Re: [PATCH] tap: include errno in error when tap_ns_tun() fails

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Aug 01, 2023 at 01:50:17PM +0200, Paul Holzinger wrote:
> It is important to know why a syscall failed so pasta should include the
> errno in the error message. This is still not perfect as we do not know
> which of functions (open, ioctl, if_nametoindex) failed but it should at
> least include more important context.

Uh.. we certainly want this, but I don't think this implementation
will quite do it.

> 
> This change was inspiered by a podman issue[1].
> 
> [1] https://github.com/containers/podman/issues/19428
> 
> Signed-off-by: Paul Holzinger <pholzing@redhat.com>
> ---
>  tap.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/tap.c b/tap.c
> index a6a73d3..c212616 100644
> --- a/tap.c
> +++ b/tap.c
> @@ -1205,7 +1205,8 @@ static void tap_sock_tun_init(struct ctx *c)
>  
>  	NS_CALL(tap_ns_tun, c);

NS_CALL means we're running the function in an ephemeral
thread/process/thingy..

>  	if (tun_ns_fd == -1)
> -		die("Failed to open tun socket in namespace");
> +		die("Failed to open tun socket in namespace: %s",
> +		    strerror(errno));

..which means we can't rely on it actually setting errno in the
original process.  The ephemeral thread does share memory, but modern
errno is a weird per-thread thingy, so I'm not entirely sure what will
happen here, but I'm certainly not confident about it working as we'd
like.

I'll have a crack at a more robust approach today.


>  
>  	pasta_ns_conf(c);
>  

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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