lib/qobj.h

   1 // SPDX-License-Identifier: ISC
   2 /*
   3  * Copyright (c) 2015-16  David Lamparter, for NetDEF, Inc.
   4  */
   5
   6 #ifndef _QOBJ_H
   7 #define _QOBJ_H
   8
   9 #include <stdint.h>
  10 #include <stdlib.h>
  11 #include <stddef.h>
  12
  13 #include "typesafe.h"
  14
  15 #ifdef __cplusplus
  16 extern "C" {
  17 #endif
  18
  19 /* reserve a specific amount of bytes for a struct, which can grow up to
  20  * that size (or be dummy'd out if not needed)
  21  *
  22  * note the padding's array size will be an error if it gets negative or zero;
  23  * this is intentional to prevent the struct from growing beyond the allocated
  24  * space.
  25  */
  26 #ifndef __cplusplus
  27 #define RESERVED_SPACE_STRUCT(name, fieldname, size)                           \
  28         struct {                                                               \
  29                 struct name fieldname;                                         \
  30                 char padding##fieldname[size - sizeof(struct name)];           \
  31         };
  32 #else
  33 #define RESERVED_SPACE_STRUCT(name, fieldname, size)                           \
  34         struct name fieldname;                                                 \
  35         char padding##fieldname[size - sizeof(struct name)];
  36 #endif
  37
  38 /* don't need struct definitions for these here.  code actually using
  39  * these needs to define the struct *before* including this header.
  40  * HAVE_QOBJ_xxx should be defined to +1 in that case, like this:
  41  *
  42  * #if defined(HAVE_QOBJ_NODETYPE_CLI) && HAVE_QOBJ_NODETYPE_CLI < 0
  43  * #error include files are in wrong order
  44  * #else
  45  * #define HAVE_QOBJ_NODETYPE_CLI 1
  46  * struct qobj_nodetype_cli { ... }
  47  * #endif
  48  */
  49 #ifndef HAVE_QOBJ_NODETYPE_CLI
  50 #define HAVE_QOBJ_NODETYPE_CLI -1
  51 struct qobj_nodetype_cli {
  52         int dummy;
  53 };
  54 #endif
  55
  56 #ifndef HAVE_QOBJ_NODETYPE_CAPNP
  57 #define HAVE_QOBJ_NODETYPE_CAPNP -1
  58 struct qobj_nodetype_capnp {
  59         int dummy;
  60 };
  61 #endif
  62
  63 #include "typesafe.h"
  64
  65 /* each different kind of object will have a global variable of this type,
  66  * which can be used by various other pieces to store type-related bits.
  67  * type equality can be tested as pointer equality. (cf. QOBJ_GET_TYPESAFE)
  68  */
  69 struct qobj_nodetype {
  70         ptrdiff_t node_member_offset;
  71         RESERVED_SPACE_STRUCT(qobj_nodetype_cli, cli, 256)
  72         RESERVED_SPACE_STRUCT(qobj_nodetype_capnp, capnp, 256)
  73 };
  74
  75 PREDECL_HASH(qobj_nodes);
  76
  77 /* anchor to be embedded somewhere in the object's struct */
  78 struct qobj_node {
  79         uint64_t nid;
  80         struct qobj_nodes_item nodehash;
  81         const struct qobj_nodetype *type;
  82 };
  83
  84 #define QOBJ_FIELDS struct qobj_node qobj_node
  85
  86 /* call these at the end of any _create function (QOBJ_REG)
  87  * and beginning of any _destroy function (QOBJ_UNREG) */
  88 #define QOBJ_REG(n, structname) qobj_reg(&n->qobj_node, &qobj_t_##structname)
  89 #define QOBJ_UNREG(n) qobj_unreg(&n->qobj_node)
  90
  91 /* internals - should not be directly used without a good reason
  92  *
  93  * note: qobj_get is essentially never safe to use in MT context because
  94  * the object could be deleted by another thread -- and worse, it could be
  95  * of the "wrong" type and deleted.
  96  *
  97  * with qobj_get_typed, the type check is done under lock, which means that
  98  * it can be used as long as another lock prevents the deletion of objects
  99  * of the expected type.
 100  *
 101  * in the long this may need another touch, e.g. built-in per-object locking.
 102  */
 103 void qobj_reg(struct qobj_node *node, const struct qobj_nodetype *type);
 104 void qobj_unreg(struct qobj_node *node);
 105 struct qobj_node *qobj_get(uint64_t id);
 106 void *qobj_get_typed(uint64_t id, const struct qobj_nodetype *type);
 107
 108 /* type declarations */
 109 #define DECLARE_QOBJ_TYPE(structname)                                          \
 110         extern const struct qobj_nodetype qobj_t_##structname                  \
 111         /* end */
 112 #define DEFINE_QOBJ_TYPE(structname)                                           \
 113         const struct qobj_nodetype qobj_t_##structname = {                     \
 114                 .node_member_offset =                                          \
 115                         (ptrdiff_t)offsetof(struct structname, qobj_node)}     \
 116         /* end */
 117 #define DEFINE_QOBJ_TYPE_INIT(structname, ...)                                 \
 118         const struct qobj_nodetype qobj_t_##structname = {                     \
 119                 .node_member_offset =                                          \
 120                         (ptrdiff_t)offsetof(struct structname, qobj_node),     \
 121                 __VA_ARGS__}                                                   \
 122         /* end */
 123
 124 /* ID dereference with typecheck.
 125  * will return NULL if id not found or wrong type. */
 126 #define QOBJ_GET_TYPESAFE(id, structname)                                      \
 127         ((struct structname *)qobj_get_typed((id), &qobj_t_##structname))
 128
 129 #define QOBJ_ID(ptr) ((ptr)->qobj_node.nid)
 130 #define QOBJ_ID_0SAFE(ptr)                                                     \
 131         ({                                                                     \
 132                 typeof(ptr) _ptr = (ptr);                                      \
 133                 _ptr ? _ptr->qobj_node.nid : 0ULL;                             \
 134         })
 135
 136 void qobj_init(void);
 137 void qobj_finish(void);
 138
 139 #ifdef __cplusplus
 140 }
 141 #endif
 142
 143 #endif /* _QOBJ_H */