Re: [Qemu-devel] [RFC v4 05/21] blockjobs: add state transition table

[Kevin Wolf <kwolf@redhat.com>]

Am 24.02.2018 um 00:51 hat John Snow geschrieben:
> The state transition table has mostly been implied. We're about to make
> it a bit more complex, so let's make the STM explicit instead.
> 
> Perform state transitions with a function that for now just asserts the
> transition is appropriate.
> 
> Transitions:
> Undefined -> Created: During job initialization.
> Created   -> Running: Once the job is started.
>                       Jobs cannot transition from "Created" to "Paused"
>                       directly, but will instead synchronously transition
>                       to running to paused immediately.
> Running   -> Paused:  Normal workflow for pauses.
> Running   -> Ready:   Normal workflow for jobs reaching their sync point.
>                       (e.g. mirror)
> Ready     -> Standby: Normal workflow for pausing ready jobs.
> Paused    -> Running: Normal resume.
> Standby   -> Ready:   Resume of a Standby job.
> 
> 
> +---------+
> |UNDEFINED|
> +--+------+
>    |
> +--v----+
> |CREATED|
> +--+----+
>    |
> +--v----+     +------+
> |RUNNING<----->PAUSED|
> +--+----+     +------+
>    |
> +--v--+       +-------+
> |READY<------->STANDBY|
> +-----+       +-------+
> 
> 
> Notably, there is no state presently defined as of this commit that
> deals with a job after the "running" or "ready" states, so this table
> will be adjusted alongside the commits that introduce those states.
> 
> Signed-off-by: John Snow <jsnow@redhat.com>
> ---
>  block/trace-events |  3 +++
>  blockjob.c         | 42 ++++++++++++++++++++++++++++++++++++------
>  2 files changed, 39 insertions(+), 6 deletions(-)
> 
> diff --git a/block/trace-events b/block/trace-events
> index 02dd80ff0c..b75a0c8409 100644
> --- a/block/trace-events
> +++ b/block/trace-events
> @@ -4,6 +4,9 @@
>  bdrv_open_common(void *bs, const char *filename, int flags, const char *format_name) "bs %p filename \"%s\" flags 0x%x format_name \"%s\""
>  bdrv_lock_medium(void *bs, bool locked) "bs %p locked %d"
>  
> +# blockjob.c
> +block_job_state_transition(void *job,  int ret, const char *legal, const char *s0, const char *s1) "job %p (ret: %d) attempting %s transition (%s-->%s)"
> +
>  # block/block-backend.c
>  blk_co_preadv(void *blk, void *bs, int64_t offset, unsigned int bytes, int flags) "blk %p bs %p offset %"PRId64" bytes %u flags 0x%x"
>  blk_co_pwritev(void *blk, void *bs, int64_t offset, unsigned int bytes, int flags) "blk %p bs %p offset %"PRId64" bytes %u flags 0x%x"
> diff --git a/blockjob.c b/blockjob.c
> index 1be9c20cff..d745b3bb69 100644
> --- a/blockjob.c
> +++ b/blockjob.c
> @@ -28,6 +28,7 @@
>  #include "block/block.h"
>  #include "block/blockjob_int.h"
>  #include "block/block_int.h"
> +#include "block/trace.h"
>  #include "sysemu/block-backend.h"
>  #include "qapi/error.h"
>  #include "qapi/qmp/qerror.h"
> @@ -41,6 +42,34 @@
>   * block_job_enter. */
>  static QemuMutex block_job_mutex;
>  
> +/* BlockJob State Transition Table */
> +bool BlockJobSTT[BLOCK_JOB_STATUS__MAX][BLOCK_JOB_STATUS__MAX] = {
> +                                          /* U, C, R, P, Y, S */
> +    /* U: */ [BLOCK_JOB_STATUS_UNDEFINED] = {0, 1, 0, 0, 0, 0},

Even at the end of the series, this is the only use of
BLOCK_JOB_STATUS_UNDEFINED.

> +    /* C: */ [BLOCK_JOB_STATUS_CREATED]   = {0, 0, 1, 0, 0, 0},
> +    /* R: */ [BLOCK_JOB_STATUS_RUNNING]   = {0, 0, 0, 1, 1, 0},
> +    /* P: */ [BLOCK_JOB_STATUS_PAUSED]    = {0, 0, 1, 0, 0, 0},
> +    /* Y: */ [BLOCK_JOB_STATUS_READY]     = {0, 0, 0, 0, 0, 1},
> +    /* S: */ [BLOCK_JOB_STATUS_STANDBY]   = {0, 0, 0, 0, 1, 0},
> +};
> +
> +static void block_job_state_transition(BlockJob *job, BlockJobStatus s1)
> +{
> +    BlockJobStatus s0 = job->status;
> +    if (s0 == s1) {
> +        return;
> +    }
> +    assert(s1 >= 0 && s1 <= BLOCK_JOB_STATUS__MAX);
> +    trace_block_job_state_transition(job, job->ret, BlockJobSTT[s0][s1] ?
> +                                     "allowed" : "disallowed",
> +                                     qapi_enum_lookup(&BlockJobStatus_lookup,
> +                                                      s0),
> +                                     qapi_enum_lookup(&BlockJobStatus_lookup,
> +                                                      s1));
> +    assert(BlockJobSTT[s0][s1]);
> +    job->status = s1;
> +}
> +
>  static void block_job_lock(void)
>  {
>      qemu_mutex_lock(&block_job_mutex);
> @@ -320,7 +349,7 @@ void block_job_start(BlockJob *job)
>      job->pause_count--;
>      job->busy = true;
>      job->paused = false;
> -    job->status = BLOCK_JOB_STATUS_RUNNING;
> +    block_job_state_transition(job, BLOCK_JOB_STATUS_RUNNING);
>      bdrv_coroutine_enter(blk_bs(job->blk), job->co);
>  }
>  
> @@ -704,6 +733,7 @@ void *block_job_create(const char *job_id, const BlockJobDriver *driver,
>      job->refcnt        = 1;
>      job->manual        = (flags & BLOCK_JOB_MANUAL);
>      job->status        = BLOCK_JOB_STATUS_CREATED;
> +    block_job_state_transition(job, BLOCK_JOB_STATUS_CREATED);

So did you intend to start with BLOCK_JOB_STATUS_UNDEFINED and then
transition to BLOCK_JOB_STATUS_CREATED?

Or should we completely remove BLOCK_JOB_STATUS_UNDEFINED, keep the
initialisation and not call block_job_state_transition() here?

Kevin