Re: [B.A.T.M.A.N.] [PATCHv2] batctl: Use netlink to replace some of debugfs

Andrew Lunn
2016-05-03T13:08:57Z

On Tue, May 03, 2016 at 02:54:26PM +0200, Sven Eckelmann wrote:
> On Tuesday 03 May 2016 14:47:19 Andrew Lunn wrote:
> > On Tue, May 03, 2016 at 02:26:34PM +0200, Sven Eckelmann wrote:
> > > On Tuesday 03 May 2016 14:20:46 Andrew Lunn wrote:
> > > [...]
> > > > There does not seem to be a way to say that BATADV_ATTR_VERSION is
> > > > also an NLA_STRING.
> > >
> > > Please check "policy" in the link I gave you.
> >
> > I did. And i still don't get how you can check the type.
> >
> > Andrew
>
> struct nla_policy {
> uint16_t type;
> uint16_t minlen;
> uint16_t maxlen;
> };
>
> there is an entry for type, minlen and maxlen. The type member is to check for
> the type. Here is an example how to check the type from batctl:
>
> static struct nla_policy info_data_link_policy[IFLA_MAX + 1] = {
> [IFLA_LINKINFO] = { .type = NLA_NESTED },
> [IFLA_LINK] = { .type = NLA_U32 },
> };
> [...]
> ret = nlmsg_parse(n, sizeof(struct ifinfomsg), tb, IFLA_MAX,
> info_data_link_policy);

Ah. Now i get it.

The problem is the overloaded 'type'. An attribute in a message has a
header which includes a type. It takes the value
e.g. BATADV_ATTR_VERSION. In nla_policy, we again have type, but this
time it takes e.g. NLA_U32.

Once you figure out type != type, it all becomes clear...

Andrew