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diff --git a/lib9p/protogen/c9util.py b/lib9p/protogen/c9util.py
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+# lib9p/protogen/c9util.py - Utilities for generating lib9p-specific C
+#
+# Copyright (C) 2024-2025  Luke T. Shumaker <lukeshu@lukeshu.com>
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+import typing
+
+import idl
+
+# This strives to be "general-purpose" in that it just acts on the
+# *.9p inputs; but (unfortunately?) there are a few special-cases in
+# this script, marked with "SPECIAL".
+
+# pylint: disable=unused-variable
+__all__ = [
+    "add_prefix",
+    "ident",
+    "Ident",
+    "IDENT",
+    "ver_enum",
+    "ver_ifdef",
+    "ver_cond",
+    "typename",
+    "idl_expr",
+]
+
+# idents #######################################################################
+
+
+def add_prefix(p: str, s: str) -> str:
+    if s.startswith("_"):
+        return "_" + p + s[1:]
+    return p + s
+
+
+def _ident(p: str, s: str) -> str:
+    return add_prefix(p, s.replace(".", "_"))
+
+
+def ident(s: str) -> str:
+    return _ident("lib9p_", s)
+
+
+def Ident(s: str) -> str:
+    return _ident("lib9p_".upper(), s)
+
+
+def IDENT(s: str) -> str:
+    return _ident("lib9p_", s).upper()
+
+
+# versions #####################################################################
+
+
+def ver_enum(ver: str) -> str:
+    return Ident("VER_" + ver)
+
+
+def ver_ifdef(versions: typing.Collection[str]) -> str:
+    return " || ".join(
+        f"CONFIG_9P_ENABLE_{v.replace('.', '_')}" for v in sorted(versions)
+    )
+
+
+def ver_cond(versions: typing.Collection[str]) -> str:
+    if len(versions) == 1:
+        v = next(v for v in versions)
+        return f"is_ver(ctx, {v.replace('.', '_')})"
+    return "( " + (" || ".join(ver_cond({v}) for v in sorted(versions))) + " )"
+
+
+# misc #########################################################################
+
+
+def typename(typ: idl.Type, parent: idl.StructMember | None = None) -> str:
+    match typ:
+        case idl.Primitive():
+            if typ.value == 1 and parent and parent.cnt:  # SPECIAL (string)
+                return "[[gnu::nonstring]] char"
+            return f"uint{typ.value*8}_t"
+        case idl.Number():
+            return ident(f"{typ.typname}_t")
+        case idl.Bitfield():
+            return ident(f"{typ.typname}_t")
+        case idl.Message():
+            return f"struct {ident(f'msg_{typ.typname}')}"
+        case idl.Struct():
+            return f"struct {ident(typ.typname)}"
+        case _:
+            raise ValueError(f"not a type: {typ.__class__.__name__}")
+
+
+def idl_expr(expr: idl.Expr, lookup_sym: typing.Callable[[str], str]) -> str:
+    ret: list[str] = []
+    for tok in expr.tokens:
+        match tok:
+            case idl.ExprOp():
+                ret.append(tok.op)
+            case idl.ExprLit():
+                ret.append(str(tok.val))
+            case idl.ExprSym(symname="s32_max"):
+                ret.append("INT32_MAX")
+            case idl.ExprSym(symname="s64_max"):
+                ret.append("INT64_MAX")
+            case idl.ExprSym():
+                ret.append(lookup_sym(tok.symname))
+            case _:
+                assert False
+    return " ".join(ret)