src/common/dynamic-buffer.h

   1 /*
   2  * Copyright (C) 2017 Jérémie Galarneau <jeremie.galarneau@efficios.com>
   3  *
   4  * SPDX-License-Identifier: LGPL-2.1-only
   5  *
   6  */
   7
   8 #ifndef LTTNG_DYNAMIC_BUFFER_H
   9 #define LTTNG_DYNAMIC_BUFFER_H
  10
  11 #include <stddef.h>
  12 #include <stdint.h>
  13 #include <common/macros.h>
  14
  15 #ifdef __cplusplus
  16 extern "C" {
  17 #endif
  18
  19 struct lttng_buffer_view;
  20
  21 struct lttng_dynamic_buffer {
  22         char *data;
  23         /* size is the buffer's currently used capacity. */
  24         size_t size;
  25         /*
  26          * capacity shall not be accessed by users directly, it is meant for
  27          * internal use only.
  28          */
  29         size_t _capacity;
  30 };
  31
  32 /*
  33  * Initialize a dynamic buffer. This performs no allocation and is meant
  34  * to be used instead of memset or explicit initialization of the buffer.
  35  */
  36 void lttng_dynamic_buffer_init(struct lttng_dynamic_buffer *buffer);
  37
  38 /*
  39  * Append the content of a raw memory buffer to the end of a dynamic buffer
  40  * (after its current "size"). The dynamic buffer's size is increased by
  41  * "len", and its capacity is adjusted automatically.
  42  */
  43 int lttng_dynamic_buffer_append(struct lttng_dynamic_buffer *buffer,
  44                 const void *buf, size_t len);
  45
  46 /*
  47  * Performs the same action as lttng_dynamic_buffer_append(), but using another
  48  * dynamic buffer as the source buffer. The source buffer's size is used in lieu
  49  * of "len".
  50  */
  51 int lttng_dynamic_buffer_append_buffer(struct lttng_dynamic_buffer *dst_buffer,
  52                 const struct lttng_dynamic_buffer *src_buffer);
  53
  54 /*
  55  * Performs the same action as lttng_dynamic_buffer_append(), but using a
  56  * buffer view as the source buffer. The source buffer's size is used in lieu
  57  * of "len".
  58  */
  59 int lttng_dynamic_buffer_append_view(struct lttng_dynamic_buffer *buffer,
  60                 const struct lttng_buffer_view *view);
  61
  62 /*
  63  * Set the buffer's size to new_size. The capacity of the buffer will
  64  * be expanded (if necessary) to accommodates new_size. Areas acquired by
  65  * a size increase will be zeroed.
  66  *
  67  * Be careful to expand the buffer's size _before_ calling out external
  68  * APIs (e.g. read(3)) which may populate the buffer as setting the size
  69  * after will zero-out the result of the operation.
  70  *
  71  * Shrinking a buffer does not zero the old content. If the buffer may contain
  72  * sensititve information, it must be cleared manually _before_ changing the
  73  * size.
  74  *
  75  * NOTE: It is striclty _invalid_ to access memory after _size_, regardless
  76  *       of prior calls to set_capacity().
  77  */
  78 int lttng_dynamic_buffer_set_size(struct lttng_dynamic_buffer *buffer,
  79                 size_t new_size);
  80
  81 /*
  82  * Set the buffer's capacity to accommodates the new_capacity, allocating memory
  83  * as necessary. The buffer's content is preserved. Setting a buffer's capacity
  84  * is meant as a _hint_ to the underlying buffer and is only optimization; no
  85  * guarantee is offered that subsequent calls to append or set_size will succeed.
  86  *
  87  * If the current size > new_capacity, the operation will fail.
  88  */
  89 int lttng_dynamic_buffer_set_capacity(struct lttng_dynamic_buffer *buffer,
  90                 size_t new_capacity);
  91
  92 /* Release any memory used by the dynamic buffer. */
  93 void lttng_dynamic_buffer_reset(struct lttng_dynamic_buffer *buffer);
  94
  95 /* Get the space left in the buffer before a new resize is needed. */
  96 size_t lttng_dynamic_buffer_get_capacity_left(
  97                 struct lttng_dynamic_buffer *buffer);
  98
  99 #ifdef __cplusplus
 100 }
 101 #endif
 102
 103 #endif /* LTTNG_DYNAMIC_BUFFER_H */