netdev - Re: [PATCH net-next v1 1/2] tools: ynl: add user-header and struct attr support

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Date:   Sat, 18 Mar 2023 16:46:50 +0000
From:   Donald Hunter <donald.hunter@...hat.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Donald Hunter <donald.hunter@...il.com>, netdev@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next v1 1/2] tools: ynl: add user-header and struct
 attr support

On Sat, 18 Mar 2023 at 04:50, Jakub Kicinski <kuba@...nel.org> wrote:
>
> On Thu, 16 Mar 2023 12:01:41 +0000 Donald Hunter wrote:
> > Subject: [PATCH net-next v1 1/2] tools: ynl: add user-header and struct attr support
>
> The use of "and" usually indicates it should be 2 separate patches ;)

Ack. I'll try and split it into two.

> > +  user-header:
> > +    description: Name of the struct definition for the user header for the family.
> > +    type: string
>
> Took me a minute to remember this is header as in protocol header
> not header as in C header file :) Would it possibly be better to call it
> fixed-header ? Can't really decide myself.

I went with user header because the generic netlink howto calls it the
"optional user specific message header" but happy to go with fixed-header.

> But the description definitely need to be more verbose:
>
> description: |
>   Name of the structure defining the fixed-length protocol header.
>   This header is placed in a message after the netlink and genetlink
>   headers and before any attributes.

Agreed, this is a much clearer description.

> > +    def as_array(self, type):
> > +        format, _ = self.type_formats[type]
> > +        return list({ x[0] for x in struct.iter_unpack(format, self.raw) })
>
> The Python is strong within you :)
>
> > +    def as_struct(self, members):
> > +        value = dict()
> > +        offset = 0
> > +        for m in members:
> > +            type = m['type']
>
> Accessing the spec components directly is a bit of an anti-pattern,
> can we parse the struct description into Python objects in
> tools/net/ynl/lib/nlspec.py ?

Ack, will do.

> > +            format, size = self.type_formats[type]
> > +            decoded = struct.unpack_from(format, self.raw, offset)
> > +            offset += size
> > +            value[m['name']] = decoded[0]
> > +        return value
> > +
> >      def __repr__(self):
> >          return f"[type:{self.type} len:{self._len}] {self.raw}"
> >
> > @@ -200,7 +220,7 @@ def _genl_msg(nl_type, nl_flags, genl_cmd, genl_version, seq=None):
> >      if seq is None:
> >          seq = random.randint(1, 1024)
> >      nlmsg = struct.pack("HHII", nl_type, nl_flags, seq, 0)
> > -    genlmsg = struct.pack("bbH", genl_cmd, genl_version, 0)
> > +    genlmsg = struct.pack("BBH", genl_cmd, genl_version, 0)
>
> Should also be a separate patch

Yep, I will separate this into its own patch.

> >      return nlmsg + genlmsg
> >
> >
> > @@ -258,14 +278,22 @@ def _genl_load_families():
> >
> >
> >  class GenlMsg:
> > -    def __init__(self, nl_msg):
> > +    def __init__(self, nl_msg, extra_headers = []):
> >          self.nl = nl_msg
> >
> >          self.hdr = nl_msg.raw[0:4]
> > -        self.raw = nl_msg.raw[4:]
> > +        offset = 4
> >
> > -        self.genl_cmd, self.genl_version, _ = struct.unpack("bbH", self.hdr)
> > +        self.genl_cmd, self.genl_version, _ = struct.unpack("BBH", self.hdr)
> >
> > +        self.user_attrs = dict()
> > +        for m in extra_headers:
> > +            format, size = NlAttr.type_formats[m['type']]
> > +            decoded = struct.unpack_from(format, nl_msg.raw, offset)
> > +            offset += size
> > +            self.user_attrs[m['name']] = decoded[0]
>
> user_attrs?

Um, attrs of the user-header. I'll try to name this better.

> > +        self.raw = nl_msg.raw[offset:]
> >          self.raw_attrs = NlAttrs(self.raw)
> >
> >      def __repr__(self):
> > @@ -315,6 +343,7 @@ class YnlFamily(SpecFamily):
> >              setattr(self, op.ident_name, bound_f)
> >
> >          self.family = GenlFamily(self.yaml['name'])
> > +        self._user_header = self.yaml.get('user-header', None)
> >
> >      def ntf_subscribe(self, mcast_name):
> >          if mcast_name not in self.family.genl_family['mcast']:
> > @@ -358,7 +387,7 @@ class YnlFamily(SpecFamily):
> >                  raw >>= 1
> >                  i += 1
> >          else:
> > -            value = enum['entries'][raw - i]
> > +            value = enum.entries_by_val[raw - i]['name']
>
> Also a separate fix :S

Ack, will do.