[libvirt-users] stream finish throws exception via python API

[Shahar Havivi]

On 26.04.16 15:30, Shahar Havivi wrote:
> On 26.04.16 14:14, Shahar Havivi wrote:
> > On 25.04.16 09:11, Cole Robinson wrote:
> > > On 04/25/2016 08:10 AM, Shahar Havivi wrote:
> > > > On 17.04.16 15:41, Shahar Havivi wrote:
> > > >> Hi,
> > > >> The following snippet works fine e.g. receiving the data but when calling
> > > >> stream.finish() we get the following error:
> > > >>
> > > >> stream = con.newStream()
> > > >> vol.download(stream, 0, 0, 0)
> > > >> buf = stream.recv(1024)
> > > >> stream.finish()
> > > >>
> > > >> libvirt: I/O Stream Utils error : internal error: I/O helper exited abnormally
> > > >> Traceback (most recent call last):
> > > >>   File "./helpers/kvm2ovirt", line 149, in <module>
> > > >>     download_volume(vol, item[1], diskno, disksitems, pksize)
> > > >>   File "./helpers/kvm2ovirt", line 102, in download_volume
> > > >>     stream.finish()
> > > >>   File "/usr/lib64/python2.7/site-packages/libvirt.py", line 5501, in finish
> > > >>     if ret == -1: raise libvirtError ('virStreamFinish() failed')
> > > >> libvirt.libvirtError: internal error: I/O helper exited abnormally
> > > >>  
> > > 
> > > The error message sucks, I'll send patches to improve it a little at least.
> > > 
> > > What's happening here is that the you haven't read all the data you requested
> > > (it's vol.download(path, offset, length, flags), length == 0 means read the
> > > whole file which I suspect you haven't done). In this case the iohelper
> > > program that libvirt uses won't complete feeding us all the data, and it exits
> > > with SIGPIPE when we close the read end of the pipe.
> > > 
> > > Now whether that should actually be an error condition is open to debate.
> > > virStreamFinish docs make it sound like it's legitimate to throw an error if
> > > it appears that all requested data wasn't read.
> > Thanks checking...
> Thanks Cole,
> I modify our script and for checking if stream.recv() returns zero the finish
> works fine.
> Our API needs to know the size of bytes that you are going to stream back
> which is not provided by the allocation and capacity.
> (ie the same as du -s /path/to/disk)
> 
>   Shahar.
We need the size of the image "Image end offset" you get from "qemu-img check",
Does libvirt have an API for that?

Thanks,
  Shahar.

> > > 
> > > /**
> > >  * virStreamFinish:
> > >  * @stream: pointer to the stream object
> > >  *
> > >  * Indicate that there is no further data to be transmitted
> > >  * on the stream. For output streams this should be called once
> > >  * all data has been written. For input streams this should be
> > >  * called once virStreamRecv returns end-of-file.
> > >  *
> > >  * This method is a synchronization point for all asynchronous
> > >  * errors, so if this returns a success code the application can
> > >  * be sure that all data has been successfully processed.
> > >  *
> > >  * Returns 0 on success, -1 upon error
> > >  */
> > > 
> > > So maybe in your case you want virStreamAbort instead (which also
> > > unconditionally throws an error which is also an issue IMO but can be ignored)
> > > 
> > > CCing danpb for this thoughts on the erroring semantics
> > > 
> > > - Cole