[lxc-devel] hwaddr tuning in templates

[Serge Hallyn]

Quoting Guillaume ZITTA (lxc at zitta.fr):
> >>If not, my proposal:
> >> I set an incomplete (prefix) lxc.network.hwaddr in default conf.
> >> lxc-create complete it randomly and write it to the container's
> >>config.
> >>
> >>Does it make sense?
> >
> >I think so.  Just 'xx' in place of real numbers?
> >
> >>I do not/can't code in C, but perhaps I should try  ...
> >>
> >>Guillaume ZITTA
> 
> Please be kind, it's the second time I do "C" of my life :)
> 
> Note about randinit():
>  that kind of util can be used in network.c/lxc_mkifname() and
> lxccontainer.c/new_hwaddr()
> 
> It works for me, I did 1000 destroy/create (with fake template) in
> 43 sec without mac duplicate.
> 
> If I'm not completely doing wrong, I'll provide patch for manpage
> and HAVE_RAND_R ifdef.
> 
> please comment.

Looks good, except for one comment below, and if you do submit
this please do add a Signed-off-by line.

> 
> diff --git a/src/lxc/confile.c b/src/lxc/confile.c
> index c5ec4f3..5721e05 100644
> --- a/src/lxc/confile.c
> +++ b/src/lxc/confile.c
> @@ -509,6 +509,24 @@ static int macvlan_mode(int *valuep, const char
> *value)
>  	return -1;
>  }
> 
> +char *rand_complete_hwaddr(const char *hwaddr)
> +{
> +	const char hex[] = "0123456789abcdef";
> +	char *retval=NULL;
> +	retval = strdup(hwaddr);
> +	char *curs = retval;
> +
> +	randinit();
> +
> +	while (*curs != '\0')
> +	{
> +		if ( *curs == 'x' || *curs == 'X' )
> +			*curs = hex[rand() & 0x0F];
> +		curs++;
> +	}
> +	return retval;
> +}
> +
>  static int config_network_flags(const char *key, const char *value,
>  				struct lxc_conf *lxc_conf)
>  {
> @@ -576,11 +594,13 @@ static int config_network_hwaddr(const char
> *key, const char *value,
>  {
>  	struct lxc_netdev *netdev;
> 
> -	netdev = network_netdev(key, value, &lxc_conf->network);
> +	const char *newval = rand_complete_hwaddr(value);

newval got strdup()d above, but is never freed.  config_string_item()
will actually strdup that again for the value added to the
configuration.  So you need to free newval on exiting this function.

> +
> +	netdev = network_netdev(key, newval, &lxc_conf->network);
>  	if (!netdev)
>  		return -1;
> 
> -	return config_string_item(&netdev->hwaddr, value);
> +	return config_string_item(&netdev->hwaddr, newval);
>  }
> 
>  static int config_network_vlan_id(const char *key, const char *value,
> diff --git a/src/lxc/utils.c b/src/lxc/utils.c
> index 785f3e6..204179e 100644
> --- a/src/lxc/utils.c
> +++ b/src/lxc/utils.c
> @@ -1126,3 +1126,25 @@ void **lxc_append_null_to_array(void **array,
> size_t count)
>  	}
>  	return array;
>  }
> +
> +void randinit(void)
> +{
> +	/*
> +	srand pre-seed function based on /dev/urandom
> +	*/
> +	FILE *f;
> +	process_lock();
> +	f = fopen("/dev/urandom", "r");
> +	process_unlock();
> +	if (f) {
> +		unsigned int seed;
> +		int ret = fread(&seed, sizeof(seed), 1, f);
> +		if (ret != 1)
> +			seed = time(NULL);
> +		process_lock();
> +		fclose(f);
> +		process_unlock();
> +		srand(seed);
> +	} else
> +		srand(time(NULL));
> +}
> \ No newline at end of file
> diff --git a/src/lxc/utils.h b/src/lxc/utils.h
> index 945f1de..f20339b 100644
> --- a/src/lxc/utils.h
> +++ b/src/lxc/utils.h
> @@ -270,4 +270,7 @@ extern void **lxc_dup_array(void **array,
> lxc_dup_fn element_dup_fn, lxc_free_fn
>  extern void **lxc_append_null_to_array(void **array, size_t count);
> 
>  extern void dump_stacktrace(void);
> +
> +//initialize rand with urandom
> +extern void randinit(void);
>  #endif
> 
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