[libvirt] error: server response too large
Daniel P. Berrange
berrange at redhat.com
Mon Oct 7 10:31:48 UTC 2013
On Mon, Oct 07, 2013 at 12:23:44PM +0200, Claudio Bley wrote:
> At Tue, 1 Oct 2013 17:19:56 +0100,
> Daniel P. Berrange wrote:
> >
> > On Tue, Oct 01, 2013 at 06:13:10PM +0200, Viktor Mihajlovski wrote:
> > > On 10/01/2013 03:02 PM, Daniel P. Berrange wrote:
> > > >On Mon, Sep 30, 2013 at 04:24:49PM +0100, Daniel P. Berrange wrote:
> > > >>On Mon, Sep 30, 2013 at 05:23:33PM +0200, Michal Privoznik wrote:
> > > >>>On 30.09.2013 17:02, Claudio Bley wrote:
> > > >>>>Hi.
> > > >>>>
> > > >>>>When trying to do a screenshot of a remote domain connected via
> > > >>>>qemu+tcp (for testing purposes only), I receive this error:
> > > >>>>
> > > >>>>----------------------------------------------------------------------
> > > >>>>virsh -c qemu+tcp://dev/system
> > > >>>>Welcome to virsh, the virtualization interactive terminal.
> > > >>>>
> > > >>>>Type: 'help' for help with commands
> > > >>>> 'quit' to quit
> > > >>>>
> > > >>>>virsh # version
> > > >>>>Compiled against library: libvir 0.9.8
> > > >>>>Using library: libvir 0.9.8
> > > >>>>Using API: QEMU 0.9.8
> > > >>>>Running hypervisor: QEMU 1.5.1
> > > >>>>
> > > >>>>virsh # screenshot 2 /tmp/screendump
> > > >>>>error: could not receive data from domain 2
> > > >>>>error: packet 1048600 bytes received from server too large, want 262144
> > > >>>>
> > > >>>>virsh # 2013-09-30 14:47:05.158+0000: 21646: info : libvirt version: 0.9.8
> > > >>>>2013-09-30 14:47:05.158+0000: 21646: warning : virNetClientIncomingEvent:1660 : Something went wrong during async message processing
> > > >>>>----------------------------------------------------------------------
> > > >>>>
> > > >>>>I'm using Ubuntu LTS 12.04.3, latest version in the repo which is
> > > >>>>0.9.8-2ubuntu17.13.
> > > >>>
> > > >This problem was fixed in
> > > >
> > > >commit 27e81517a876dcb738dd8a9bb2e0e68d71c3b7e3
> > > >Author: Daniel P. Berrange <berrange at redhat.com>
> > > >Date: Mon Sep 30 17:27:51 2013 +0100
> > > >
> > > > Fix max stream packet size for old clients
> > > >
> > > > The libvirtd server pushes data out to clients. It does not
> > > > know what protocol version the client might have, so must be
> > > > conservative and use the old payload limits. ie send no more
> > > > than 256kb of data per packet.
> > > >
> > > >
> > > >And backported to stable branches.
> > > >
> > > I tried libvirt 1.1.3 containing the commit on the server and
> > > Ubuntu libvirt 0.9.8 as the client and still have the issue
> > > if the message is greater than 256KB. The problem is that
> > > the old client checks the message size during decode (which is
> > > greater than the client's max message size).
> > >
> > > Not sure how to get out of this ...
> >
> > What were you doing to get a message greater than 256KB ? This
> > patch did not attempt to fix all possible combinations. If a
> > API call such as virConnectListAllDomains has so much data that
> > it requires > 256KB to encode, this fix won't solve that. There
> > is nothing we can do for API calls which have a genuine need to
> > exceed the old size limit.
> >
> > I was only addressing the case of virStreamPtr data which was
> > mistakenly hardcoded in the server to try sending 16 MB of data
> > at once. I switched it to only try to send 256 KB of data per
> > stream packet.
>
> I've also tested your patch, and it seems 256 KB of data is still a
> bit too large:
>
> virsh # screenshot 2 /tmp/test
> error: could not receive data from domain 2
> error: packet 262168 bytes received from server too large, want 262144
>
> The max payload size is computed as:
>
> VIR_NET_MESSAGE_MAX = 16777216
> VIR_NET_MESSAGE_HEADER_MAX = 24
> VIR_NET_MESSAGE_PAYLOAD_MAX = (VIR_NET_MESSAGE_MAX - VIR_NET_MESSAGE_HEADER_MAX) = 16777192
>
> So, it seems the legacy max payload size is actually 262120; I tested
> it and it works.
>
> ------------------- 8< ------ >8 ---------------------------
> Subject: [PATCH] Adjust legacy max payload size to account for header
> information
> Organization: AV-Test GmbH, Germany
>
> Commit 27e81517a87 set the payload size to 256 KB, which is
> actually the max packet size, including the size of the header.
>
> Reduce this by VIR_NET_MESSAGE_HEADER_MAX (24) and set
> VIR_NET_MESSAGE_LEGACY_PAYLOAD_MAX to 262120.
>
> Signed-off-by: Claudio Bley <cbley at av-test.de>
> ---
> src/rpc/virnetprotocol.x | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/src/rpc/virnetprotocol.x b/src/rpc/virnetprotocol.x
> index 1eae7cb..7b6f753 100644
> --- a/src/rpc/virnetprotocol.x
> +++ b/src/rpc/virnetprotocol.x
> @@ -55,7 +55,7 @@ const VIR_NET_MESSAGE_INITIAL = 65536;
> * payload size. We need to remember this for compat with
> * old clients.
> */
> -const VIR_NET_MESSAGE_LEGACY_PAYLOAD_MAX = 262144;
> +const VIR_NET_MESSAGE_LEGACY_PAYLOAD_MAX = 262120;
>
> /* Maximum total message size (serialised). */
> const VIR_NET_MESSAGE_MAX = 16777216;
Damn, yes, you are correct. The original value was 262120, I
copied the wrong value.
THe commit which changed it first was
commit eb635de1fed3257c5c62b552d1ec981c9545c1d7
Author: Michal Privoznik <mprivozn at redhat.com>
Date: Fri Apr 27 14:49:48 2012 +0200
rpc: Size up RPC limits
/* Size of message payload */
-const VIR_NET_MESSAGE_PAYLOAD_MAX = 262120;
+const VIR_NET_MESSAGE_PAYLOAD_MAX = 4194280;
Daniel
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