20 内核4.0.4文件打开异常

的确是有BUG，感觉是fopen和open不是共用同一个宏，导致传递参数的时候发生了错误。
这是我仿真调试的断点结果：

从fopen传递过来的flags显示的8进制值是0203001,0200000宏定义代表文件类型为目录，导致下面传递到文件系统的open接口时，解析错误。

在移植4.0.4的时候，有一个地方比较特别，dfs.h内的头文件fctnl.h，与sys/fctnl.h这个头文件定义的内容是不相同的，fctnl.h是RTT内核提供的头文件，sys/fctnl.h是gcc工具链提供的头文件，fopen产生的flags是符合sys/fctnl.h内的定义。

#ifndef    _SYS__DEFAULT_FCNTL_H_
#ifdef __cplusplus
extern "C" {
#endif
#define    _SYS__DEFAULT_FCNTL_H_
#include <_ansi.h>
#include <sys/cdefs.h>
#define    _FOPEN        (-1)    /* from sys/file.h, kernel use only */
#define    _FREAD        0x0001    /* read enabled */
#define    _FWRITE        0x0002    /* write enabled */
#define    _FAPPEND    0x0008    /* append (writes guaranteed at the end) */
#define    _FMARK        0x0010    /* internal; mark during gc() */
#define    _FDEFER        0x0020    /* internal; defer for next gc pass */
#define    _FASYNC        0x0040    /* signal pgrp when data ready */
#define    _FSHLOCK    0x0080    /* BSD flock() shared lock present */
#define    _FEXLOCK    0x0100    /* BSD flock() exclusive lock present */
#define    _FCREAT        0x0200    /* open with file create */
#define    _FTRUNC        0x0400    /* open with truncation */
#define    _FEXCL        0x0800    /* error on open if file exists */
#define    _FNBIO        0x1000    /* non blocking I/O (sys5 style) */
#define    _FSYNC        0x2000    /* do all writes synchronously */
#define    _FNONBLOCK    0x4000    /* non blocking I/O (POSIX style) */
#define    _FNDELAY    _FNONBLOCK    /* non blocking I/O (4.2 style) */
#define    _FNOCTTY    0x8000    /* don't assign a ctty on this open */

#define    O_ACCMODE    (O_RDONLY|O_WRONLY|O_RDWR)

/*
 * Flag values for open(2) and fcntl(2)
 * The kernel adds 1 to the open modes to turn it into some
 * combination of FREAD and FWRITE.
 */
#define    O_RDONLY    0        /* +1 == FREAD */
#define    O_WRONLY    1        /* +1 == FWRITE */
#define    O_RDWR        2        /* +1 == FREAD|FWRITE */
#define    O_APPEND    _FAPPEND
#define    O_CREAT        _FCREAT
#define    O_TRUNC        _FTRUNC
#define    O_EXCL        _FEXCL
#define O_SYNC        _FSYNC
/*    O_NDELAY    _FNDELAY     set in include/fcntl.h */
/*    O_NDELAY    _FNBIO         set in include/fcntl.h */
#define    O_NONBLOCK    _FNONBLOCK
#define    O_NOCTTY    _FNOCTTY
/* For machines which care - */
#if defined (__CYGWIN__)
#define _FBINARY        0x10000
#define _FTEXT          0x20000
#define _FNOINHERIT    0x40000
#define _FDIRECT        0x80000
#define _FNOFOLLOW      0x100000
#define _FDIRECTORY     0x200000
#define _FEXECSRCH      0x400000

#define O_BINARY    _FBINARY
#define O_TEXT        _FTEXT
#define O_CLOEXEC    _FNOINHERIT
#define O_DIRECT        _FDIRECT
#define O_NOFOLLOW      _FNOFOLLOW
#define O_DSYNC         _FSYNC
#define O_RSYNC         _FSYNC
#define O_DIRECTORY     _FDIRECTORY
#define O_EXEC          _FEXECSRCH
#define O_SEARCH        _FEXECSRCH
#endif

#define    _FREAD        0x0001    /* read enabled */
#define    _FCREAT        0x0200    /* open with file create */
#define    _FTRUNC        0x0400    /* open with truncation */
#define _FBINARY        0x10000

#define    O_WRONLY    1        /* +1 == FWRITE */
#define    O_CREAT        _FCREAT
#define    O_TRUNC        _FTRUNC
#define O_BINARY    _FBINARY

四个宏组合起来就是 0x10601 = 0203001 是符合上述的flags值
跟 FILE *fp = fopen(path, "wb"); 代码传递的参数吻合
应该是RTT内核的fctnl.h与编译器的sys/fctnl.h定义上有冲突，但是我编译的时候并没有提示redefined的警告，这个就很神奇了

总结的很到位。给你点个赞。不知道是否有解决方案，有的话欢迎PR，也欢迎讲你的理解提交到下面issue里面
https://github.com/RT-Thread/rt-thread/issues/5186