fsdev/p9array.h

   1 /*
   2  * P9Array - deep auto free C-array
   3  *
   4  * Copyright (c) 2021 Crudebyte
   5  *
   6  * Authors:
   7  *   Christian Schoenebeck <qemu_oss@crudebyte.com>
   8  *
   9  * Permission is hereby granted, free of charge, to any person obtaining a copy
  10  * of this software and associated documentation files (the "Software"), to deal
  11  * in the Software without restriction, including without limitation the rights
  12  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  13  * copies of the Software, and to permit persons to whom the Software is
  14  * furnished to do so, subject to the following conditions:
  15  *
  16  * The above copyright notice and this permission notice shall be included in
  17  * all copies or substantial portions of the Software.
  18  *
  19  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  20  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  21  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
  22  * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  23  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  24  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  25  * THE SOFTWARE.
  26  */
  27 #ifndef QEMU_P9ARRAY_H
  28 #define QEMU_P9ARRAY_H
  29
  30 #include "qemu/compiler.h"
  31
  32 /**
  33  * P9Array provides a mechanism to access arrays in common C-style (e.g. by
  34  * square bracket [] operator) in conjunction with reference variables that
  35  * perform deep auto free of the array when leaving the scope of the auto
  36  * reference variable. That means not only is the array itself automatically
  37  * freed, but also memory dynamically allocated by the individual array
  38  * elements.
  39  *
  40  * Example:
  41  *
  42  * Consider the following user struct @c Foo which shall be used as scalar
  43  * (element) type of an array:
  44  * @code
  45  * typedef struct Foo {
  46  *     int i;
  47  *     char *s;
  48  * } Foo;
  49  * @endcode
  50  * and assume it has the following function to free memory allocated by @c Foo
  51  * instances:
  52  * @code
  53  * void free_foo(Foo *foo) {
  54  *     free(foo->s);
  55  * }
  56  * @endcode
  57  * Add the following to a shared header file:
  58  * @code
  59  * P9ARRAY_DECLARE_TYPE(Foo);
  60  * @endcode
  61  * and the following to a C unit file:
  62  * @code
  63  * P9ARRAY_DEFINE_TYPE(Foo, free_foo);
  64  * @endcode
  65  * Finally the array may then be used like this:
  66  * @code
  67  * void doSomething(size_t n) {
  68  *     P9ARRAY_REF(Foo) foos = NULL;
  69  *     P9ARRAY_NEW(Foo, foos, n);
  70  *     for (size_t i = 0; i < n; ++i) {
  71  *         foos[i].i = i;
  72  *         foos[i].s = calloc(4096, 1);
  73  *         snprintf(foos[i].s, 4096, "foo %d", i);
  74  *         if (...) {
  75  *             return; // array auto freed here
  76  *         }
  77  *     }
  78  *     // array auto freed here
  79  * }
  80  * @endcode
  81  */
  82
  83 /**
  84  * Declares an array type for the passed @a scalar_type.
  85  *
  86  * This is typically used from a shared header file.
  87  *
  88  * @param scalar_type - type of the individual array elements
  89  */
  90 #define P9ARRAY_DECLARE_TYPE(scalar_type) \
  91     typedef struct P9Array##scalar_type { \
  92         size_t len; \
  93         scalar_type first[]; \
  94     } P9Array##scalar_type; \
  95     \
  96     void p9array_new_##scalar_type(scalar_type **auto_var, size_t len); \
  97     void p9array_auto_free_##scalar_type(scalar_type **auto_var); \
  98
  99 /**
 100  * Defines an array type for the passed @a scalar_type and appropriate
 101  * @a scalar_cleanup_func.
 102  *
 103  * This is typically used from a C unit file.
 104  *
 105  * @param scalar_type - type of the individual array elements
 106  * @param scalar_cleanup_func - appropriate function to free memory dynamically
 107  *                              allocated by individual array elements before
 108  */
 109 #define P9ARRAY_DEFINE_TYPE(scalar_type, scalar_cleanup_func) \
 110     void p9array_new_##scalar_type(scalar_type **auto_var, size_t len) \
 111     { \
 112         p9array_auto_free_##scalar_type(auto_var); \
 113         P9Array##scalar_type *arr = g_malloc0(sizeof(P9Array##scalar_type) + \
 114             len * sizeof(scalar_type)); \
 115         arr->len = len; \
 116         *auto_var = &arr->first[0]; \
 117     } \
 118     \
 119     void p9array_auto_free_##scalar_type(scalar_type **auto_var) \
 120     { \
 121         scalar_type *first = (*auto_var); \
 122         if (!first) { \
 123             return; \
 124         } \
 125         P9Array##scalar_type *arr = (P9Array##scalar_type *) ( \
 126             ((char *)first) - offsetof(P9Array##scalar_type, first) \
 127         ); \
 128         for (size_t i = 0; i < arr->len; ++i) { \
 129             scalar_cleanup_func(&arr->first[i]); \
 130         } \
 131         g_free(arr); \
 132     } \
 133
 134 /**
 135  * Used to declare a reference variable (unique pointer) for an array. After
 136  * leaving the scope of the reference variable, the associated array is
 137  * automatically freed.
 138  *
 139  * @param scalar_type - type of the individual array elements
 140  */
 141 #define P9ARRAY_REF(scalar_type) \
 142     __attribute((__cleanup__(p9array_auto_free_##scalar_type))) scalar_type*
 143
 144 /**
 145  * Allocates a new array of passed @a scalar_type with @a len number of array
 146  * elements and assigns the created array to the reference variable
 147  * @a auto_var.
 148  *
 149  * @param scalar_type - type of the individual array elements
 150  * @param auto_var - destination reference variable
 151  * @param len - amount of array elements to be allocated immediately
 152  */
 153 #define P9ARRAY_NEW(scalar_type, auto_var, len) \
 154     QEMU_BUILD_BUG_MSG( \
 155         !__builtin_types_compatible_p(scalar_type, typeof(*auto_var)), \
 156         "P9Array scalar type mismatch" \
 157     ); \
 158     p9array_new_##scalar_type((&auto_var), len)
 159
 160 #endif /* QEMU_P9ARRAY_H */