Re: [Qemu-devel] [PATCH for-2.6] nbd: Don't fail handshake on NBD_OPT_LIST descriptions

[Max Reitz]

On 15.04.2016 00:07, Eric Blake wrote:
> On 04/14/2016 03:31 PM, Max Reitz wrote:
>> On 08.04.2016 03:09, Eric Blake wrote:
>>> The NBD Protocol states that NBD_REP_SERVER may set
>>> 'length > sizeof(namelen) + namelen'; in which case the rest
>>> of the packet is a UTF-8 description of the export.  While we
>>> don't know of any NBD servers that send this description yet,
>>> we had better consume the data so we don't choke when we start
>>> to talk to such a server.
>>>
> 
>>> @@ -214,6 +219,20 @@ static int nbd_receive_list(QIOChannel *ioc, char 
>>> **name, Error **errp)
>>>              return -1;
>>>          }
>>>          (*name)[namelen] = '\0';
>>> +        len -= namelen;
>>> +        if (len) {
>>> +            char *buf = g_malloc(len + 1);
>>> +            if (read_sync(ioc, buf, len) != len) {
>>> +                error_setg(errp, "failed to read export description");
>>> +                g_free(*name);
>>> +                g_free(buf);
>>> +                *name = NULL;
>>> +                return -1;
>>> +            }
>>> +            buf[len] = '\0';
>>> +            TRACE("Ignoring export description: %s", buf);
>>
>> I find this funny, somehow.
>>
>> Perhaps it's because this may explicitly print something while
>> explaining that it's being ignored.
> 
> The server.c code had a nice function for skipping unwanted bytes;

I know; I added it. ;-)

>                                                                    and
> in a 2.7 series, I borrowed that idea:
> 
> https://lists.gnu.org/archive/html/qemu-devel/2016-04/msg01597.html
> 
> but for the purpose of minimal churn in 2.6, I don't mind the
> (temporary) oddity.

Yeah, I didn't mean funny in the "why is that here" sense, but in the "I
chuckled a little" sense. :-)

>>> +            g_free(buf);
>>> +        }
>>>      } else {
>>>          error_setg(errp, "Unexpected reply type %x expected %x",
>>>                     type, NBD_REP_SERVER);
>>>
>>
>> Thanks Eric, I applied this patch to my block branch (for 2.6). If this
>> was not your intention, please speak up. :-)
>>
>> https://github.com/XanClic/qemu/commits/block
> 
> You did the right thing.

That phrasing makes me feel a little uncomfortable. It's a phrase I'd
expect to hear after I have committed a deed of questionable morality,
which was right only in the greater scheme of things and for the
well-being of the many. So now I'm a bit worried. :-)

(Just kidding, of course.)

Max

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