[Qemu-devel] [PULL 2/8] msmouse: fix buffer handling

[Gerd Hoffmann <kraxel@redhat.com>]

The msmouse chardev backend writes data without checking whenever there
is enough space.

That happens to work with linux guests, probably by pure luck because
the linux driver enables the fifo and the serial port emulation accepts
more data than announced via qemu_chr_be_can_write() in that case.

Handle this properly by adding a buffer to MouseState.  Hook up a
CharDriverState->accept_input() handler which feeds the buffer to the
serial port.  msmouse_event() only fills the buffer now, and calls the
accept_input handler too to kick off the transmission.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1467625375-31774-3-git-send-email-kraxel@redhat.com
---
 backends/msmouse.c | 40 +++++++++++++++++++++++++++++++++++-----
 1 file changed, 35 insertions(+), 5 deletions(-)

diff --git a/backends/msmouse.c b/backends/msmouse.c
index 731784f..9ade31b 100644
--- a/backends/msmouse.c
+++ b/backends/msmouse.c
@@ -32,13 +32,35 @@
 typedef struct {
     CharDriverState *chr;
     QEMUPutMouseEntry *entry;
+    uint8_t outbuf[32];
+    int outlen;
 } MouseState;
 
+static void msmouse_chr_accept_input(CharDriverState *chr)
+{
+    MouseState *mouse = chr->opaque;
+    int len;
+
+    len = qemu_chr_be_can_write(chr);
+    if (len > mouse->outlen) {
+        len = mouse->outlen;
+    }
+    if (!len) {
+        return;
+    }
+
+    qemu_chr_be_write(chr, mouse->outbuf, len);
+    mouse->outlen -= len;
+    if (mouse->outlen) {
+        memmove(mouse->outbuf, mouse->outbuf + len, mouse->outlen);
+    }
+}
+
 static void msmouse_event(void *opaque,
                           int dx, int dy, int dz, int buttons_state)
 {
     CharDriverState *chr = (CharDriverState *)opaque;
-
+    MouseState *mouse = chr->opaque;
     unsigned char bytes[4] = { 0x40, 0x00, 0x00, 0x00 };
 
     /* Movement deltas */
@@ -51,10 +73,17 @@ static void msmouse_event(void *opaque,
     bytes[0] |= (buttons_state & 0x02 ? 0x10 : 0x00);
     bytes[3] |= (buttons_state & 0x04 ? 0x20 : 0x00);
 
-    /* We always send the packet of, so that we do not have to keep track
-       of previous state of the middle button. This can potentially confuse
-       some very old drivers for two button mice though. */
-    qemu_chr_be_write(chr, bytes, 4);
+    if (mouse->outlen <= sizeof(mouse->outbuf) - 4) {
+        /* We always send the packet of, so that we do not have to keep track
+           of previous state of the middle button. This can potentially confuse
+           some very old drivers for two button mice though. */
+        memcpy(mouse->outbuf + mouse->outlen, bytes, 4);
+        mouse->outlen += 4;
+    } else {
+        /* queue full -> drop event */
+    }
+
+    msmouse_chr_accept_input(chr);
 }
 
 static int msmouse_chr_write (struct CharDriverState *s, const uint8_t *buf, int len)
@@ -84,6 +113,7 @@ static CharDriverState *qemu_chr_open_msmouse(const char *id,
     chr = qemu_chr_alloc(common, errp);
     chr->chr_write = msmouse_chr_write;
     chr->chr_close = msmouse_chr_close;
+    chr->chr_accept_input = msmouse_chr_accept_input;
     chr->explicit_be_open = true;
 
     mouse = g_new0(MouseState, 1);
-- 
1.8.3.1