[Qemu-devel] [PATCH v2 52/52] usbaudio: change playback counters to 64 bit

From: "Kővágó, Zoltán" <dirty.ice.hu@gmail.com>
To: qemu-devel@nongnu.org
Cc: Gerd Hoffmann <kraxel@redhat.com>
Subject: [Qemu-devel] [PATCH v2 52/52] usbaudio: change playback counters to 64 bit
Date: Sun, 23 Dec 2018 21:52:28 +0100	[thread overview]
Message-ID: <1415d73f73787a48532cc6cdd3c2a5a0c2e02e2f.1545598229.git.DirtY.iCE.hu@gmail.com> (raw)
In-Reply-To: <cover.1545598229.git.DirtY.iCE.hu@gmail.com>

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>
---
 hw/usb/dev-audio.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/hw/usb/dev-audio.c b/hw/usb/dev-audio.c
index 29475a2b70..45ffc3ebb3 100644
--- a/hw/usb/dev-audio.c
+++ b/hw/usb/dev-audio.c
@@ -577,9 +577,9 @@ 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,
@@ -600,12 +600,14 @@ 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);
+    uint64_t free = buf->size - (buf->prod - buf->cons);
 
     if (free < USBAUDIO_PACKET_SIZE(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);
@@ -614,7 +616,7 @@ 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;
+    uint64_t used = buf->prod - buf->cons;
     uint8_t *data;
 
     if (!used) {
-- 
2.20.1
