Re: [PATCH 02/11] migration/hmp: Fix postcopy-blocktime per-vCPU results

[Markus Armbruster <armbru@redhat.com>]

Peter Xu <peterx@redhat.com> writes:

> Unfortunately, it was never correctly shown..
>
> This is only found when I started to look into making the blocktime feature
> more useful (so as to avoid using bpftrace, even though I'm not sure which
> one will be harder to use..).
>
> So the old dump would look like this:
>
>   Postcopy vCPU Blocktime: 0-1,4,10,21,33,46,48,59
>
> Even though there're actually 40 vcpus, and the string will merge same
> elements and also sort them.
>
> To fix it, simply loop over the uint32List manually.  Now it looks like:
>
>   Postcopy vCPU Blocktime (ms):
>    [15, 0, 0, 43, 29, 34, 36, 29, 37, 41,
>     33, 37, 45, 52, 50, 38, 40, 37, 40, 49,
>     40, 35, 35, 35, 81, 19, 18, 19, 18, 30,
>     22, 3, 0, 0, 0, 0, 0, 0, 0, 0]
>
> Cc: Dr. David Alan Gilbert <dave@treblig.org>
> Cc: Alexey Perevalov <a.perevalov@samsung.com>
> Cc: Markus Armbruster <armbru@redhat.com>
> Signed-off-by: Peter Xu <peterx@redhat.com>
> ---
>  migration/migration-hmp-cmds.c | 23 ++++++++++++++---------
>  1 file changed, 14 insertions(+), 9 deletions(-)
>
> diff --git a/migration/migration-hmp-cmds.c b/migration/migration-hmp-cmds.c
> index 367ff6037f..3cf890b887 100644
> --- a/migration/migration-hmp-cmds.c
> +++ b/migration/migration-hmp-cmds.c
> @@ -208,15 +208,20 @@ void hmp_info_migrate(Monitor *mon, const QDict *qdict)
>      }
>  
>      if (info->has_postcopy_vcpu_blocktime) {
> -        Visitor *v;
> -        char *str;
> -        v = string_output_visitor_new(false, &str);
> -        visit_type_uint32List(v, NULL, &info->postcopy_vcpu_blocktime,
> -                              &error_abort);
> -        visit_complete(v, &str);
> -        monitor_printf(mon, "Postcopy vCPU Blocktime: %s\n", str);
> -        g_free(str);
> -        visit_free(v);
> +        uint32List *item = info->postcopy_vcpu_blocktime;
> +        int count = 0;
> +
> +        monitor_printf(mon, "Postcopy vCPU Blocktime (ms): \n [");
> +
> +        while (item) {
> +            monitor_printf(mon, "%"PRIu32", ", item->value);
> +            item = item->next;
> +            /* Each line 10 vcpu results, newline if there's more */

The list can be arbitrarily long?

> +            if ((++count % 10 == 0) && item) {
> +                monitor_printf(mon, "\n  ");
> +            }
> +        }
> +        monitor_printf(mon, "\b\b]\n");

Uh, backspace?

I usually do something like

    sep = "";
    for (...) {
        printf("%s...", sep, ...);
        sep = ", "
    }

To add line breaks, I'd use something like

        sep = ... ? ", " : ",\n";

>      }
>  
>  out:

The less the string visitors are used, the happier I am.