Re: [PATCH v2 2/2] spapr: use DEVICE_UNPLUG_ERROR to report unplug errors

[Markus Armbruster <armbru@redhat.com>]

Daniel Henrique Barboza <danielhb413@gmail.com> writes:

> Linux Kernel 5.12 is now unisolating CPU DRCs in the device_removal
> error path, signalling that the hotunplug process wasn't successful.
> This allow us to send a DEVICE_UNPLUG_ERROR in drc_unisolate_logical()
> to signal this error to the management layer.
>
> We also have another error path in spapr_memory_unplug_rollback() for
> configured LMB DRCs. Kernels older than 5.13 will not unisolate the LMBs
> in the hotunplug error path, but it will reconfigure them.  Let's send
> the DEVICE_UNPLUG_ERROR event in that code path as well to cover the
> case of older kernels.
>
> Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
> ---
>  hw/ppc/spapr.c     |  2 +-
>  hw/ppc/spapr_drc.c | 15 +++++++++------
>  2 files changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> index c23bcc4490..29aa2f467d 100644
> --- a/hw/ppc/spapr.c
> +++ b/hw/ppc/spapr.c
> @@ -3639,7 +3639,7 @@ void spapr_memory_unplug_rollback(SpaprMachineState *spapr, DeviceState *dev)
>       */
>      qapi_error = g_strdup_printf("Memory hotunplug rejected by the guest "
>                                   "for device %s", dev->id);
> -    qapi_event_send_mem_unplug_error(dev->id, qapi_error);
> +    qapi_event_send_device_unplug_error(dev->id, qapi_error);

Incompatible change: we now emit DEVICE_UNPLUG_ERROR instead of
MEM_UNPLUG_ERROR.  Intentional?

If yes, we need a release note.

To avoid the incompatible, we can emit both, and deprecate
MEM_UNPLUG_ERROR.

What about the MEM_UNPLUG_ERROR in acpi_memory_hotplug_write()?

>  }
>  
>  /* Callback to be called during DRC release. */
> diff --git a/hw/ppc/spapr_drc.c b/hw/ppc/spapr_drc.c
> index a2f2634601..0e1a8733bc 100644
> --- a/hw/ppc/spapr_drc.c
> +++ b/hw/ppc/spapr_drc.c
> @@ -17,6 +17,8 @@
>  #include "hw/ppc/spapr_drc.h"
>  #include "qom/object.h"
>  #include "migration/vmstate.h"
> +#include "qapi/error.h"
> +#include "qapi/qapi-events-machine.h"
>  #include "qapi/visitor.h"
>  #include "qemu/error-report.h"
>  #include "hw/ppc/spapr.h" /* for RTAS return codes */
> @@ -160,6 +162,10 @@ static uint32_t drc_unisolate_logical(SpaprDrc *drc)
>           * means that the kernel is refusing the removal.
>           */
>          if (drc->unplug_requested && drc->dev) {
> +            const char qapi_error_fmt[] = "Device hotunplug rejected by the "
> +                                          "guest for device %s";
> +            g_autofree char *qapi_error = NULL;
> +
>              if (spapr_drc_type(drc) == SPAPR_DR_CONNECTOR_TYPE_LMB) {
>                  spapr = SPAPR_MACHINE(qdev_get_machine());
>  
> @@ -167,13 +173,10 @@ static uint32_t drc_unisolate_logical(SpaprDrc *drc)
>              }
>  
>              drc->unplug_requested = false;
> -            error_report("Device hotunplug rejected by the guest "
> -                         "for device %s", drc->dev->id);
> +            error_report(qapi_error_fmt, drc->dev->id);
>  
> -            /*
> -             * TODO: send a QAPI DEVICE_UNPLUG_ERROR event when
> -             * it is implemented.
> -             */
> +            qapi_error = g_strdup_printf(qapi_error_fmt, drc->dev->id);
> +            qapi_event_send_device_unplug_error(drc->dev->id, qapi_error);
>          }
>  
>          return RTAS_OUT_SUCCESS; /* Nothing to do */

Reporting both to stderr and QMP is odd.  Can you describe a use case
where the report to stderr is useful?