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



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.

/**
 * 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


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