linux-kernel - Re: [PATCH bpf-next v3 6/6] selftests/bpf: fix file descriptor assertion in open

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Message-ID: <67be0af39dbf7_25ccfc2943c@willemb.c.googlers.com.notmuch>
Date: Tue, 25 Feb 2025 13:24:51 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Marcus Wichelmann <marcus.wichelmann@...zner-cloud.de>, 
 netdev@...r.kernel.org, 
 linux-kernel@...r.kernel.org, 
 bpf@...r.kernel.org, 
 linux-kselftest@...r.kernel.org
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 jasowang@...hat.com, 
 andrew+netdev@...n.ch, 
 davem@...emloft.net, 
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 daniel@...earbox.net, 
 martin.lau@...ux.dev, 
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 marcus.wichelmann@...zner-cloud.de
Subject: Re: [PATCH bpf-next v3 6/6] selftests/bpf: fix file descriptor
 assertion in open_tuntap helper

Marcus Wichelmann wrote:
> The open_tuntap helper function uses open() to get a file descriptor for
> /dev/net/tun.
> 
> The open(2) manpage writes this about its return value:
> 
>   On success, open(), openat(), and creat() return the new file
>   descriptor (a nonnegative integer).  On error, -1 is returned and
>   errno is set to indicate the error.
> 
> This means that the fd > 0 assertion in the open_tuntap helper is
> incorrect and should rather check for fd >= 0.
> 
> When running the BPF selftests locally, this incorrect assertion was not
> an issue, but the BPF kernel-patches CI failed because of this:
> 
>   open_tuntap:FAIL:open(/dev/net/tun) unexpected open(/dev/net/tun):
>   actual 0 <= expected 0
> 
> Signed-off-by: Marcus Wichelmann <marcus.wichelmann@...zner-cloud.de>

Reviewed-by: Willem de Bruijn <willemb@...gle.com>