[libvirt] [PATCH] tools: console: Relax stream EOF handling

[Roman Bolshakov]

On Thu, Aug 08, 2019 at 03:00:27PM -0300, Daniel Henrique Barboza wrote:
> (CCing Nikolay Shirokovskiy, author of  29f2b5248c )
> 
> On 8/7/19 8:34 AM, Roman Bolshakov wrote:
> > An attempt to poweroff a VM from inside triggers the error for existing
> > session of virsh console and it returns with non-zero exit code:
> >    error: internal error: console stream EOF
> > 
> > The message and status code are misleading because there's no real
> > error.
> > 
> > Fixes: 29f2b5248c6 ("tools: console: pass stream/fd errors to user")
> > Signed-off-by: Roman Bolshakov <r.bolshakov at yadro.com>
> > ---
> >   tools/virsh-console.c | 4 ----
> >   1 file changed, 4 deletions(-)
> > 
> > diff --git a/tools/virsh-console.c b/tools/virsh-console.c
> > index e16f841e57..408a745b0f 100644
> > --- a/tools/virsh-console.c
> > +++ b/tools/virsh-console.c
> > @@ -172,10 +172,6 @@ virConsoleEventOnStream(virStreamPtr st,
> >           if (got == -2)
> >               goto cleanup; /* blocking */
> >           if (got <= 0) {
> > -            if (got == 0)
> > -                virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
> > -                               _("console stream EOF"));
> > -
> 
> I appreciate if we can remove the 'console stream EOF' error message
> that started to appear even in regular VM shutdown, but I'm not sure
> if this is the right fix.
> 
> 'got' is the result of virStreamRecv(). Seeing the code documentation of
> this function we have:
> 
> (src/libvirt-stream.c)
> 
>  * Returns the number of bytes read, which may be less
>  * than requested.
>  *
>  * Returns 0 when the end of the stream is reached, at
>  * which time the caller should invoke virStreamFinish()
>  * to get confirmation of stream completion.
>  *
>  * Returns -1 upon error [....]
> 
> 
> And this is the doc for virStreamFinish():
> 
>  * 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.
> 
> 
> In the existing code we're not calling 'virStreamFinish()' to assert whether
> the got=0 from virStreamRecv is a successful shutdown or not, we're
> simply reporting an internal error assuming that something went wrong.
> 
> Shouldn't we call virStreamFinish if got=0 and only report an error if
> virStreamFinish returns -1? Does that suffice to fix this error message
> being thrown when the VM does a regular shutdown?
> 

That sounds right. virConsoleShutdown can be changed to take second
boolean parameter - needAbort and virStreamAbort will be invoked if
abort is needed on the stream. Otherwise, if EOF has been received,
virStreamFinish is called on the stream.

The need to call one of the functions is documented in virStreamNew:
   If a data stream has been used, then the application must call
   virStreamFinish or virStreamAbort before free'ing to, in order to
   notify the driver of termination.

As of now virConsoleShutdown doesn't print an error if virStreamAbort
fails. I can add them in v2 for both virStreamFinish and virStreamAbort.

Thanks,
Roman