[libvirt] [PATCH v2] tools: console: Relax stream EOF handling

[Michal Privoznik]

On 8/13/19 12:01 AM, Daniel Henrique Barboza wrote:
> The comment I have here is that you're changing virConsoleShutdown
> API for all callers, with this new boolean value 'needAbort', because of a
> scenario (virStreamRecv being called before) that happens only on
> virConsoleEventOnStream.
> 
> 
> This is what I wondered in the review of the previous version of this
> patch:
> 
> "Shouldn't we call virStreamFinish if got=0 and only report an error if
> virStreamFinish returns -1?"
> 
> I tried it out and it worked like a charm for me:
> 
> 
> diff --git a/tools/virsh-console.c b/tools/virsh-console.c
> index e16f841..998662c 100644
> --- a/tools/virsh-console.c
> +++ b/tools/virsh-console.c
> @@ -172,9 +172,12 @@ virConsoleEventOnStream(virStreamPtr st,
>           if (got == -2)
>               goto cleanup; /* blocking */
>           if (got <= 0) {
> -            if (got == 0)
> -                virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
> -                               _("console stream EOF"));
> +            if (got == 0) {
> +                got = virStreamFinish(st);
> +                if (got != 0)
> +                    virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
> +                                   _("console stream EOF"));
> +            }
> 
>               virConsoleShutdown(con);
>               goto cleanup;
> 
> 
> I didn't see any errors by calling virStreamFinish() before 
> virStreamAbort()
> being called by virConsoleShutdown() right after (and by reading the code,
> it appears to be an OK usage), so I am skeptical about safeguarding the
> virStreamAbort() call with a boolean value like you're making here.
> 
> To be clear, I'm not saying your patch is wrong - and perhaps there is a 
> case
> for that safeguard inside virConsoleShutdown like you're doing here. My
> point here is that if the code I shown above isn't breaking anything, 
> I'd rather
> go for that.

I agree that this is better solution. One way to view libvirt streams is 
as a pipe. What is written on one side appears on the other. In the 
analogy, if a reader gets 0 bytes from the pipe on read() they know it's 
EOF and they call close() (or virStreamFinish() in this case).

Michal