Re: [Qemu-devel] [PATCH v9 04/12] migration: Start of multiple fd work

[Juan Quintela <quintela@redhat.com>]

"Daniel P. Berrange" <berrange@redhat.com> wrote:
> On Wed, Oct 04, 2017 at 12:46:28PM +0200, Juan Quintela wrote:
>> We create new channels for each new thread created. We send through
>> them a string containing <uuid> multifd <channel number> so we are
>> sure that we connect the right channels in both sides.
>
> This message needs updating now that we send a struct.
>
>
>> diff --git a/migration/ram.c b/migration/ram.c
>> index b83f8977c5..b57006594b 100644
>> --- a/migration/ram.c
>> +++ b/migration/ram.c
>> @@ -414,9 +425,27 @@ int multifd_save_cleanup(Error **errp)
>>      return ret;
>>  }
>>  
>> +typedef struct {
>> +    uint32_t version;
>> +    uint8_t id;
>> +    char uuid[UUID_FMT_LEN];
>> +} MigrateMultiFDInit_t;
>
> We add an __attribute__((packed)) here since we send it directly
> on the wire. Perhaps put 'uuid' field before 'id' when doing that
> so 'uuid' gets a more natural alignment.

ok.

> If we use 'unsigned char uuid[16]' then you don't need to convert
> from string format either...

I was looking at the "exported" commands in uuid.h, but I can use the
memcopy without problem.  Just feel like using a "detail" of the
implementation.



>
>>  static void *multifd_send_thread(void *opaque)
>>  {
>>      MultiFDSendParams *p = opaque;
>> +    MigrateMultiFDInit_t msg;
>> +    Error *local_err = NULL;
>> +    size_t ret;
>> +
>> +    msg.version = 1;
>> +    msg.id = p->id;
>> +    qemu_uuid_unparse(&qemu_uuid, (char *)&msg.uuid);
>
> eg this could be   memcpy(msg.uuid, qemu_uuid.data, sizeof(msg.uuid))
>
>> +    ret = qio_channel_write_all(p->c, (char *)&msg, sizeof(msg), &local_err);
>> +    if (ret != 0) {
>> +        terminate_multifd_send_threads(local_err);
>> +        return NULL;
>> +    }
>>  
>>      while (true) {
>>          qemu_mutex_lock(&p->mutex);
>> @@ -431,6 +460,27 @@ static void *multifd_send_thread(void *opaque)
>>      return NULL;
>>  }
>
>> +void multifd_new_channel(QIOChannel *ioc)
>> +{
>> +    MultiFDRecvParams *p;
>> +    MigrateMultiFDInit_t msg;
>> +    Error *local_err = NULL;
>> +    char *uuid;
>> +    size_t ret;
>> +
>> +    ret = qio_channel_read_all(ioc, (char *)&msg, sizeof(msg), &local_err);
>> +    if (ret != 0) {
>> +        terminate_multifd_recv_threads(local_err);
>> +        return;
>> +    }
>> +
>> +    uuid = qemu_uuid_unparse_strdup(&qemu_uuid);
>
> ...and here we would avoid need to unparse, instead..
>
>> +
>> +    if (strcmp(msg.uuid, uuid)) {
>
>   memcmp(msg.uuid, qemu_uuid.data, sizeof(msg.uuid) != 0
>
>> +        g_free(uuid);
>> +        error_setg(&local_err, "multifd: received uuid '%s' and expected "
>> +                   "uuid '%s' for channel %hhd", msg.uuid, uuid, msg.id);
>> +        terminate_multifd_recv_threads(local_err);
>> +        return;
>> +    }
>> +    g_free(uuid);

Thanks, Juan.