open(名称，O_CREAT | O_DIRECTORY，模式)的预期行为是什么? [英] What's the expected behavior of open(name, O_CREAT|O_DIRECTORY, mode)?

问题描述

尽管仔细阅读了相关的标准文档，但我可以当用包含O_CREAT|O_DIRECTORY的标志调用open系统调用时，不了解在POSIX兼容系统中预期的行为是什么.

Despite a careful read of the related standard documentation, I can't understand what's the expected behavior in POSIX compliant systems when a open system call is invoked with flags including O_CREAT|O_DIRECTORY.

标准规定

如果将O_CREAT和O_DIRECTORY设置为，并且，所请求的访问模式既不是O_WRONLY也不是O_RDWR，则结果不确定.

If O_CREAT and O_DIRECTORY are set and the requested access mode is neither O_WRONLY nor O_RDWR, the result is unspecified.

但是，它既没有指定(O_CREAT|O_DIRECTORY|O_WRONLY)也没有指定(O_CREAT|O_DIRECTORY|O_RDWR)的系统行为.实际上，据我所知，EISDIR上的行为仅适用于现有目录.

However it does not specify the behavior of the system with neither (O_CREAT|O_DIRECTORY|O_WRONLY) nor (O_CREAT|O_DIRECTORY|O_RDWR). Indeed (as far as I can understand) the behavior on EISDIR only apply to existing directories.

在与O_CREATE有关的部分中，标准指定了当命名文件不存在时，

In the section related to O_CREATE, the standard specifies that, when the named file does not exist,

如果未设置O_DIRECTORY ，则应将文件创建为常规文件； [...]

if O_DIRECTORY is not set the file shall be created as a regular file; [...]

但是同样，它也没有指定如果设置O_DIRECTORY也会发生什么.

but again it does not specify what will happen if O_DIRECTORY is set too.

我查看了 NetBSD的手册页(众所周知，它非常在乎POSIX的合规性)和 Linux (这是广泛使用的系统，尽管实际上不是POSIX)，但我找不到任何澄清.

I've looked the manual pages of both NetBSD (which notoriously cares a lot about POSIX compliance) and Linux (which is a widely used system, despite not actually a POSIX one) but I can't find any clarification.

说未指定两个标志的使用是否正确? 如果是这样，最常见的行为是什么?

Is it correct to say that the use of both flags is unspecified? And if so, what's the most common behavior?

在任何符合POSIX的操作系统上，open(name, O_CREAT|O_DIRECTORY, mode)是否等同于mkdir?

Is open(name, O_CREAT|O_DIRECTORY, mode) equivalent to mkdir on any POSIX compliant OS?

推荐答案

netbsd本身在vn_open中包含以下内容:

netbsd itself contains the following in vn_open:

if ((fmode & (O_CREAT | O_DIRECTORY)) == (O_CREAT | O_DIRECTORY))
        return EINVAL;

因此与这2个的任何组合都会被直接拒绝.

so any combination with these 2 is straight up rejected.

在Linux中，它有点毛茸茸，但是任何琐碎的测试都会告诉您目录也没有创建，但是您最终可以得到一个文件

in linux it's a little bit more hairy, but any trivial test will show you that the directory is not created either, but you can end up with a file

对于踢球，我还检查了freebsd，它从未以O_DIRECTORY开头创建任何东西

for kicks i also checked freebsd, which never ends up creating anything with O_DIRECTORY in the first place

如果您正在寻找的是可以将fd退还给您的mkdir，恐怕没有任何东西了.另一方面，您应该可以使用O_DIRECTORY安全地打开任何您已创建的内容.

if what you are looking for is a mkdir which gives you back the fd, i'm afraid there is nothing of the sort. on the other hand you should be able to safely open with O_DIRECTORY anything you mkdir'ed.

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