Re: [Qemu-devel] [PATCH 1/7] virtio-console: Also throttle when less was written then requested

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 04/02/2013 12:40 PM, Amit Shah wrote:
> On (Mon) 01 Apr 2013 [18:00:55], Hans de Goede wrote:
>> Hi,
>>
>> On 03/29/2013 10:31 AM, Amit Shah wrote:
>>> On (Thu) 28 Mar 2013 [14:28:11], Hans de Goede wrote:
>>>> This is necessary so that we get properly woken up to write the rest.
>>>>
>>>> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
>>>> Acked-by: Amit Shah <amit.shah@redhat.com>
>>>> ---
>>>>   hw/virtio-console.c | 5 +++--
>>>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/hw/virtio-console.c b/hw/virtio-console.c
>>>> index 284180f..015947c 100644
>>>> --- a/hw/virtio-console.c
>>>> +++ b/hw/virtio-console.c
>>>> @@ -47,7 +47,7 @@ static ssize_t flush_buf(VirtIOSerialPort *port, const uint8_t *buf, size_t len)
>>>>       ret = qemu_chr_fe_write(vcon->chr, buf, len);
>>>>       trace_virtio_console_flush_buf(port->id, len, ret);
>>>>
>>>> -    if (ret <= 0) {
>>>> +    if (ret < len) {
>>>
>>> Oops, there's a conversion bug here: len is size_t, and ret is
>>> ssize_t.  Both need to be the same type.
>>>
>>> Since we're not returning negative, ret should be changed to size_t.
>>> The function signature changes too, but that's alright.
>>
>> Erm changing ret to a size_t will break things, since qemu_chr_fe_write can
>> return < 0 and storing that into an unsigned will change it into a very
>> large value instead ...
>
> Oh, definitely.  I meant changing the return type of flush_buf(), but
> that doesn't help matters much...
>
>> A better fix would be to change len to ssize_t. Although that will cause
>> issues if we ever get a single buf which is larger then 2^31 - 1. Note
>> we already have that problem since qemu_chr_fe_write already cannot handle
>> such large buffers...
>
> Yep.  Do you want to do that as part of this series?

Yes, I'll send a v2 of this patch incorporating the change for Gerd to
pick up.

Regards,

Hans