src/common/dynamic-buffer.hpp

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