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Date: Tue, 23 Feb 2021 19:30:52 +0100
From: Florian Weimer <>
To: enh <>
Cc:,  Rich Felker <>
Subject: Re: Lifetime of object returned by readdir

> POSIX already explicitly says that seekdir() affects the _next_
> readdir().

That's because it's the only way its effect is observable.

The glibc implementation of seekdir performs an immediate seek, but if
the seek fails, that error is not really observable (except for reading
the implementation and inferring that the errno = 0 hack will work).  I
had not realized that seekdir returns void.  Maybe that argues in favor
of a delayed seek upon the next readdir call.

> does anyone have an implementation where rewinddir()/seekdir()
> actually invalidate the previous readdir()? seems unlikely?

Probably not.  But there's also the issue of fitting the directory
offset (usually off64_t, maybe even something larger) into the long int
return value of telldir, so there could be quite a bit of magic going on
in the background (considering that telldir cannot indicate failure).


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