Re: [PATCH v5 08/13] migration/multifd: Add new migration option for multifd DSA offloading.

[Fabiano Rosas <farosas@suse.de>]

Yichen Wang <yichen.wang@bytedance.com> writes:

> On Thu, Jul 11, 2024 at 2:53 PM Yichen Wang <yichen.wang@bytedance.com> wrote:
>
>> diff --git a/migration/options.c b/migration/options.c
>> index 645f55003d..f839493016 100644
>> --- a/migration/options.c
>> +++ b/migration/options.c
>> @@ -29,6 +29,7 @@
>>  #include "ram.h"
>>  #include "options.h"
>>  #include "sysemu/kvm.h"
>> +#include <cpuid.h>
>>
>>  /* Maximum migrate downtime set to 2000 seconds */
>>  #define MAX_MIGRATE_DOWNTIME_SECONDS 2000
>> @@ -162,6 +163,10 @@ Property migration_properties[] = {
>>      DEFINE_PROP_ZERO_PAGE_DETECTION("zero-page-detection", MigrationState,
>>                         parameters.zero_page_detection,
>>                         ZERO_PAGE_DETECTION_MULTIFD),
>> +    /* DEFINE_PROP_ARRAY("dsa-accel-path", MigrationState, x, */
>> +    /*                    parameters.dsa_accel_path, qdev_prop_string, char *), */

This is mostly correct, I think, you just need to create a field in
MigrationState to keep the length (instead of x). However, I found out
just now that this only works with QMP. Let me ask for other's
opinions...

>> +    /* DEFINE_PROP_STRING("dsa-accel-path", MigrationState, */
>> +    /*                    parameters.dsa_accel_path), */
>>
>>      /* Migration capabilities */
>>      DEFINE_PROP_MIG_CAP("x-xbzrle", MIGRATION_CAPABILITY_XBZRLE),
>
> I changed the dsa-accel-path to be a ['str'], i.e. strList* in C.
> However, I am having a hard time about how to define the proper
> properties here. I don't know what MACRO to use and I can't find good
> examples... Need some guidance about how to proceed. Basically I will
> need this to pass something like '-global
> migration.dsa-accel-path="/dev/dsa/wq0.0"' in cmdline, or
> "migrate_set_parameter dsa-accel-path" in QEMU CLI. Don't know how to
> pass strList there.
>
> Thanks very much!

@Daniel, @Markus, any idea here?

If I'm reading this commit[1] right, it seems we decided to disallow
passing of arrays without JSON, which affects -global on the
command-line and HMP.

1- b06f8b500d (qdev: Rework array properties based on list visitor,
2023-11-09)

QMP shell:
(QEMU) migrate-set-parameters dsa-accel-path=['a','b']
{"return": {}}

HMP:
(qemu) migrate_set_parameter dsa-accel-path "['a','b']"
qemu-system-x86_64: ../qapi/string-input-visitor.c:343: parse_type_str:
Assertion `siv->lm == LM_NONE' failed.

Any recommendation? I believe all migration parameters so far can be set
via those means, I don't think we can allow only this one to be
QMP-only.

Or am I just missing something?