src/common/dynamic-buffer.h

   1 /*
   2  * Copyright (C) 2017 - Jérémie Galarneau <jeremie.galarneau@efficios.com>
   3  *
   4  * This program is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU Lesser General Public License, version 2.1 only,
   6  * as published by the Free Software Foundation.
   7  *
   8  * This program is distributed in the hope that it will be useful, but WITHOUT
   9  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  10  * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
  11  * for more details.
  12  *
  13  * You should have received a copy of the GNU Lesser General Public License
  14  * along with this program; if not, write to the Free Software Foundation,
  15  * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  16  */
  17
  18 #ifndef LTTNG_DYNAMIC_BUFFER_H
  19 #define LTTNG_DYNAMIC_BUFFER_H
  20
  21 #include <stddef.h>
  22 #include <stdint.h>
  23
  24 struct lttng_dynamic_buffer {
  25         char *data;
  26         /* size is the buffer's currently used capacity. */
  27         size_t size;
  28         /*
  29          * capacity shall not be accessed by users directly, it is meant for
  30          * internal use only.
  31          */
  32         size_t _capacity;
  33 };
  34
  35 /*
  36  * Initialize a dynamic buffer. This performs no allocation and is meant
  37  * to be used instead of memset or explicit initialization of the buffer.
  38  */
  39 void lttng_dynamic_buffer_init(struct lttng_dynamic_buffer *buffer);
  40
  41 /*
  42  * Append the content of a raw memory buffer to the end of a dynamic buffer
  43  * (after its current "size"). The dynamic buffer's size is increased by
  44  * "len", and its capacity is adjusted automatically.
  45  */
  46 int lttng_dynamic_buffer_append(struct lttng_dynamic_buffer *buffer,
  47                 const void *buf, size_t len);
  48
  49 /*
  50  * Performs the same action as lttng_dynamic_buffer_append(), but using another
  51  * dynamic buffer as the source buffer. The source buffer's size is used in lieu
  52  * of "len".
  53  */
  54 int lttng_dynamic_buffer_append_buffer(struct lttng_dynamic_buffer *dst_buffer,
  55                 struct lttng_dynamic_buffer *src_buffer);
  56
  57 /*
  58  * Set the buffer's size to new_size. The capacity of the buffer will
  59  * be expanded (if necessary) to accomodate new_size. Areas acquired by
  60  * a size increase will be zeroed.
  61  *
  62  * Be careful to expand the buffer's size _before_ calling out external
  63  * APIs (e.g. read(3)) which may populate the buffer as setting the size
  64  * after will zero-out the result of the operation.
  65  *
  66  * Shrinking a buffer does not zero the old content. If the buffer may contain
  67  * sensititve information, it must be cleared manually _before_ changing the
  68  * size.
  69  *
  70  * NOTE: It is striclty _invalid_ to access memory after _size_, regardless
  71  *       of prior calls to set_capacity().
  72  */
  73 int lttng_dynamic_buffer_set_size(struct lttng_dynamic_buffer *buffer,
  74                 size_t new_size);
  75
  76 /*
  77  * Set the buffer's capacity to accomodate the new_capacity, allocating memory
  78  * as necessary. The buffer's content is preserved. Setting a buffer's capacity
  79  * is meant as a _hint_ to the underlying buffer and is only optimization; no
  80  * guarantee is offered that subsequent calls to append or set_size will succeed.
  81  *
  82  * If the current size > new_capacity, the operation will fail.
  83  */
  84 int lttng_dynamic_buffer_set_capacity(struct lttng_dynamic_buffer *buffer,
  85                 size_t new_capacity);
  86
  87 /* Release any memory used by the dynamic buffer. */
  88 void lttng_dynamic_buffer_reset(struct lttng_dynamic_buffer *buffer);
  89
  90 #endif /* LTTNG_DYNAMIC_BUFFER_H */