Re: [PATCH 08/12] hw/xen: do not repeatedly try to create a failing backend device

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On 16/10/2023 16:19, David Woodhouse wrote:
From: David Woodhouse <dwmw@xxxxxxxxxxxx>

If xen_backend_device_create() fails to instantiate a device, the XenBus
code will just keep trying over and over again each time the bus is
re-enumerated, as long as the backend appears online and in
XenbusStateInitialising.

The only thing which prevents the XenBus code from recreating duplicates
of devices which already exist, is the fact that xen_device_realize()
sets the backend state to XenbusStateInitWait. If the attempt to create
the device doesn't get *that* far, that's when it will keep getting
retried.

My first thought was to handle errors by setting the backend state to
XenbusStateClosed, but that doesn't work for XenConsole which wants to
*ignore* any device of type != "ioemu" completely.

So, make xen_backend_device_create() *keep* the XenBackendInstance for a
failed device, and provide a new xen_backend_exists() function to allow
xen_bus_type_enumerate() to check whether one already exists before
creating a new one.

Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
---
  hw/xen/xen-backend.c         | 27 +++++++++++++++++++++------
  hw/xen/xen-bus.c             |  3 ++-
  include/hw/xen/xen-backend.h |  1 +
  3 files changed, 24 insertions(+), 7 deletions(-)


Reviewed-by: Paul Durrant <paul@xxxxxxx>




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