[v6,11/25] replay: implement replay-seek command to proceed to the desired step

This patch adds hmp/qmp commands replay_seek/replay-seek that proceed
the execution to the specified step.
The commands automatically loads nearest snapshot and replay the execution
to find the desired step.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>

--

v2:
 - renamed replay_seek qmp command into replay-seek
   (suggested by Eric Blake)
---
 hmp-commands.hx           |   15 ++++++++
 hmp.h                     |    1 +
 qapi/misc.json            |   16 ++++++++
 replay/replay-debugging.c |   89 +++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 121 insertions(+)

Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru> writes:

> This patch adds hmp/qmp commands replay_seek/replay-seek that proceed
> the execution to the specified step.
> The commands automatically loads nearest snapshot and replay the execution
> to find the desired step.
>
> Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgaluk@ispras.ru>
>
> --
>
> v2:
>  - renamed replay_seek qmp command into replay-seek
>    (suggested by Eric Blake)
> ---
>  hmp-commands.hx           |   15 ++++++++
>  hmp.h                     |    1 +
>  qapi/misc.json            |   16 ++++++++
>  replay/replay-debugging.c |   89 +++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 121 insertions(+)
>
> diff --git a/hmp-commands.hx b/hmp-commands.hx
> index aa0794e..8d4065b 100644
> --- a/hmp-commands.hx
> +++ b/hmp-commands.hx
> @@ -1903,6 +1903,21 @@ Execution stops when the specified step is reached.
>  ETEXI
>  
>      {
> +        .name       = "replay_seek",
> +        .args_type  = "step:i",
> +        .params     = "step",
> +        .help       = "rewinds replay to the specified step",
> +        .cmd        = hmp_replay_seek,
> +    },
> +
> +STEXI
> +@item replay_seek @var{step}
> +@findex replay_seek
> +Automatically proceeds to the specified step, when replaying
> +the execution.

Drop the comma (I think).

> +ETEXI
> +
> +    {
>          .name       = "info",
>          .args_type  = "item:s?",
>          .params     = "[subcommand]",
> diff --git a/hmp.h b/hmp.h
> index ad94abe..a7d3bce 100644
> --- a/hmp.h
> +++ b/hmp.h
> @@ -150,5 +150,6 @@ void hmp_info_memory_size_summary(Monitor *mon, const QDict *qdict);
>  void hmp_info_sev(Monitor *mon, const QDict *qdict);
>  void hmp_info_replay(Monitor *mon, const QDict *qdict);
>  void hmp_replay_break(Monitor *mon, const QDict *qdict);
> +void hmp_replay_seek(Monitor *mon, const QDict *qdict);
>  
>  #endif
> diff --git a/qapi/misc.json b/qapi/misc.json
> index 4fcd211..7389cc6 100644
> --- a/qapi/misc.json
> +++ b/qapi/misc.json
> @@ -3152,6 +3152,22 @@
>  { 'command': 'replay-break', 'data': { 'step': 'int' } }
>  
>  ##
> +# @replay-seek:
> +#
> +# Automatically proceeds to the specified step, when replaying
> +# the execution.
> +#
> +# @step: destination execution step
> +#
> +# Since: 3.1
> +#
> +# Example:
> +#
> +# -> { "execute": "replay-seek", "data": { "step": 220414 } }
> +##
> +{ 'command': 'replay-seek', 'data': { 'step': 'int' } }
> +
> +##
>  # @xen-load-devices-state:
>  #
>  # Load the state of all devices from file. The RAM and the block devices
> diff --git a/replay/replay-debugging.c b/replay/replay-debugging.c
> index c6b80c0..e605ee0 100644
> --- a/replay/replay-debugging.c
> +++ b/replay/replay-debugging.c
> @@ -18,6 +18,8 @@
>  #include "qapi/qapi-commands-misc.h"
>  #include "qapi/qmp/qdict.h"
>  #include "qemu/timer.h"
> +#include "block/snapshot.h"
> +#include "migration/snapshot.h"
>  
>  void hmp_info_replay(Monitor *mon, const QDict *qdict)
>  {
> @@ -94,3 +96,90 @@ void hmp_replay_break(Monitor *mon, const QDict *qdict)
>          return;
>      }
>  }
> +
> +static char *replay_find_nearest_snapshot(int64_t step, int64_t* snapshot_step)
> +{
> +    BlockDriverState *bs;
> +    QEMUSnapshotInfo *sn_tab;
> +    QEMUSnapshotInfo *nearest = NULL;
> +    char *ret = NULL;
> +    int nb_sns, i;
> +    AioContext *aio_context;
> +
> +    *snapshot_step = -1;
> +
> +    bs = bdrv_all_find_vmstate_bs();
> +    if (!bs) {
> +        goto fail;
> +    }
> +    aio_context = bdrv_get_aio_context(bs);
> +
> +    aio_context_acquire(aio_context);
> +    nb_sns = bdrv_snapshot_list(bs, &sn_tab);
> +    aio_context_release(aio_context);
> +
> +    for (i = 0; i < nb_sns; i++) {
> +        if (bdrv_all_find_snapshot(sn_tab[i].name, &bs) == 0) {
> +            if (sn_tab[i].icount != -1ULL
> +                && sn_tab[i].icount <= step
> +                && (!nearest || nearest->icount < sn_tab[i].icount)) {
> +                nearest = &sn_tab[i];
> +            }
> +        }
> +    }
> +    if (nearest) {
> +        ret = g_strdup(nearest->name);
> +        *snapshot_step = nearest->icount;
> +    }
> +    g_free(sn_tab);
> +
> +fail:
> +    return ret;
> +}
> +
> +static void replay_seek(int64_t step, Error **errp, QEMUTimerCB callback)

By convention, Error **errp goes last.

> +{
> +    char *snapshot = NULL;

Suggest blank line between declaration and statement.

> +    if (replay_mode != REPLAY_MODE_PLAY) {
> +        error_setg(errp, "replay must be enabled to seek");
> +        return;
> +    }
> +    if (!replay_snapshot) {
> +        error_setg(errp, "snapshotting is disabled");
> +        return;
> +    }
> +    int64_t snapshot_step = -1;

Dead initialization.

Recommend to declare this variable at the beginning of the function.

> +    snapshot = replay_find_nearest_snapshot(step, &snapshot_step);
> +    if (snapshot) {
> +        if (step < replay_get_current_step()
> +            || replay_get_current_step() < snapshot_step) {
> +            vm_stop(RUN_STATE_RESTORE_VM);
> +            load_snapshot(snapshot, errp);
> +        }
> +        g_free(snapshot);
> +    }
> +    if (replay_get_current_step() <= step) {
> +        replay_break(step, callback, NULL);
> +        vm_start();
> +    } else {
> +        error_setg(errp, "cannot seek to the specified step");
> +    }
> +}
> +
> +void qmp_replay_seek(int64_t step, Error **errp)
> +{
> +    replay_seek(step, errp, replay_stop_vm);
> +}
> +
> +void hmp_replay_seek(Monitor *mon, const QDict *qdict)
> +{
> +    int64_t step = qdict_get_try_int(qdict, "step", -1LL);
> +    Error *err = NULL;
> +
> +    qmp_replay_seek(step, &err);
> +    if (err) {
> +        monitor_printf(mon, "replay_seek error: %s\n", error_get_pretty(err));
> +        error_free(err);

Same as for the previous patch's hmp_replay_break():

           error_report_err(err);

> +        return;
> +    }
> +}