Re: errno from open(<directory>) ?

[Tim Rühsen]

On 05/22/2017 10:38 PM, Bruno Haible wrote:
> Tim Rühsen wrote:
>>>> on GNU/Linux open() on a directory returns -1 and sets errno to EISDIR.
>>>
>>> No, for example on my platform (Fedora 25 x86-64), 'strace cat .'
>>> outputs the line 'open(".", O_RDONLY) = 3'.
>>
>> Same here on Debian unstable.
>> What you want to say is, that it depends on the flags.
>> And you are right, I wasn't very precise in that point.
>>
>> Here we use
>> fd = open(fname, O_WRONLY | flag | O_CREAT | O_NONBLOCK | O_BINARY, S_IRUSR 
>> | 
>> S_IWUSR | S_IRGRP | S_IROTH);
>>
>> 'flag' might be one of O_TRUNC, O_APPEND or O_EXCL.
>>
>> A test with different flags for open(<existing directory>) shows failure + 
>> errno EISDIR when opening for writing.
> 
> This portability issue is an ideal "skills ramp up" for someone who has only 
> done
> smaller contributions to gnulib so far.
> 
> Steps:
> 1) Consider the standards: What does POSIX:2008 say about the issue?
> 2) Extend the unit test of module 'open'.
> 3) Ask us to test these extended unit tests on various platforms (Mac OS X, 
> Solaris,
>    FreeBSD, HP-UX, etc.).
> 4) Mention the issue in the doc section about 'open'.
> 5) Extend the Autoconf test to recognize this case and arrange to override the
>    'open' function when the Autoconf test fails.
> 6) Extend the workaround (lib/open.c) and make sure the unit test now succeeds
>    on the relevant platform(s).
> 
> Any takers? Tim? Gisle?

Basically a very good idea. But I am really busy working on
wget2/libwget, maintaining projects and mentoring GSOC students.

I just created a Wiki[1] page describing this issue. Maybe we can get
one (or more) of our students to work on this - it is still 'community
bonding' time.

Thanks for providing the detailed steps.

> 
> Bruno

[1]
https://gitlab.com/gnuwget/wget2/wikis/enhancing-gnulib-module-'open'-to-return-eisdir-regarding-posix.2008

With Best Regards, Tim

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