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Date: Mon, 01 Mar 2021 16:58:07 +0100
From: Florian Weimer <>
To: enh <>
Cc:,  Rich Felker <>
Subject: Re: Lifetime of object returned by readdir

> On Tue, Feb 23, 2021 at 10:32 AM Florian Weimer <> wrote:
>  > 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).
> i suspect anyone iterating over a directory that large has other
> problems :-)

As has already been said, it's not necessarily a matter of directory

> fwiw, the only calls to telldir() or seekdir() in Android (not
> counting any vendor blobs i can't see the source to) are in the bionic
> unit tests and other languages' runtime wrappers (rust/python).

There are some thorny issues about read position invalidation and file
deletion.  It's strange we don't see more issues around that.  I would
expect that a readdir/unlink loop would fail to empty a directory in at
least some cases.  Maybe bulk deletion tools retry at a higher level if
they encounter an rmdir ENOTEMPTY failure.


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