Re: [Qemu-devel] [PATCH COLO-Frame v9 08/32] COLO/migration: establish a new communication path from destination to source

[zhanghailiang <zhang.zhanghailiang@huawei.com>]

On 2015/10/19 17:54, Dr. David Alan Gilbert wrote:
> * zhanghailiang (zhang.zhanghailiang@huawei.com) wrote:
>> Add a new member 'to_src_file' to MigrationIncomingState and a
>> new member 'from_dst_file' to MigrationState.
>> They will be used for returning messages from destination to source.
>> It will also be used by post-copy migration.
>>
>> Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
>> Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
>> Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
>> ---
>>   include/migration/migration.h |  3 ++-
>>   migration/colo.c              | 43 +++++++++++++++++++++++++++++++++++++++++++
>>   2 files changed, 45 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/migration/migration.h b/include/migration/migration.h
>> index 6488e03..0c94103 100644
>> --- a/include/migration/migration.h
>> +++ b/include/migration/migration.h
>> @@ -50,7 +50,7 @@ typedef QLIST_HEAD(, LoadStateEntry) LoadStateEntry_Head;
>>   /* State for the incoming migration */
>>   struct MigrationIncomingState {
>>       QEMUFile *from_src_file;
>> -
>> +    QEMUFile *to_src_file;
>>       int state;
>>
>>       bool have_colo_incoming_thread;
>> @@ -74,6 +74,7 @@ struct MigrationState
>>       QemuThread thread;
>>       QEMUBH *cleanup_bh;
>>       QEMUFile *to_dst_file;
>> +    QEMUFile  *from_dst_file;
>>       int parameters[MIGRATION_PARAMETER_MAX];
>>
>>       int state;
>> diff --git a/migration/colo.c b/migration/colo.c
>> index a341eee..5f4fb20 100644
>> --- a/migration/colo.c
>> +++ b/migration/colo.c
>> @@ -39,6 +39,20 @@ bool migration_incoming_in_colo_state(void)
>>   static void *colo_thread(void *opaque)
>>   {
>>       MigrationState *s = opaque;
>> +    int fd, ret = 0;
>> +
>> +    /* Dup the fd of to_dst_file */
>> +    fd = dup(qemu_get_fd(s->to_dst_file));
>> +    if (fd == -1) {
>> +        ret = -errno;
>> +        goto out;
>> +    }
>> +    s->from_dst_file = qemu_fopen_socket(fd, "rb");
>
> In my postcopy code I add the return-path opening as a new
> method on QEMUFile, that way if we get a return path working
> on another transport (RDMA which I hope to do) then it
> works;  have a look at 'Return path: Open a return path on QEMUFile for sockets'
>

I have looked at it. That's a good solution, we use the same fd for return path, and
i don't have to call qemu_file_shutdown two times in failover process.

>> +    if (!s->from_dst_file) {
>> +        ret = -EINVAL;
>> +        error_report("Open QEMUFile failed!");
>
> In errors, try to give detail of where a problem was;
> e.g. 'colo_thread: Open QEMUFile from_dst failed'.
>

OK. I will fix it in next version.

>> +        goto out;
>> +    }
>>
>>       qemu_mutex_lock_iothread();
>>       vm_start();
>> @@ -47,9 +61,17 @@ static void *colo_thread(void *opaque)
>>
>>       /*TODO: COLO checkpoint savevm loop*/
>>
>> +out:
>> +    if (ret < 0) {
>> +        error_report("Detect some error: %s", strerror(-ret));
>> +    }
>
> Again, best to say where the error happened.
>

Hmm, it is a little difficult to say where exactly this error happened here,
what i can do is to error out in the place where the error happened.
Here is only a summary for the error.

>
>>       migrate_set_state(&s->state, MIGRATION_STATUS_COLO,
>>                         MIGRATION_STATUS_COMPLETED);
>>
>> +    if (s->from_dst_file) {
>> +        qemu_fclose(s->from_dst_file);
>> +    }
>> +
>>       qemu_mutex_lock_iothread();
>>       qemu_bh_schedule(s->cleanup_bh);
>>       qemu_mutex_unlock_iothread();
>> @@ -86,12 +108,33 @@ void colo_init_checkpointer(MigrationState *s)
>>   void *colo_process_incoming_thread(void *opaque)
>>   {
>>       MigrationIncomingState *mis = opaque;
>> +    int fd, ret = 0;
>>
>>       migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE,
>>                         MIGRATION_STATUS_COLO);
>>
>> +    fd = dup(qemu_get_fd(mis->from_src_file));
>> +    if (fd < 0) {
>> +        ret = -errno;
>> +        goto out;
>> +    }
>> +    mis->to_src_file = qemu_fopen_socket(fd, "wb");
>> +    if (!mis->to_src_file) {
>> +        ret = -EINVAL;
>> +        error_report("Can't open incoming channel!");
>> +        goto out;
>> +    }
>
> Same as above.

OK. Will fix it.

Thanks,
zhanghailiang
>
>>       /* TODO: COLO checkpoint restore loop */
>>
>> +out:
>> +    if (ret < 0) {
>
>> +        error_report("colo incoming thread will exit, detect error: %s",
>> +                     strerror(-ret));
>> +    }
>> +
>> +    if (mis->to_src_file) {
>> +        qemu_fclose(mis->to_src_file);
>> +    }
>>       migration_incoming_exit_colo();
>>
>>       return NULL;
>> --
>> 1.8.3.1
>>
>>
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>
> .
>