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Message-ID: <7ddb3b35-58fe-a376-f839-d9fc6de9ffc5@redhat.com>
Date: Wed, 2 Aug 2023 11:51:02 +0200
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Subject: Re: [PATCH] tap: include errno in error when tap_ns_tun() fails
To: David Gibson <david@gibson.dropbear.id.au>
References: <20230801115016.37118-2-pholzing@redhat.com>
<ZMmzxSUUWh2vOZEV@zatzit>
From: Paul Holzinger <pholzing@redhat.com>
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On 02/08/2023 03:39, David Gibson wrote:
> 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.
Thanks, I only did a quick test with chmod 600 /dev/net/tun and got the
expected EACCES so I assumed it worked fine but anyway your series looks
much better.
>
>
>>
>> pasta_ns_conf(c);
>>