Re: [Qemu-devel] [PATCH v2 1/4] blockjob: Allow nested pause

[Paolo Bonzini <pbonzini@redhat.com>]

On 03/04/2015 16:05, Fam Zheng wrote:
> This patch changes block_job_pause to increase the pause counter and
> block_job_resume to decrease it.
> 
> The counter will allow calling block_job_pause/block_job_resume
> unconditionally on a job when we need to suspend the IO temporarily.
> 
> From now on, each block_job_resume must be paired with a block_job_pause
> to keep the counter balanced.
> 
> The user pause from QMP or HMP will only trigger block_job_pause once
> until it's resumed, this is achieved by adding a user_paused flag in
> BlockJob.
> 
> One occurrence of block_job_resume in mirror_complete is replaced with
> block_job_enter which does what is necessary.
> 
> In block_job_cancel, the cancel flag is good enough to instruct
> coroutines to quit loop, so use block_job_enter to replace the unpaired
> block_job_resume.
> 
> Upon block job IO error, user is notified about the entering to the
> pause state, so this pause belongs to user pause, set the flag
> accordingly and expect a matching QMP resume.
> 
> Signed-off-by: Fam Zheng <famz@redhat.com>
> ---
>  block/mirror.c           |  2 +-
>  blockdev.c               |  8 +++++---
>  blockjob.c               | 23 +++++++++++++++++------
>  include/block/blockjob.h | 20 ++++++++++++++++----
>  4 files changed, 39 insertions(+), 14 deletions(-)
> 
> diff --git a/block/mirror.c b/block/mirror.c
> index 4056164..65b1718 100644
> --- a/block/mirror.c
> +++ b/block/mirror.c
> @@ -634,7 +634,7 @@ static void mirror_complete(BlockJob *job, Error **errp)
>      }
>  
>      s->should_complete = true;
> -    block_job_resume(job);
> +    block_job_enter(&s->common);
>  }
>  
>  static const BlockJobDriver mirror_job_driver = {
> diff --git a/blockdev.c b/blockdev.c
> index fbb3a79..9132d69 100644
> --- a/blockdev.c
> +++ b/blockdev.c
> @@ -2699,7 +2699,7 @@ void qmp_block_job_cancel(const char *device,
>          force = false;
>      }
>  
> -    if (job->paused && !force) {
> +    if (job->user_paused && !force) {
>          error_setg(errp, "The block job for device '%s' is currently paused",
>                     device);
>          goto out;
> @@ -2716,10 +2716,11 @@ void qmp_block_job_pause(const char *device, Error **errp)
>      AioContext *aio_context;
>      BlockJob *job = find_block_job(device, &aio_context, errp);
>  
> -    if (!job) {
> +    if (!job || job->user_paused) {
>          return;
>      }
>  
> +    job->user_paused = true;
>      trace_qmp_block_job_pause(job);
>      block_job_pause(job);
>      aio_context_release(aio_context);
> @@ -2730,10 +2731,11 @@ void qmp_block_job_resume(const char *device, Error **errp)
>      AioContext *aio_context;
>      BlockJob *job = find_block_job(device, &aio_context, errp);
>  
> -    if (!job) {
> +    if (!job || !job->user_paused) {
>          return;
>      }
>  
> +    job->user_paused = false;
>      trace_qmp_block_job_resume(job);
>      block_job_resume(job);
>      aio_context_release(aio_context);
> diff --git a/blockjob.c b/blockjob.c
> index ba2255d..2755465 100644
> --- a/blockjob.c
> +++ b/blockjob.c
> @@ -107,7 +107,7 @@ void block_job_set_speed(BlockJob *job, int64_t speed, Error **errp)
>  
>  void block_job_complete(BlockJob *job, Error **errp)
>  {
> -    if (job->paused || job->cancelled || !job->driver->complete) {
> +    if (job->pause_count || job->cancelled || !job->driver->complete) {
>          error_set(errp, QERR_BLOCK_JOB_NOT_READY,
>                    bdrv_get_device_name(job->bs));
>          return;
> @@ -118,17 +118,26 @@ void block_job_complete(BlockJob *job, Error **errp)
>  
>  void block_job_pause(BlockJob *job)
>  {
> -    job->paused = true;
> +    job->pause_count++;
>  }
>  
>  bool block_job_is_paused(BlockJob *job)
>  {
> -    return job->paused;
> +    return job->pause_count > 0;
>  }
>  
>  void block_job_resume(BlockJob *job)
>  {
> -    job->paused = false;
> +    assert(job->pause_count > 0);
> +    job->pause_count--;
> +    if (job->pause_count) {
> +        return;
> +    }
> +    block_job_enter(job);
> +}
> +
> +void block_job_enter(BlockJob *job)
> +{
>      block_job_iostatus_reset(job);
>      if (job->co && !job->busy) {
>          qemu_coroutine_enter(job->co, NULL);
> @@ -138,7 +147,7 @@ void block_job_resume(BlockJob *job)
>  void block_job_cancel(BlockJob *job)
>  {
>      job->cancelled = true;
> -    block_job_resume(job);
> +    block_job_enter(job);
>  }
>  
>  bool block_job_is_cancelled(BlockJob *job)
> @@ -258,7 +267,7 @@ BlockJobInfo *block_job_query(BlockJob *job)
>      info->device    = g_strdup(bdrv_get_device_name(job->bs));
>      info->len       = job->len;
>      info->busy      = job->busy;
> -    info->paused    = job->paused;
> +    info->paused    = job->pause_count > 0;
>      info->offset    = job->offset;
>      info->speed     = job->speed;
>      info->io_status = job->iostatus;
> @@ -335,6 +344,8 @@ BlockErrorAction block_job_error_action(BlockJob *job, BlockDriverState *bs,
>                                      IO_OPERATION_TYPE_WRITE,
>                                      action, &error_abort);
>      if (action == BLOCK_ERROR_ACTION_STOP) {
> +        /* make the pause user visible, which will be resumed from QMP. */
> +        job->user_paused = true;
>          block_job_pause(job);
>          block_job_iostatus_set_err(job, error);
>          if (bs != job->bs) {
> diff --git a/include/block/blockjob.h b/include/block/blockjob.h
> index b6d4ebb..9f4b20d 100644
> --- a/include/block/blockjob.h
> +++ b/include/block/blockjob.h
> @@ -79,10 +79,14 @@ struct BlockJob {
>      bool cancelled;
>  
>      /**
> -     * Set to true if the job is either paused, or will pause itself
> -     * as soon as possible (if busy == true).
> +     * Counter for pause request. If non-zero, the block job will pause.

Why not keep the more complete comment ("If non-zero, the block job is
either paused, or if busy == true will pause itself as soon as possible")?

>       */
> -    bool paused;
> +    int pause_count;
> +
> +    /**
> +     * Set to true if the job is paused by user.

... and can be unpaused with the block-job-resume QMP command.

> +     */
> +    bool user_paused;
>  
>      /**
>       * Set to false by the job while it is in a quiescent state, where
> @@ -225,11 +229,19 @@ void block_job_pause(BlockJob *job);
>   * block_job_resume:
>   * @job: The job to be resumed.
>   *
> - * Resume the specified job.
> + * Resume the specified job.  Must be paired with a preceding block_job_pause.
>   */
>  void block_job_resume(BlockJob *job);
>  
>  /**
> + * block_job_enter:
> + * @job: The job to enter.
> + *
> + * Continue the specified job by entering the coroutine.
> + */
> +void block_job_enter(BlockJob *job);
> +
> +/**
>   * block_job_event_cancelled:
>   * @job: The job whose information is requested.
>   *
> 

Apart from this,

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>