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Message-ID: <87czwieui8.fsf@oldenburg.str.redhat.com>
Date: Mon, 01 Mar 2021 16:58:07 +0100
From: Florian Weimer <fweimer@...hat.com>
To: enh <enh@...gle.com>
Cc: libc-coord@...ts.openwall.com, Rich Felker <dalias@...c.org>
Subject: Re: Lifetime of object returned by readdir
> On Tue, Feb 23, 2021 at 10:32 AM Florian Weimer <fweimer@...hat.com> 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
size.
> 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.
Thanks,
Florian
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