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Daniel P. Berrange88c5f202015-03-03 17:13:42 +00001/*
2 * QEMU generic buffers
3 *
4 * Copyright (c) 2015 Red Hat, Inc.
5 *
6 * This library is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU Lesser General Public
8 * License as published by the Free Software Foundation; either
Chetan Pant61f3c912020-10-23 12:44:24 +00009 * version 2.1 of the License, or (at your option) any later version.
Daniel P. Berrange88c5f202015-03-03 17:13:42 +000010 *
11 * This library is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * Lesser General Public License for more details.
15 *
16 * You should have received a copy of the GNU Lesser General Public
17 * License along with this library; if not, see <http://www.gnu.org/licenses/>.
18 *
19 */
20
Peter Maydellaafd7582016-01-29 17:49:55 +000021#include "qemu/osdep.h"
Paolo Bonzini87776ab2016-03-15 15:36:13 +010022#include "qemu/host-utils.h"
Daniel P. Berrange88c5f202015-03-03 17:13:42 +000023#include "qemu/buffer.h"
Gerd Hoffmannd2b90712015-10-30 12:10:01 +010024#include "trace.h"
Daniel P. Berrange88c5f202015-03-03 17:13:42 +000025
Gerd Hoffmann1ff36b52015-10-30 12:10:00 +010026#define BUFFER_MIN_INIT_SIZE 4096
27#define BUFFER_MIN_SHRINK_SIZE 65536
Peter Lieven5c10dbb2015-10-30 12:09:56 +010028
Wei Jiangangd43eda32016-03-14 17:58:29 +080029/* define the factor alpha for the exponential smoothing
Peter Lievenf14c3d82015-10-30 12:10:14 +010030 * that is used in the average size calculation. a shift
31 * of 7 results in an alpha of 1/2^7. */
32#define BUFFER_AVG_SIZE_SHIFT 7
33
Peter Lievenfd952432015-10-30 12:10:12 +010034static size_t buffer_req_size(Buffer *buffer, size_t len)
35{
36 return MAX(BUFFER_MIN_INIT_SIZE,
37 pow2ceil(buffer->offset + len));
38}
39
Peter Lieven4ec5ba12015-10-30 12:10:13 +010040static void buffer_adj_size(Buffer *buffer, size_t len)
41{
42 size_t old = buffer->capacity;
43 buffer->capacity = buffer_req_size(buffer, len);
44 buffer->buffer = g_realloc(buffer->buffer, buffer->capacity);
45 trace_buffer_resize(buffer->name ?: "unnamed",
46 old, buffer->capacity);
Peter Lievenf14c3d82015-10-30 12:10:14 +010047
48 /* make it even harder for the buffer to shrink, reset average size
Wei Jiangangd43eda32016-03-14 17:58:29 +080049 * to current capacity if it is larger than the average. */
Peter Lievenf14c3d82015-10-30 12:10:14 +010050 buffer->avg_size = MAX(buffer->avg_size,
51 buffer->capacity << BUFFER_AVG_SIZE_SHIFT);
Peter Lieven4ec5ba12015-10-30 12:10:13 +010052}
Peter Lievenfd952432015-10-30 12:10:12 +010053
Gerd Hoffmann810082d2015-10-30 12:09:57 +010054void buffer_init(Buffer *buffer, const char *name, ...)
55{
56 va_list ap;
57
58 va_start(ap, name);
59 buffer->name = g_strdup_vprintf(name, ap);
60 va_end(ap);
61}
62
Peter Lievenf14c3d82015-10-30 12:10:14 +010063static uint64_t buffer_get_avg_size(Buffer *buffer)
64{
65 return buffer->avg_size >> BUFFER_AVG_SIZE_SHIFT;
66}
67
Gerd Hoffmann1ff36b52015-10-30 12:10:00 +010068void buffer_shrink(Buffer *buffer)
69{
Peter Lievenf14c3d82015-10-30 12:10:14 +010070 size_t new;
71
72 /* Calculate the average size of the buffer as
73 * avg_size = avg_size * ( 1 - a ) + required_size * a
74 * where a is 1 / 2 ^ BUFFER_AVG_SIZE_SHIFT. */
75 buffer->avg_size *= (1 << BUFFER_AVG_SIZE_SHIFT) - 1;
76 buffer->avg_size >>= BUFFER_AVG_SIZE_SHIFT;
77 buffer->avg_size += buffer_req_size(buffer, 0);
78
79 /* And then only shrink if the average size of the buffer is much
80 * too big, to avoid bumping up & down the buffers all the time.
81 * realloc() isn't exactly cheap ... */
82 new = buffer_req_size(buffer, buffer_get_avg_size(buffer));
83 if (new < buffer->capacity >> 3 &&
84 new >= BUFFER_MIN_SHRINK_SIZE) {
85 buffer_adj_size(buffer, buffer_get_avg_size(buffer));
Gerd Hoffmann1ff36b52015-10-30 12:10:00 +010086 }
87
Peter Lieven4ec5ba12015-10-30 12:10:13 +010088 buffer_adj_size(buffer, 0);
Gerd Hoffmann1ff36b52015-10-30 12:10:00 +010089}
90
Daniel P. Berrange88c5f202015-03-03 17:13:42 +000091void buffer_reserve(Buffer *buffer, size_t len)
92{
93 if ((buffer->capacity - buffer->offset) < len) {
Peter Lieven4ec5ba12015-10-30 12:10:13 +010094 buffer_adj_size(buffer, len);
Daniel P. Berrange88c5f202015-03-03 17:13:42 +000095 }
96}
97
98gboolean buffer_empty(Buffer *buffer)
99{
100 return buffer->offset == 0;
101}
102
103uint8_t *buffer_end(Buffer *buffer)
104{
105 return buffer->buffer + buffer->offset;
106}
107
108void buffer_reset(Buffer *buffer)
109{
110 buffer->offset = 0;
Peter Lievenf14c3d82015-10-30 12:10:14 +0100111 buffer_shrink(buffer);
Daniel P. Berrange88c5f202015-03-03 17:13:42 +0000112}
113
114void buffer_free(Buffer *buffer)
115{
Gerd Hoffmannd2b90712015-10-30 12:10:01 +0100116 trace_buffer_free(buffer->name ?: "unnamed", buffer->capacity);
Daniel P. Berrange88c5f202015-03-03 17:13:42 +0000117 g_free(buffer->buffer);
Gerd Hoffmann810082d2015-10-30 12:09:57 +0100118 g_free(buffer->name);
Daniel P. Berrange88c5f202015-03-03 17:13:42 +0000119 buffer->offset = 0;
120 buffer->capacity = 0;
121 buffer->buffer = NULL;
Gerd Hoffmann810082d2015-10-30 12:09:57 +0100122 buffer->name = NULL;
Daniel P. Berrange88c5f202015-03-03 17:13:42 +0000123}
124
125void buffer_append(Buffer *buffer, const void *data, size_t len)
126{
127 memcpy(buffer->buffer + buffer->offset, data, len);
128 buffer->offset += len;
129}
130
131void buffer_advance(Buffer *buffer, size_t len)
132{
133 memmove(buffer->buffer, buffer->buffer + len,
134 (buffer->offset - len));
135 buffer->offset -= len;
Peter Lievenf14c3d82015-10-30 12:10:14 +0100136 buffer_shrink(buffer);
Daniel P. Berrange88c5f202015-03-03 17:13:42 +0000137}
Gerd Hoffmann4d1eb5f2015-10-30 12:09:58 +0100138
139void buffer_move_empty(Buffer *to, Buffer *from)
140{
Gerd Hoffmannd2b90712015-10-30 12:10:01 +0100141 trace_buffer_move_empty(to->name ?: "unnamed",
142 from->offset,
143 from->name ?: "unnamed");
Gerd Hoffmann4d1eb5f2015-10-30 12:09:58 +0100144 assert(to->offset == 0);
145
146 g_free(to->buffer);
147 to->offset = from->offset;
148 to->capacity = from->capacity;
149 to->buffer = from->buffer;
150
151 from->offset = 0;
152 from->capacity = 0;
153 from->buffer = NULL;
154}
Gerd Hoffmann830a9582015-10-30 12:09:59 +0100155
156void buffer_move(Buffer *to, Buffer *from)
157{
158 if (to->offset == 0) {
159 buffer_move_empty(to, from);
160 return;
161 }
162
Gerd Hoffmannd2b90712015-10-30 12:10:01 +0100163 trace_buffer_move(to->name ?: "unnamed",
164 from->offset,
165 from->name ?: "unnamed");
Gerd Hoffmann830a9582015-10-30 12:09:59 +0100166 buffer_reserve(to, from->offset);
167 buffer_append(to, from->buffer, from->offset);
168
169 g_free(from->buffer);
170 from->offset = 0;
171 from->capacity = 0;
172 from->buffer = NULL;
173}