usbaudio: change playback counters to 64 bit

With stereo playback, they need about 375 minutes of continuous audio
playback to overflow, which is usually not a problem (as stopping and
later resuming playback resets the counters).  But with 7.1 audio, they
only need about 95 minutes to overflow.

After the overflow, the buf->prod % USBAUDIO_PACKET_SIZE(channels)
assertion no longer holds true, which will result in overflowing the
buffer.  With 64 bit variables, it would take about 762000 years to
overflow.

Signed-off-by: Kővágó, Zoltán <DirtY.iCE.hu@gmail.com>
Message-id: ff866985ed369f1e18ea7c70da6a7fce8e241deb.1570996490.git.DirtY.iCE.hu@gmail.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

hw/usb/dev-audio.c

@@ -578,9 +578,9 @@ static const USBDesc desc_audio_multi = {
 
 struct streambuf {
     uint8_t *data;
-    uint32_t size;
-    uint32_t prod;
-    uint32_t cons;
+    size_t size;
+    uint64_t prod;
+    uint64_t cons;
 };
 
 static void streambuf_init(struct streambuf *buf, uint32_t size,
@@ -601,7 +601,7 @@ static void streambuf_fini(struct streambuf *buf)
 
 static int streambuf_put(struct streambuf *buf, USBPacket *p, uint32_t channels)
 {
-    uint32_t free = buf->size - (buf->prod - buf->cons);
+    int64_t free = buf->size - (buf->prod - buf->cons);
 
     if (free < USBAUDIO_PACKET_SIZE(channels)) {
         return 0;
@@ -610,6 +610,8 @@ static int streambuf_put(struct streambuf *buf, USBPacket *p, uint32_t channels)
         return 0;
     }
 
+    /* can happen if prod overflows */
+    assert(buf->prod % USBAUDIO_PACKET_SIZE(channels) == 0);
     usb_packet_copy(p, buf->data + (buf->prod % buf->size),
                     USBAUDIO_PACKET_SIZE(channels));
     buf->prod += USBAUDIO_PACKET_SIZE(channels);
@@ -618,10 +620,10 @@ static int streambuf_put(struct streambuf *buf, USBPacket *p, uint32_t channels)
 
 static uint8_t *streambuf_get(struct streambuf *buf, size_t *len)
 {
-    uint32_t used = buf->prod - buf->cons;
+    int64_t used = buf->prod - buf->cons;
     uint8_t *data;
 
-    if (!used) {
+    if (used <= 0) {
         *len = 0;
         return NULL;
     }