1 | /* |
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 |
9 | * version 2 of the License, or (at your option) any later version. |
10 | * |
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 | |
21 | #include "qemu/osdep.h" |
22 | #include "qemu/host-utils.h" |
23 | #include "qemu/buffer.h" |
24 | #include "trace.h" |
25 | |
26 | #define BUFFER_MIN_INIT_SIZE 4096 |
27 | #define BUFFER_MIN_SHRINK_SIZE 65536 |
28 | |
29 | /* define the factor alpha for the exponential smoothing |
30 | * 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 | |
34 | static 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 | |
40 | static 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); |
47 | |
48 | /* make it even harder for the buffer to shrink, reset average size |
49 | * to current capacity if it is larger than the average. */ |
50 | buffer->avg_size = MAX(buffer->avg_size, |
51 | buffer->capacity << BUFFER_AVG_SIZE_SHIFT); |
52 | } |
53 | |
54 | void 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 | |
63 | static uint64_t buffer_get_avg_size(Buffer *buffer) |
64 | { |
65 | return buffer->avg_size >> BUFFER_AVG_SIZE_SHIFT; |
66 | } |
67 | |
68 | void buffer_shrink(Buffer *buffer) |
69 | { |
70 | 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)); |
86 | } |
87 | |
88 | buffer_adj_size(buffer, 0); |
89 | } |
90 | |
91 | void buffer_reserve(Buffer *buffer, size_t len) |
92 | { |
93 | if ((buffer->capacity - buffer->offset) < len) { |
94 | buffer_adj_size(buffer, len); |
95 | } |
96 | } |
97 | |
98 | gboolean buffer_empty(Buffer *buffer) |
99 | { |
100 | return buffer->offset == 0; |
101 | } |
102 | |
103 | uint8_t *buffer_end(Buffer *buffer) |
104 | { |
105 | return buffer->buffer + buffer->offset; |
106 | } |
107 | |
108 | void buffer_reset(Buffer *buffer) |
109 | { |
110 | buffer->offset = 0; |
111 | buffer_shrink(buffer); |
112 | } |
113 | |
114 | void buffer_free(Buffer *buffer) |
115 | { |
116 | trace_buffer_free(buffer->name ?: "unnamed" , buffer->capacity); |
117 | g_free(buffer->buffer); |
118 | g_free(buffer->name); |
119 | buffer->offset = 0; |
120 | buffer->capacity = 0; |
121 | buffer->buffer = NULL; |
122 | buffer->name = NULL; |
123 | } |
124 | |
125 | void 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 | |
131 | void buffer_advance(Buffer *buffer, size_t len) |
132 | { |
133 | memmove(buffer->buffer, buffer->buffer + len, |
134 | (buffer->offset - len)); |
135 | buffer->offset -= len; |
136 | buffer_shrink(buffer); |
137 | } |
138 | |
139 | void buffer_move_empty(Buffer *to, Buffer *from) |
140 | { |
141 | trace_buffer_move_empty(to->name ?: "unnamed" , |
142 | from->offset, |
143 | from->name ?: "unnamed" ); |
144 | 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 | } |
155 | |
156 | void buffer_move(Buffer *to, Buffer *from) |
157 | { |
158 | if (to->offset == 0) { |
159 | buffer_move_empty(to, from); |
160 | return; |
161 | } |
162 | |
163 | trace_buffer_move(to->name ?: "unnamed" , |
164 | from->offset, |
165 | from->name ?: "unnamed" ); |
166 | 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 | } |
174 | |