From: Anthony Liguori <aliguori@us.ibm.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: aliguori@linux.vnet.ibm.com,
Michael Roth <mdroth@linux.vnet.ibm.com>,
qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [RFC] New Migration Protocol using Visitor Interface
Date: Mon, 03 Oct 2011 09:42:02 -0500 [thread overview]
Message-ID: <4E89C9BA.8070404@us.ibm.com> (raw)
In-Reply-To: <20111003141140.GB19689@redhat.com>
On 10/03/2011 09:11 AM, Michael S. Tsirkin wrote:
> On Mon, Oct 03, 2011 at 08:43:54AM -0500, Anthony Liguori wrote:
>>>> visit_start_array(v, "entries", errp);
>>>> for (int i = 0; i< s->size; i++) {
>>>> visit_type_int(v, NULL,&s->entry[i], errp);
>>>> }
>>>> visit_end_array(v, errp);
>>>
>>> Sequences can encode structures not just arrays.
>>> How would you encode this for example:
>>>
>>> SEQUENCE OF { VQN: INTEGER, SEQUENCE { OPTIONAL VECTOR: INTEGER} }
>>
>> visit_start_array(v, "vqs", errp);
>> for (i = 0; i< s->n_vqs; i++) {
>> // Array elements never have a name, hence NULL name
>> visit_start_struct(v, "VirtQueue", NULL, errp);
>> visit_type_int(v,&s->vq[i].num, "vqn", errp);
>>
>> // Given this sub-struct an arbitrary name. It could also be anonymous.
>> visit_start_struct(v, "MsixInfo", "msix_info", errp);
>> if (s->vq[i].msix_enabled) {
>> visit_type_int(v,&s->vq[i].vector, "vector", errp);
>
> Why is this a pointer to vector, btw?
So you can write a single visit function that works for input or output.
Think of the simple case like:
void visit_simple_type(Visitor *v, SimpleType *t, const char *name, Error **errp)
{
visit_start_struct(v, "SimpleType", name, errp);
visit_type_int(v, &t->a, "a", errp);
visit_type_int(v, &t->b, "b", errp);
visit_end_struct(v, errp);
}
For complex types like Virtio, you need to do a bit more. You wouldn't do a
simple for () {} loop but instead use the Visitor list mechanism. That would
eliminate the need to have to marshal n_vqs.
>
>> }
>> visit_end_struct(v, errp);
>>
>> visit_end_struct(v, errp);
>> }
>> visit_end_array(v, errp);
>>
>> This would also generate JSON of:
>>
>> 'vqs': [ { 'vqn': 2, 'msix_info': { 'vector': 3 } } ]
>
> How would optional fields be handled?
As far as the Visitor goes, if something is optional you just don't encode it.
If you need to key off the presence of a field, presumably you could just check
to see whether it succeeded or failed to visit that field. I'm not 100% sure if
you can do a single input/output visitor when you have optional fields.
My rough thinking is that each device would have a input/output visitor callback
that took the same signature. That gives the flexibility of having two separate
interfaces but in the common case, you just pass the same function for both.
> Specifically
> the case where first field in a sequence tells
> you the meaning of the following ones?
Can you give me the example in ASN.1?
Regards,
Anthony Liguori
next prev parent reply other threads:[~2011-10-03 14:42 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-19 14:41 [Qemu-devel] [RFC] New Migration Protocol using Visitor Interface Michael Roth
2011-09-19 14:41 ` [Qemu-devel] [RFC 1/8] qapi: add Visitor interfaces for uint*_t and int*_t Michael Roth
2011-09-19 14:41 ` [Qemu-devel] [RFC 2/8] qapi: add QemuFileOutputVisitor Michael Roth
2011-09-19 14:41 ` [Qemu-devel] [RFC 3/8] qapi: add QemuFileInputVisitor Michael Roth
2011-10-24 23:59 ` Chris Krumme
2011-09-19 14:41 ` [Qemu-devel] [RFC 4/8] savevm: move QEMUFile interfaces into qemu-file.c Michael Roth
2011-09-24 7:23 ` Blue Swirl
2011-09-19 14:41 ` [Qemu-devel] [RFC 5/8] qapi: test cases for QEMUFile input/output visitors Michael Roth
2011-09-19 14:41 ` [Qemu-devel] [RFC 6/8] savevm: add QEMUFile->visitor lookup routines Michael Roth
2011-09-19 14:41 ` [Qemu-devel] [RFC 7/8] cutil: add strocat(), to concat a string to an offset in another Michael Roth
2011-09-20 10:43 ` Paolo Bonzini
2011-09-19 14:41 ` [Qemu-devel] [RFC 8/8] slirp: convert save/load function to visitor interface Michael Roth
2011-09-30 13:39 ` Anthony Liguori
2011-09-30 14:08 ` Michael Roth
2011-10-02 20:21 ` [Qemu-devel] [RFC] New Migration Protocol using Visitor Interface Stefan Berger
2011-10-02 21:08 ` Michael S. Tsirkin
2011-10-03 12:55 ` Anthony Liguori
2011-10-03 13:10 ` Stefan Berger
2011-10-03 13:18 ` Anthony Liguori
2011-10-03 13:30 ` Michael S. Tsirkin
2011-10-03 13:48 ` Anthony Liguori
2011-10-03 14:18 ` Michael S. Tsirkin
2011-10-03 14:56 ` Anthony Liguori
2011-10-03 15:42 ` Michael S. Tsirkin
2011-10-03 13:38 ` Michael S. Tsirkin
2011-10-03 13:51 ` Anthony Liguori
2011-10-03 14:41 ` Michael S. Tsirkin
2011-10-03 15:00 ` Anthony Liguori
2011-10-03 15:45 ` Michael S. Tsirkin
2011-10-03 16:05 ` Anthony Liguori
2011-10-03 16:24 ` Daniel P. Berrange
2011-10-03 16:51 ` Michael S. Tsirkin
2011-10-05 11:28 ` Michael S. Tsirkin
2011-10-05 12:46 ` Anthony Liguori
2011-10-03 6:46 ` Michael S. Tsirkin
2011-10-03 12:51 ` Anthony Liguori
2011-10-03 13:24 ` Michael S. Tsirkin
2011-10-03 13:43 ` Anthony Liguori
2011-10-03 14:11 ` Michael S. Tsirkin
2011-10-03 14:42 ` Anthony Liguori [this message]
2011-10-03 15:29 ` Michael S. Tsirkin
2011-10-03 15:44 ` Anthony Liguori
2011-10-03 15:58 ` Michael S. Tsirkin
2011-10-03 16:02 ` Anthony Liguori
2011-10-03 14:15 ` Michael S. Tsirkin
2011-10-03 14:55 ` Anthony Liguori
2011-10-03 15:41 ` Michael S. Tsirkin
2011-10-05 2:05 ` Stefan Berger
2011-10-05 12:54 ` Anthony Liguori
2011-10-05 19:06 ` Michael S. Tsirkin
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