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Date: Wed, 31 Mar 2010 15:53:59 +0200
From: Gerd Hoffmann <kraxel@redhat.com>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] [PATCH 15/17] virtio-serial: Apps should consume
	all	data that guest sends out / Fix virtio api abuse
References: <1270020848-15526-1-git-send-email-amit.shah@redhat.com>	<1270020848-15526-2-git-send-email-amit.shah@redhat.com>	<1270020848-15526-3-git-send-email-amit.shah@redhat.com>	<1270020848-15526-4-git-send-email-amit.shah@redhat.com>	<1270020848-15526-5-git-send-email-amit.shah@redhat.com>	<1270020848-15526-6-git-send-email-amit.shah@redhat.com>	<1270020848-15526-7-git-send-email-amit.shah@redhat.com>	<1270020848-15526-8-git-send-email-amit.shah@redhat.com>	<1270020848-15526-9-git-send-email-amit.shah@redhat.com>	<1270020848-15526-10-git-send-email-amit.shah@redhat.com>	<1270020848-15526-11-git-send-email-amit.shah@redhat.com>	<1270020848-15526-12-git-send-email-amit.shah@redhat.com>	<1270020848-15526-13-git-send-email-amit.shah@redhat.com>	<1270020848-15526-14-git-send-email-amit.shah@redhat.com>	<1270020848-15526-15-git-send-email-amit.shah@redhat.com>
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To: Amit Shah <amit.shah@redhat.com>
Cc: Juan Quintela <quintela@redhat.com>, qemu list <qemu-devel@nongnu.org>, "Michael S. Tsirkin" <mst@redhat.com>

>   /* Callback function that's called when the guest sends us data */
> -static size_t flush_buf(VirtIOSerialPort *port, const uint8_t *buf, size_t len)
> +static void flush_buf(VirtIOSerialPort *port, const uint8_t *buf, size_t len)
>   {
>       VirtConsole *vcon = DO_UPCAST(VirtConsole, port, port);
> -    ssize_t ret;
>
> -    ret = qemu_chr_write(vcon->chr, buf, len);
> -
> -    return ret<  0 ? 0 : ret;
> +    qemu_chr_write(vcon->chr, buf, len);
>   }

Ok, so we loose data in case qemu_chr_write wasn't able to write out all 
data?  Nice opportunity to show flow control in action here ;)

On failed+partial writes just put the remaining data into a buffer and 
throttle the port until all buffered data has been successfully written 
to the chardev.

Incremental patch is fine to avoid the chicken-egg issue (throttling is 
added by patch #17).

cheers,
   Gerd