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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [PATCH v8 7/7] virtio-console: Enable port
	throttling when chardev is slow to consume data
Date: Wed, 1 Dec 2010 11:30:58 +0000
References: <cover.1291196789.git.amit.shah@redhat.com>
	<90e8c0b7db1086c38283f684a159a892b4a66228.1291196789.git.amit.shah@redhat.com>
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To: qemu-devel@nongnu.org
Cc: Amit Shah <amit.shah@redhat.com>, Gerd Hoffmann <kraxel@redhat.com>, Juan Quintela <quintela@redhat.com>

>  /* Callback function that's called when the guest sends us data */
>  static void flush_buf(VirtIOSerialPort *port, const uint8_t *buf, size_t
> len) {
>      VirtConsole *vcon = DO_UPCAST(VirtConsole, port, port);
> +    int ret;
> 
> -    qemu_chr_write(vcon->chr, buf, len);
> +    ret = qemu_chr_write(vcon->chr, buf, len);
> +    if (ret == -EAGAIN) {
> +        virtio_serial_throttle_port(port, true);
> +    }
>  }

This looks wrong. It will loose data in the case of a partial write
(i.e. ret < len)

Paul