok(VERIFY_WRITE, buf, count)))\r\n return -EFAULT;\r\n\r\n ret = rw_verify_area(READ, file, pos, count);\r\n if (ret >= 0) {\r\n count = ret;\r\n if (file->f_op->read)\r\n ret = file->f_op->read(file, buf, count, pos);\r\n else\r\n ret = do_sync_read(file, buf, count, pos);\r\n if (ret > 0) {\r\n fsnotify_access(file->f_path.dentry);\r\n add_rchar(current, ret);\r\n }\r\n inc_syscr(current);\r\n }\r\n\r\n return ret;\r\n}\r\n<\/pre>\n\u4e8b\u5b9e\u4e0a\uff0cdo_sys_read\u51fd\u6570\u5728\u5185\u90e8\u8c03\u7528\u94a9\u5b50\u51fd\u6570aio_read\uff08file->f_op->aio_read\uff09\uff0c\u8be5\u94a9\u5b50\u51fd\u6570\u4e00\u822c\u6307\u5411\u5185\u6838\u5b9e\u73b0\u7684\u901a\u7528\u8bfb\u51fd\u6570generic_file_aio_read\u3002\u8fd9\u4e2a\u901a\u7528\u51fd\u6570\u5df2\u7ecf\u4e0d\u5c5e\u4e8e\u6211\u4eec\u672c\u6587\u6240\u8ff0\u7684VFS\u5c42\u7684\u5b9e\u73b0\u8303\u7574\u3002<\/p>\n
3.write\u51fd\u6570\u7684\u5b9e\u73b0<\/h3>\n
write\u7cfb\u7edf\u8c03\u7528\u5728VFS\u5c42\u7684\u5b9e\u73b0\u6d41\u7a0b\u4e0eread\u7c7b\u4f3c\uff0c\u53ea\u4e0d\u8fc7\u5728\u51fa\u73b0read\u7684\u5730\u65b9\u5c06\u5176\u76f8\u5e94\u7684\u7f6e\u6362\u4e3awrite\u3002<\/p>\n
\r\nSYSCALL_DEFINE3(write, unsigned int, fd, const char __user *, buf,\r\n size_t, count)\r\n{\r\n struct file *file;\r\n ssize_t ret = -EBADF;\r\n int fput_needed;\r\n\r\n file = fget_light(fd, &fput_needed);\r\n if (file) {\r\n loff_t pos = file_pos_read(file);\r\n ret = vfs_write(file, buf, count, &pos);\r\n file_pos_write(file, pos);\r\n fput_light(file, fput_needed);\r\n }\r\n\r\n return ret;\r\n}\r\n<\/pre>\n\u5f53\u7136\u6700\u7ec8\u5b9e\u73b0\u5199\u6587\u4ef6\u64cd\u4f5c\u7684\u51fd\u6570\u4e5f\u662ffile->f_op->write\u6216\u8005\u5185\u6838\u4e2d\u901a\u7528\u7684\u5199\u64cd\u4f5cgeneric_file_aio_write\u3002<\/p>\n
4.close()\u7684\u5b9e\u73b0<\/h3>\n
close\u7cfb\u7edf\u8c03\u7528\u5bf9\u5e94\u7684\u670d\u52a1\u4f8b\u7a0b\u4e2d\uff0c\u5b83\u9996\u5148\u901a\u8fc7fd\u5728\u6587\u4ef6\u5bf9\u8c61\u6570\u7ec4\u4e2d\u83b7\u53d6\u6587\u4ef6\u5bf9\u8c61\uff0c\u63a5\u7740\u5219\u5c06fd\u5904\u7684\u6587\u4ef6\u5bf9\u8c61\u6e05\u7a7a\u3002\u63a5\u4e0b\u6765\u7684\u5927\u90e8\u5206\u5de5\u4f5c\u90fd\u901a\u8fc7filp_close\u51fd\u6570\u5b8c\u6210\uff0c\u5b83\u4e3b\u8981\u7684\u5de5\u4f5c\u662f\u8c03\u7528flush\u94a9\u5b50\u51fd\u6570\u5c06\u9875\u9ad8\u901f\u7f13\u5b58\u4e2d\u7684\u6570\u636e\u5168\u90e8\u5199\u56de\u78c1\u76d8\uff0c\u91ca\u653e\u8be5\u6587\u4ef6\u4e0a\u7684\u6240\u6709\u9501\uff0c\u901a\u8fc7fput\u51fd\u6570\u91ca\u653e\u8be5\u6587\u4ef6\u5bf9\u8c61\u3002\u6700\u540e\u8fd4\u56de0\u6216\u8005\u4e00\u4e2a\u9519\u8bef\u7801\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
\u865a\u62df\u6587\u4ef6\u7cfb\u7edf\uff08Virtual Filesystem Switch\uff0cVFS\uff09\u4e3a\u5404\u79cd\u6587\u4ef6\u7cfb\u7edf\u63d0\u4f9b\u4e86\u4e00\u4e2a\u901a\u7528\u7684\u63a5\u53e3\uff0c […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[110,175],"tags":[174,404,179],"class_list":["post-4227","post","type-post","status-publish","format-standard","hentry","category-linux","category-175","tag-vfs","tag-404","tag-179"],"views":18292,"_links":{"self":[{"href":"http:\/\/edsionte.com\/techblog\/wp-json\/wp\/v2\/posts\/4227","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=4227"}],"version-history":[{"count":0,"href":"http:\/\/edsionte.com\/techblog\/wp-json\/wp\/v2\/posts\/4227\/revisions"}],"wp:attachment":[{"href":"http:\/\/edsionte.com\/techblog\/wp-json\/wp\/v2\/media?parent=4227"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/edsionte.com\/techblog\/wp-json\/wp\/v2\/categories?post=4227"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/edsionte.com\/techblog\/wp-json\/wp\/v2\/tags?post=4227"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}