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

[Stefan Hajnoczi]

On Fri, Apr 03, 2015 at 04:13:55PM +0200, Paolo Bonzini wrote:
> 
> 
> 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 <address@hidden>
> > ---
> >  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.

I squashed in your suggestions.

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