1 files changed, 108 insertions, 2 deletions

diff --git a/util/buffer.c b/util/buffer.c
index cedd055680..8b27c08aac 100644
--- a/util/buffer.c
+++ b/util/buffer.c
@@ -19,12 +19,77 @@
  */
 
 #include "qemu/buffer.h"
+#include "trace.h"
+
+#define BUFFER_MIN_INIT_SIZE     4096
+#define BUFFER_MIN_SHRINK_SIZE  65536
+
+/* define the factor alpha for the expentional smoothing
+ * that is used in the average size calculation. a shift
+ * of 7 results in an alpha of 1/2^7. */
+#define BUFFER_AVG_SIZE_SHIFT       7
+
+static size_t buffer_req_size(Buffer *buffer, size_t len)
+{
+    return MAX(BUFFER_MIN_INIT_SIZE,
+               pow2ceil(buffer->offset + len));
+}
+
+static void buffer_adj_size(Buffer *buffer, size_t len)
+{
+    size_t old = buffer->capacity;
+    buffer->capacity = buffer_req_size(buffer, len);
+    buffer->buffer = g_realloc(buffer->buffer, buffer->capacity);
+    trace_buffer_resize(buffer->name ?: "unnamed",
+                        old, buffer->capacity);
+
+    /* make it even harder for the buffer to shrink, reset average size
+     * to currenty capacity if it is larger than the average. */
+    buffer->avg_size = MAX(buffer->avg_size,
+                           buffer->capacity << BUFFER_AVG_SIZE_SHIFT);
+}
+
+void buffer_init(Buffer *buffer, const char *name, ...)
+{
+    va_list ap;
+
+    va_start(ap, name);
+    buffer->name = g_strdup_vprintf(name, ap);
+    va_end(ap);
+}
+
+static uint64_t buffer_get_avg_size(Buffer *buffer)
+{
+    return buffer->avg_size >> BUFFER_AVG_SIZE_SHIFT;
+}
+
+void buffer_shrink(Buffer *buffer)
+{
+    size_t new;
+
+    /* Calculate the average size of the buffer as
+     * avg_size = avg_size * ( 1 - a ) + required_size * a
+     * where a is 1 / 2 ^ BUFFER_AVG_SIZE_SHIFT. */
+    buffer->avg_size *= (1 << BUFFER_AVG_SIZE_SHIFT) - 1;
+    buffer->avg_size >>= BUFFER_AVG_SIZE_SHIFT;
+    buffer->avg_size += buffer_req_size(buffer, 0);
+
+    /* And then only shrink if the average size of the buffer is much
+     * too big, to avoid bumping up & down the buffers all the time.
+     * realloc() isn't exactly cheap ...  */
+    new = buffer_req_size(buffer, buffer_get_avg_size(buffer));
+    if (new < buffer->capacity >> 3 &&
+        new >= BUFFER_MIN_SHRINK_SIZE) {
+        buffer_adj_size(buffer, buffer_get_avg_size(buffer));
+    }
+
+    buffer_adj_size(buffer, 0);
+}
 
 void buffer_reserve(Buffer *buffer, size_t len)
 {
     if ((buffer->capacity - buffer->offset) < len) {
-        buffer->capacity += (len + 1024);
-        buffer->buffer = g_realloc(buffer->buffer, buffer->capacity);
+        buffer_adj_size(buffer, len);
     }
 }
 
@@ -41,14 +106,18 @@ uint8_t *buffer_end(Buffer *buffer)
 void buffer_reset(Buffer *buffer)
 {
     buffer->offset = 0;
+    buffer_shrink(buffer);
 }
 
 void buffer_free(Buffer *buffer)
 {
+    trace_buffer_free(buffer->name ?: "unnamed", buffer->capacity);
     g_free(buffer->buffer);
+    g_free(buffer->name);
     buffer->offset = 0;
     buffer->capacity = 0;
     buffer->buffer = NULL;
+    buffer->name = NULL;
 }
 
 void buffer_append(Buffer *buffer, const void *data, size_t len)
@@ -62,4 +131,41 @@ void buffer_advance(Buffer *buffer, size_t len)
     memmove(buffer->buffer, buffer->buffer + len,
             (buffer->offset - len));
     buffer->offset -= len;
+    buffer_shrink(buffer);
+}
+
+void buffer_move_empty(Buffer *to, Buffer *from)
+{
+    trace_buffer_move_empty(to->name ?: "unnamed",
+                            from->offset,
+                            from->name ?: "unnamed");
+    assert(to->offset == 0);
+
+    g_free(to->buffer);
+    to->offset = from->offset;
+    to->capacity = from->capacity;
+    to->buffer = from->buffer;
+
+    from->offset = 0;
+    from->capacity = 0;
+    from->buffer = NULL;
+}
+
+void buffer_move(Buffer *to, Buffer *from)
+{
+    if (to->offset == 0) {
+        buffer_move_empty(to, from);
+        return;
+    }
+
+    trace_buffer_move(to->name ?: "unnamed",
+                      from->offset,
+                      from->name ?: "unnamed");
+    buffer_reserve(to, from->offset);
+    buffer_append(to, from->buffer, from->offset);
+
+    g_free(from->buffer);
+    from->offset = 0;
+    from->capacity = 0;
+    from->buffer = NULL;
 }