[bug report] opendir(3): document file offset behavior for fdopendir()

[bug report] opendir(3): document file offset behavior for fdopendir()

[Jorge Almeida]

Hi,

The opendir(3) manual page currently describes fdopendir() as being
"like opendir(), but returns a directory stream for the directory
referred to by the open file descriptor fd."

However, it omits a critical detail documented in POSIX (fdopendir(3p))
and the BSD man pages: fdopendir() uses the current file offset of fd
rather than resetting it to zero.

If a caller duplicates an open directory descriptor with dup() and
exhausts the stream with readdir(), subsequent dup() + fdopendir()
calls will immediately hit EOF unless rewinddir() or lseek() is called.
By contrast, fdopen(3) explicitly warns that the stream's file
position indicator is set to that belonging to fd.

Could a similar note be added to the fdopendir() description in
opendir(3)?

Thanks.

Re: [bug report] opendir(3): document file offset behavior for fdopendir()

[Alejandro Colomar]

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Hi Jorge,

> Date: 2026-11-13 21:28:32+0000
> From: Jorge Almeida <jjalmeida@gmail.com>
>
> Hi,
> 
> The opendir(3) manual page currently describes fdopendir() as being
> "like opendir(), but returns a directory stream for the directory
> referred to by the open file descriptor fd."
> 
> However, it omits a critical detail documented in POSIX (fdopendir(3p))
> and the BSD man pages: fdopendir() uses the current file offset of fd
> rather than resetting it to zero.
> 
> If a caller duplicates an open directory descriptor with dup() and
> exhausts the stream with readdir(), subsequent dup() + fdopendir()
> calls will immediately hit EOF unless rewinddir() or lseek() is called.
> By contrast, fdopen(3) explicitly warns that the stream's file
> position indicator is set to that belonging to fd.
> 
> Could a similar note be added to the fdopendir() description in
> opendir(3)?

Would you mind sending a patch?

If so, you can have a look at
<https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING>
and
<https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING.d/>
for some help (and I will gladly help if you have any questions).


Have a lovely night!
Alex

> 
> Thanks.
> 

-- 
<https://www.alejandro-colomar.es>

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