tools: ynl-gen: support fixed headers in genetlink

Support genetlink families using simple fixed headers.
Assume fixed header is identical for all ops of the family for now.

Fixed headers are added to the request and reply structs as a _hdr
member, and copied to/from netlink messages appropriately.
Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://lore.kernel.org/r/20231213231432.2944749-4-kuba@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

tools/net/ynl/lib/ynl.c

@@ -191,12 +191,12 @@ ynl_ext_ack_check(struct ynl_sock *ys, const struct nlmsghdr *nlh,
 			     str ? " (" : "");
 
 		start = mnl_nlmsg_get_payload_offset(ys->nlh,
-						     sizeof(struct genlmsghdr));
+						     ys->family->hdr_len);
 		end = mnl_nlmsg_get_payload_tail(ys->nlh);
 
 		off = ys->err.attr_offs;
 		off -= sizeof(struct nlmsghdr);
-		off -= sizeof(struct genlmsghdr);
+		off -= ys->family->hdr_len;
 
 		n += ynl_err_walk(ys, start, end, off, ys->req_policy,
 				  &bad_attr[n], sizeof(bad_attr) - n, NULL);
@@ -217,14 +217,14 @@ ynl_ext_ack_check(struct ynl_sock *ys, const struct nlmsghdr *nlh,
 			     bad_attr[0] ? ", " : (str ? " (" : ""));
 
 		start = mnl_nlmsg_get_payload_offset(ys->nlh,
-						     sizeof(struct genlmsghdr));
+						     ys->family->hdr_len);
 		end = mnl_nlmsg_get_payload_tail(ys->nlh);
 
 		nest_pol = ys->req_policy;
 		if (tb[NLMSGERR_ATTR_MISS_NEST]) {
 			off = mnl_attr_get_u32(tb[NLMSGERR_ATTR_MISS_NEST]);
 			off -= sizeof(struct nlmsghdr);
-			off -= sizeof(struct genlmsghdr);
+			off -= ys->family->hdr_len;
 
 			n += ynl_err_walk(ys, start, end, off, ys->req_policy,
 					  &miss_attr[n], sizeof(miss_attr) - n,

tools/net/ynl/lib/ynl.h

@@ -44,6 +44,7 @@ struct ynl_error {
 struct ynl_family {
 /* private: */
 	const char *name;
+	size_t hdr_len;
 	const struct ynl_ntf_info *ntf_info;
 	unsigned int ntf_info_size;
 };

tools/net/ynl/ynl-gen-c.py

@@ -1124,6 +1124,10 @@ class RenderInfo:
         self.op_mode = op_mode
         self.op = op
 
+        self.fixed_hdr = None
+        if op and op.fixed_header:
+            self.fixed_hdr = 'struct ' + c_lower(op.fixed_header)
+
         # 'do' and 'dump' response parsing is identical
         self.type_consistent = True
         if op_mode != 'do' and 'dump' in op:
@@ -1570,7 +1574,9 @@ def _multi_parse(ri, struct, init_lines, local_vars):
     if struct.nested:
         iter_line = "mnl_attr_for_each_nested(attr, nested)"
     else:
-        iter_line = "mnl_attr_for_each(attr, nlh, sizeof(struct genlmsghdr))"
+        if ri.fixed_hdr:
+            local_vars += ['void *hdr;']
+        iter_line = "mnl_attr_for_each(attr, nlh, yarg->ys->family->hdr_len)"
 
     array_nests = set()
     multi_attrs = set()
@@ -1603,6 +1609,9 @@ def _multi_parse(ri, struct, init_lines, local_vars):
     for arg in struct.inherited:
         ri.cw.p(f'dst->{arg} = {arg};')
 
+    if ri.fixed_hdr:
+        ri.cw.p('hdr = mnl_nlmsg_get_payload_offset(nlh, sizeof(struct genlmsghdr));')
+        ri.cw.p(f"memcpy(&dst->_hdr, hdr, sizeof({ri.fixed_hdr}));")
     for anest in sorted(all_multi):
         aspec = struct[anest]
         ri.cw.p(f"if (dst->{aspec.c_name})")
@@ -1723,6 +1732,10 @@ def print_req(ri):
         ret_err = 'NULL'
         local_vars += [f'{type_name(ri, rdir(direction))} *rsp;']
 
+    if ri.fixed_hdr:
+        local_vars += ['size_t hdr_len;',
+                       'void *hdr;']
+
     print_prototype(ri, direction, terminate=False)
     ri.cw.block_start()
     ri.cw.write_func_lvar(local_vars)
@@ -1733,6 +1746,13 @@ def print_req(ri):
     if 'reply' in ri.op[ri.op_mode]:
         ri.cw.p(f"yrs.yarg.rsp_policy = &{ri.struct['reply'].render_name}_nest;")
     ri.cw.nl()
+
+    if ri.fixed_hdr:
+        ri.cw.p("hdr_len = sizeof(req->_hdr);")
+        ri.cw.p("hdr = mnl_nlmsg_put_extra_header(nlh, hdr_len);")
+        ri.cw.p("memcpy(hdr, &req->_hdr, hdr_len);")
+        ri.cw.nl()
+
     for _, attr in ri.struct["request"].member_list():
         attr.attr_put(ri, "req")
     ri.cw.nl()
@@ -1773,9 +1793,11 @@ def print_dump(ri):
                   'struct nlmsghdr *nlh;',
                   'int err;']
 
-    for var in local_vars:
-        ri.cw.p(f'{var}')
-    ri.cw.nl()
+    if ri.fixed_hdr:
+        local_vars += ['size_t hdr_len;',
+                       'void *hdr;']
+
+    ri.cw.write_func_lvar(local_vars)
 
     ri.cw.p('yds.ys = ys;')
     ri.cw.p(f"yds.alloc_sz = sizeof({type_name(ri, rdir(direction))});")
@@ -1788,6 +1810,12 @@ def print_dump(ri):
     ri.cw.nl()
     ri.cw.p(f"nlh = ynl_gemsg_start_dump(ys, {ri.nl.get_family_id()}, {ri.op.enum_name}, 1);")
 
+    if ri.fixed_hdr:
+        ri.cw.p("hdr_len = sizeof(req->_hdr);")
+        ri.cw.p("hdr = mnl_nlmsg_put_extra_header(nlh, hdr_len);")
+        ri.cw.p("memcpy(hdr, &req->_hdr, hdr_len);")
+        ri.cw.nl()
+
     if "request" in ri.op[ri.op_mode]:
         ri.cw.p(f"ys->req_policy = &{ri.struct['request'].render_name}_nest;")
         ri.cw.nl()
@@ -1845,6 +1873,10 @@ def _print_type(ri, direction, struct):
 
     ri.cw.block_start(line=f"struct {ri.family.c_name}{suffix}")
 
+    if ri.fixed_hdr:
+        ri.cw.p(ri.fixed_hdr + ' _hdr;')
+        ri.cw.nl()
+
     meta_started = False
     for _, attr in struct.member_list():
         for type_filter in ['len', 'bit']:
@@ -2482,6 +2514,10 @@ def render_user_family(family, cw, prototype):
 
     cw.block_start(f'{symbol} = ')
     cw.p(f'.name\t\t= "{family.c_name}",')
+    if family.fixed_header:
+        cw.p(f'.hdr_len\t= sizeof(struct genlmsghdr) + sizeof(struct {c_lower(family.fixed_header)}),')
+    else:
+        cw.p('.hdr_len\t= sizeof(struct genlmsghdr),')
     if family.ntfs:
         cw.p(f".ntf_info\t= {family['name']}_ntf_info,")
         cw.p(f".ntf_info_size\t= MNL_ARRAY_SIZE({family['name']}_ntf_info),")