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