Re: [Qemu-devel] [PATCH COLO-Frame v13 10/39] COLO: Implement colo checkpoint protocol

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

On 2016/1/29 21:08, Dr. David Alan Gilbert wrote:
> * zhanghailiang (zhang.zhanghailiang@huawei.com) wrote:
>> We need communications protocol of user-defined to control the checkpoint
>> process.
>>
>> The new checkpoint request is started by Primary VM, and the interactive process
>> like below:
>> Checkpoint synchronizing points:
>>
>>                     Primary               Secondary
>>                                              initial work
>> 'checkpoint-ready'    <-------------------- @
>>
>> 'checkpoint-request'  @ -------------------->
>>                                              Suspend (Only in hybrid mode)
>> 'checkpoint-reply'    <-------------------- @
>>                        Suspend&Save state
>> 'vmstate-send'        @ -------------------->
>>                        Send state            Receive state
>> 'vmstate-received'    <-------------------- @
>>                        Release packets       Load state
>> 'vmstate-load'        <-------------------- @
>>                        Resume                Resume (Only in hybrid mode)
>>
>>                        Start Comparing (Only in hybrid mode)
>> NOTE:
>>   1) '@' who sends the message
>>   2) Every sync-point is synchronized by two sides with only
>>      one handshake(single direction) for low-latency.
>>      If more strict synchronization is required, a opposite direction
>>      sync-point should be added.
>>   3) Since sync-points are single direction, the remote side may
>>      go forward a lot when this side just receives the sync-point.
>>   4) For now, we only support 'periodic' checkpoint, for which
>>     the Secondary VM is not running, later we will support 'hybrid' mode.
>>
>> Signed-off-by: zhanghailiang <zhang.zhanghailiang@huawei.com>
>> Signed-off-by: Li Zhijian <lizhijian@cn.fujitsu.com>
>> Signed-off-by: Gonglei <arei.gonglei@huawei.com>
>> Cc: Eric Blake <eblake@redhat.com>
>> Cc: Markus Armbruster <armbru@redhat.com>
>> Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
>> ---
>> v13:
>> - Refactor colo command related helper functions, use 'Error **errp' parameter
>>    instead of return value to indicate success or failure.
>> - Fix some other comments from Markus.
>>
>> v12:
>> - Rename colo_ctl_put() to colo_put_cmd()
>> - Rename colo_ctl_get() to colo_get_check_cmd() and drop
>>    the third parameter
>> - Rename colo_ctl_get_cmd() to colo_get_cmd()
>> - Remove useless 'invalid' member for COLOcommand enum.
>> v11:
>> - Add missing 'checkpoint-ready' communication in comment.
>> - Use parameter to return 'value' for colo_ctl_get() (Dave's suggestion)
>> - Fix trace for colo_ctl_get() to trace command and value both
>> v10:
>> - Rename enum COLOCmd to COLOCommand (Eric's suggestion).
>> - Remove unused 'ram-steal'
>> ---
>>   migration/colo.c | 201 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>>   qapi-schema.json |  25 +++++++
>>   trace-events     |   2 +
>>   3 files changed, 226 insertions(+), 2 deletions(-)
>>
>> diff --git a/migration/colo.c b/migration/colo.c
>> index 65ac0c9..c76e1fa 100644
>> --- a/migration/colo.c
>> +++ b/migration/colo.c
>> @@ -10,6 +10,7 @@
>>    * later.  See the COPYING file in the top-level directory.
>>    */
>>
>> +#include <unistd.h>
>>   #include "sysemu/sysemu.h"
>>   #include "migration/colo.h"
>>   #include "trace.h"
>> @@ -34,22 +35,147 @@ bool migration_incoming_in_colo_state(void)
>>       return mis && (mis->state == MIGRATION_STATUS_COLO);
>>   }
>>
>> +static void colo_put_cmd(QEMUFile *f, COLOCommand cmd,
>> +                         Error **errp)
>> +{
>> +    int ret;
>> +
>> +    if (cmd >= COLO_COMMAND__MAX) {
>> +        error_setg(errp, "%s: Invalid cmd", __func__);
>> +        return;
>> +    }
>> +    qemu_put_be32(f, cmd);
>> +    qemu_fflush(f);
>> +
>> +    ret = qemu_file_get_error(f);
>> +    if (ret < 0) {
>> +        error_setg_errno(errp, -ret, "Can't put COLO command");
>> +    }
>> +    trace_colo_put_cmd(COLOCommand_lookup[cmd]);
>> +}
>> +
>> +static COLOCommand colo_get_cmd(QEMUFile *f, Error **errp)
>> +{
>> +    COLOCommand cmd;
>> +    int ret;
>> +
>> +    cmd = qemu_get_be32(f);
>> +    ret = qemu_file_get_error(f);
>> +    if (ret < 0) {
>> +        error_setg_errno(errp, -ret, "Can't get COLO command");
>> +        return cmd;
>> +    }
>> +    if (cmd >= COLO_COMMAND__MAX) {
>
> I'm not sure this is guaranteed to do the right thing if the value
> read was negative and converted to the enum;  it seems to depend
> a bit on the compiler as to whether an enum is signed or not;
> but it seems the normal behaviour is for the enum to be unsigned

Interesting question, we can define a negative enumeration-constant,
enum test {
     TEST_A = -2,
     TEST_B = 0,
} value;
So i suppose an enum is signed, and ISO C standard (c99 6.4.4.3) states that
the enumeration constants are of type int.
But it seems that gcc does not follow this standard strictly,
i got the exact answer from its specification:
https://gcc.gnu.org/onlinedocs/gcc/Structures-unions-enumerations-and-bit-fields-implementation.html#Structures-unions-enumerations-and-bit-fields-implementation
"Normally, the type is unsigned int if there are no negative values in the enumeration, otherwise int."

> as long as there are no negative values when it's declared; so it looks
> safe in practice.
>
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
>

Thanks,
Hailiang

>> +        error_setg(errp, "%s: Invalid cmd", __func__);
>> +        return cmd;
>> +    }
>> +    trace_colo_get_cmd(COLOCommand_lookup[cmd]);
>> +    return cmd;
>> +}
>> +
>> +static void colo_get_check_cmd(QEMUFile *f, COLOCommand expect_cmd,
>> +                               Error **errp)
>> +{
>> +    COLOCommand cmd;
>> +    Error *local_err = NULL;
>> +
>> +    cmd = colo_get_cmd(f, &local_err);
>> +    if (local_err) {
>> +        error_propagate(errp, local_err);
>> +        return;
>> +    }
>> +    if (cmd != expect_cmd) {
>> +        error_setg(errp, "Unexpected COLO command %d, expected %d",
>> +                          expect_cmd, cmd);
>> +    }
>> +}
>> +
>> +static int colo_do_checkpoint_transaction(MigrationState *s)
>> +{
>> +    Error *local_err = NULL;
>> +
>> +    colo_put_cmd(s->to_dst_file, COLO_COMMAND_CHECKPOINT_REQUEST,
>> +                 &local_err);
>> +    if (local_err) {
>> +        goto out;
>> +    }
>> +
>> +    colo_get_check_cmd(s->rp_state.from_dst_file,
>> +                       COLO_COMMAND_CHECKPOINT_REPLY, &local_err);
>> +    if (local_err) {
>> +        goto out;
>> +    }
>> +
>> +    /* TODO: suspend and save vm state to colo buffer */
>> +
>> +    colo_put_cmd(s->to_dst_file, COLO_COMMAND_VMSTATE_SEND, &local_err);
>> +    if (local_err) {
>> +        goto out;
>> +    }
>> +
>> +    /* TODO: send vmstate to Secondary */
>> +
>> +    colo_get_check_cmd(s->rp_state.from_dst_file,
>> +                       COLO_COMMAND_VMSTATE_RECEIVED, &local_err);
>> +    if (local_err) {
>> +        goto out;
>> +    }
>> +
>> +    colo_get_check_cmd(s->rp_state.from_dst_file,
>> +                       COLO_COMMAND_VMSTATE_LOADED, &local_err);
>> +    if (local_err) {
>> +        goto out;
>> +    }
>> +
>> +    /* TODO: resume Primary */
>> +
>> +    return 0;
>> +out:
>> +    if (local_err) {
>> +        error_report_err(local_err);
>> +    }
>> +    return -EINVAL;
>> +}
>> +
>>   static void colo_process_checkpoint(MigrationState *s)
>>   {
>> +    Error *local_err = NULL;
>> +    int ret;
>> +
>>       s->rp_state.from_dst_file = qemu_file_get_return_path(s->to_dst_file);
>>       if (!s->rp_state.from_dst_file) {
>>           error_report("Open QEMUFile from_dst_file failed");
>>           goto out;
>>       }
>>
>> +    /*
>> +     * Wait for Secondary finish loading vm states and enter COLO
>> +     * restore.
>> +     */
>> +    colo_get_check_cmd(s->rp_state.from_dst_file,
>> +                       COLO_COMMAND_CHECKPOINT_READY, &local_err);
>> +    if (local_err) {
>> +        goto out;
>> +    }
>> +
>>       qemu_mutex_lock_iothread();
>>       vm_start();
>>       qemu_mutex_unlock_iothread();
>>       trace_colo_vm_state_change("stop", "run");
>>
>> -    /*TODO: COLO checkpoint savevm loop*/
>> +    while (s->state == MIGRATION_STATUS_COLO) {
>> +        /* start a colo checkpoint */
>> +        ret = colo_do_checkpoint_transaction(s);
>> +        if (ret < 0) {
>> +            goto out;
>> +        }
>> +    }
>>
>>   out:
>> +    /* Throw the unreported error message after exited from loop */
>> +    if (local_err) {
>> +        error_report_err(local_err);
>> +    }
>>       migrate_set_state(&s->state, MIGRATION_STATUS_COLO,
>>                         MIGRATION_STATUS_COMPLETED);
>>
>> @@ -67,9 +193,33 @@ void migrate_start_colo_process(MigrationState *s)
>>       qemu_mutex_lock_iothread();
>>   }
>>
>> +static void colo_wait_handle_cmd(QEMUFile *f, int *checkpoint_request,
>> +                                 Error **errp)
>> +{
>> +    COLOCommand cmd;
>> +    Error *local_err = NULL;
>> +
>> +    cmd = colo_get_cmd(f, &local_err);
>> +    if (local_err) {
>> +        error_propagate(errp, local_err);
>> +        return;
>> +    }
>> +
>> +    switch (cmd) {
>> +    case COLO_COMMAND_CHECKPOINT_REQUEST:
>> +        *checkpoint_request = 1;
>> +        break;
>> +    default:
>> +        *checkpoint_request = 0;
>> +        error_setg(errp, "Got unknown COLO command: %d", cmd);
>> +        break;
>> +    }
>> +}
>> +
>>   void *colo_process_incoming_thread(void *opaque)
>>   {
>>       MigrationIncomingState *mis = opaque;
>> +    Error *local_err = NULL;
>>
>>       migrate_set_state(&mis->state, MIGRATION_STATUS_ACTIVE,
>>                         MIGRATION_STATUS_COLO);
>> @@ -85,9 +235,56 @@ void *colo_process_incoming_thread(void *opaque)
>>       */
>>       qemu_file_set_blocking(mis->from_src_file, true);
>>
>> -    /* TODO: COLO checkpoint restore loop */
>> +    colo_put_cmd(mis->to_src_file, COLO_COMMAND_CHECKPOINT_READY,
>> +                 &local_err);
>> +    if (local_err) {
>> +        goto out;
>> +    }
>> +
>> +    while (mis->state == MIGRATION_STATUS_COLO) {
>> +        int request;
>> +
>> +        colo_wait_handle_cmd(mis->from_src_file, &request, &local_err);
>> +        if (local_err) {
>> +            goto out;
>> +        }
>> +        assert(request);
>> +        /* FIXME: This is unnecessary for periodic checkpoint mode */
>> +        colo_put_cmd(mis->to_src_file, COLO_COMMAND_CHECKPOINT_REPLY,
>> +                     &local_err);
>> +        if (local_err) {
>> +            goto out;
>> +        }
>> +
>> +        colo_get_check_cmd(mis->from_src_file,
>> +                           COLO_COMMAND_VMSTATE_SEND, &local_err);
>> +        if (local_err) {
>> +            goto out;
>> +        }
>> +
>> +        /* TODO: read migration data into colo buffer */
>> +
>> +        colo_put_cmd(mis->to_src_file, COLO_COMMAND_VMSTATE_RECEIVED,
>> +                     &local_err);
>> +        if (local_err) {
>> +            goto out;
>> +        }
>> +
>> +        /* TODO: load vm state */
>> +
>> +        colo_put_cmd(mis->to_src_file, COLO_COMMAND_VMSTATE_LOADED,
>> +                     &local_err);
>> +        if (local_err) {
>> +            goto out;
>> +        }
>> +    }
>>
>>   out:
>> +    /* Throw the unreported error message after exited from loop */
>> +    if (local_err) {
>> +        error_report_err(local_err);
>> +    }
>> +
>>       if (mis->to_src_file) {
>>           qemu_fclose(mis->to_src_file);
>>       }
>> diff --git a/qapi-schema.json b/qapi-schema.json
>> index 6eefad2..4ea4108 100644
>> --- a/qapi-schema.json
>> +++ b/qapi-schema.json
>> @@ -718,6 +718,31 @@
>>   { 'command': 'migrate-start-postcopy' }
>>
>>   ##
>> +# @COLOCommand
>> +#
>> +# The commands for COLO fault tolerance
>> +#
>> +# @checkpoint-ready: SVM is ready for checkpointing
>> +#
>> +# @checkpoint-request: PVM tells SVM to prepare for new checkpointing
>> +#
>> +# @checkpoint-reply: SVM gets PVM's checkpoint request
>> +#
>> +# @vmstate-send: VM's state will be sent by PVM.
>> +#
>> +# @vmstate-size: The total size of VMstate.
>> +#
>> +# @vmstate-received: VM's state has been received by SVM.
>> +#
>> +# @vmstate-loaded: VM's state has been loaded by SVM.
>> +#
>> +# Since: 2.6
>> +##
>> +{ 'enum': 'COLOCommand',
>> +  'data': [ 'checkpoint-ready', 'checkpoint-request', 'checkpoint-reply',
>> +            'vmstate-send', 'vmstate-size', 'vmstate-received',
>> +            'vmstate-loaded' ] }
>> +
>>   # @MouseInfo:
>>   #
>>   # Information about a mouse device.
>> diff --git a/trace-events b/trace-events
>> index 57ddc8f..51b2305 100644
>> --- a/trace-events
>> +++ b/trace-events
>> @@ -1581,6 +1581,8 @@ postcopy_ram_incoming_cleanup_join(void) ""
>>
>>   # migration/colo.c
>>   colo_vm_state_change(const char *old, const char *new) "Change '%s' => '%s'"
>> +colo_put_cmd(const char *msg) "Send '%s' cmd"
>> +colo_get_cmd(const char *msg) "Receive '%s' cmd"
>>
>>   # kvm-all.c
>>   kvm_ioctl(int type, void *arg) "type 0x%x, arg %p"
>> --
>> 1.8.3.1
>>
>>
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
>
> .
>