Re: Race condition with pasta COMMAND...

[Stefano Brivio <sbrivio@redhat.com>]

Hi Paul,

On Mon, 30 Jan 2023 19:08:14 +0100
Paul Holzinger <pholzing@redhat.com> wrote:

> Hi all,
> 
> while debugging some things I used `./pasta --config-net -- nslookup 
> google.com 1.1.1.1` to test dns.
> The problem is that does not work because the nslookup process will be 
> executed before pasta is
> ready with the netns setup, i.e. compare `./pasta --config-net -- ip a`.

Thanks for the report. I also hit this a couple of months ago but I
couldn't find yet the time to deal with it:

  https://bugs.passt.top/show_bug.cgi?id=37

> So a workaround is to spawn a shell and sleep: `sh -c "sleep 1; nslookup 
> google.com 1.1.1.1"`
> However this is ugly and does not ensure that the netns is ready after 
> one second. As a user
> I would expect pasta to wait until the setup is finished before it calls 
> exec().

Absolutely, yes.

As I mentioned on that ticket, I *think* that the only way to make sure
the setup is actually complete is to query back via netlink addresses
and routes we configured -- simply waiting until we successfully sent
netlink messages isn't enough, because it takes a (substantial) while
until addresses and routes are actually available.

> I can send a patch if you agree and I find some time.

That would be great, thanks in advance!

If you get to it, I think you could reuse nl_route() and nl_addr() from
netlink.c to perform the checks -- they might need to be extended a
bit, I'm not sure.

-- 
Stefano