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Re: [libvirt] PATCH: 3/5: Introduce a container controller process



DB> +/**
DB> + * lxcControllerMoveInterfaces
DB> + * @nveths: number of interfaces
DB> + * @veths: interface names
DB> + * @container: pid of container
DB> + *
DB> + * Moves network interfaces into a container's namespace
DB> + *
DB> + * Returns 0 on success or -1 in case of error
DB> + */
DB> +static int lxcControllerMoveInterfaces(int nveths,
DB> +                                       char **veths,
DB> +                                       pid_t container)
DB> +{
DB> +    int i;
DB> +    for (i = 0 ; i < nveths ; i++)
DB> +        if (moveInterfaceToNetNs(veths[i], container) < 0) {
DB> +            lxcError(NULL, NULL, VIR_ERR_INTERNAL_ERROR,
DB> +                     _("failed to move interface %s to ns %d"),
DB> +                     veths[i], container);
DB> +            return -1;
DB> +        }
DB> +
DB> +    return 0;
DB> +}

I'm not sure why, but the call to this function causes a failure on my
system.  I think that it's related to luck somehow, so I don't think
it's something that was really introduced by this set, but it prevents
me from starting a container with a network interface.

I've tracked it down to the actual virRun() of the 'ip' command.  If I
comment out the line that virRun()'s ip, everything works fine.
However, if it actually gets run, the container never receives the
continue message.

I added a loop in lxcWaitForContinue() that reads the socket
character-by-character instead of bailing out if the first character
isn't 'c'.  The result was a bunch of control characters followed by
'c'.

Based on these two facts, I would tend to guess that somehow the exec
of ip is causing some terminal stuff (yes, that's my technical term
for it) to be written to the socket ahead of the continue message.  I
changed 'ip' to 'true' in moveInterfaceToNetNs() and it behaves the
same (which absolves ip itself).  I removed the virRun() and replaced
with a fork()..exec() and it behaves the same.  I set FD_CLOEXEC on
the socket pair, and it behaves the same.

I have no idea (or rather, I'm out of ideas) why this is happening.  I
assume you're not seeing it because you're not playing with
network-enabled guests.

DB> +int lxcControllerStart(lxc_vm_def_t *def,
DB> +                       int nveths,
DB> +                       char **veths,
DB> +                       int monitor,
DB> +                       int appPty,
DB> +                       const char *logfile)
DB> +{

<snip>

DB> +    if ((logfd = open(logfile, O_WRONLY | O_TRUNC)) < 0)

You need O_CREAT here.

DB> @@ -590,82 +578,75 @@

<snip>

DB> -    if (0 != (rc = lxcSetupInterfaces(conn, vm))) {

You changed the condition from "nonzero" here...

<snip>

DB> +    if (lxcSetupInterfaces(conn, vm->def, &nveths, &veths) < 0)

...to "negative" here, which makes the start process not notice some
of the failure paths in that function, and thus will erroneously
return success.

In general, I think this is an excellent approach, but I don't really
like how many (dozens of) failure points there are in the controller
and container setup procedure that result in a silent failure.  Almost
all of them leave libvirtd thinking that the container/controller is
running, but in fact, it _exit(1)'d long ago.

-- 
Dan Smith
IBM Linux Technology Center
Open Hypervisor Team
email: danms us ibm com

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