Re: [Qemu-devel] [PATCH v2 2/2] ipmi: Add a UUID device property

[Corey Minyard]

On Wed, Jul 03, 2019 at 03:26:25PM +0100, Daniel P. Berrangé wrote:
> On Mon, Jul 01, 2019 at 01:31:00PM -0500, address@hidden wrote:
> > From: Corey Minyard <address@hidden>
> > 
> > Using the UUID that qemu generates probably isn't the best thing
> > to do, allow it to be passed in via properties, and use QemuUUID
> > for the type.
> 
> AFAICT, QEMU isn't generating a UUID in the current code.

Yeah, it doesn't appear to.

> 
> The device is taking the UUID that the user has set
> explicitly via the --uuid argument to QEMU. If --uuid
> is not set, then it is leaving it all zeros.
> 
> Defaulting to the UUID from --uuid looks quite reasonable
> to me & I don't think we should break that current usage.

I originally thought that, but thinking it through some more,
that's not the way real systems work.  The system UUID and the
BMC UUID are generally (probably always) different.

Plus, defaulting it to the system UUID might result in a
surprise for the user.  In retrospect, I think it's better
to leave the UUID unset unless explicitly set by the user.

> 
> I can see justification for being able to further override
> that default with a device level property though.
> 
> 
> > If the UUID is not set, return an unsupported command error.  This
> > way we are not providing an all-zero (or randomly generated) GUID
> > to the IPMI user.  This lets the host fall back to the other
> > method of using the get device id command to determind the BMC
> > being accessed.
> 
> Reporting an error would be a guest ABI regression from current QEMU
> behaviour for anyone who is using the IPMI device right now, without
> --uuid.

Actually, it would only be a regression for anyone using --uuid.  If
the system UUID is all zero, then it will return an error currently.

> 
> I'm not sure how much we care about guest ABI preservation for
> the IPIMI device right now though ? Does it support migration
> at all ?

It does support migration, but the UUID is not migrated, since it
is a property set on the command line.  That means if you
migrated with --uuid and didn't set the IPMI UUID on the command
line for the migration target, it would change behavior.

ABI preservation is probably not important for this particular
feature, but there is a workaround.

-corey

> 
> > 
> > Signed-off-by: Corey Minyard <address@hidden>
> > Cc: Cédric Le Goater <address@hidden>
> > Cc: David Gibson <address@hidden>
> > Cc: Michael S. Tsirkin <address@hidden>
> > Cc: Paolo Bonzini <address@hidden>
> > ---
> >  hw/ipmi/ipmi_bmc_sim.c | 22 ++++++++++++++--------
> >  qemu-options.hx        | 10 +++++++---
> >  2 files changed, 21 insertions(+), 11 deletions(-)
> > 
> > diff --git a/hw/ipmi/ipmi_bmc_sim.c b/hw/ipmi/ipmi_bmc_sim.c
> > index 1980536517..007e2c6588 100644
> > --- a/hw/ipmi/ipmi_bmc_sim.c
> > +++ b/hw/ipmi/ipmi_bmc_sim.c
> > @@ -221,7 +221,7 @@ struct IPMIBmcSim {
> >      uint8_t restart_cause;
> >  
> >      uint8_t acpi_power_state[2];
> > -    uint8_t uuid[16];
> > +    QemuUUID uuid;
> >  
> >      IPMISel sel;
> >      IPMISdr sdr;
> > @@ -937,8 +937,19 @@ static void get_device_guid(IPMIBmcSim *ibs,
> >  {
> >      unsigned int i;
> >  
> > +    /* An uninitialized uuid is all zeros, use that to know if it is set. 
> > */
> >      for (i = 0; i < 16; i++) {
> > -        rsp_buffer_push(rsp, ibs->uuid[i]);
> > +        if (ibs->uuid.data[i]) {
> > +            goto uuid_set;
> > +        }
> > +    }
> > +    /* No uuid is set, return an error. */
> > +    rsp_buffer_set_error(rsp, IPMI_CC_INVALID_CMD);
> > +    return;
> > +
> > + uuid_set:
> > +    for (i = 0; i < 16; i++) {
> > +        rsp_buffer_push(rsp, ibs->uuid.data[i]);
> >      }
> >  }
> >  
> > @@ -1980,12 +1991,6 @@ static void ipmi_sim_realize(DeviceState *dev, Error 
> > **errp)
> >      ibs->acpi_power_state[0] = 0;
> >      ibs->acpi_power_state[1] = 0;
> >  
> > -    if (qemu_uuid_set) {
> > -        memcpy(&ibs->uuid, &qemu_uuid, 16);
> > -    } else {
> > -        memset(&ibs->uuid, 0, 16);
> > -    }
> > -
> >      ipmi_init_sensors_from_sdrs(ibs);
> >      register_cmds(ibs);
> >  
> > @@ -2005,6 +2010,7 @@ static Property ipmi_sim_properties[] = {
> >      DEFINE_PROP_UINT8("fwrev2", IPMIBmcSim, fwrev2, 0),
> >      DEFINE_PROP_UINT32("mfg_id", IPMIBmcSim, mfg_id, 0),
> >      DEFINE_PROP_UINT16("product_id", IPMIBmcSim, product_id, 0),
> > +    DEFINE_PROP_UUID_NODEFAULT("guid", IPMIBmcSim, uuid),
> >      DEFINE_PROP_END_OF_LIST(),
> >  };
> >  
> > diff --git a/qemu-options.hx b/qemu-options.hx
> > index 0d8beb4afd..ec56ab8f6f 100644
> > --- a/qemu-options.hx
> > +++ b/qemu-options.hx
> > @@ -700,7 +700,7 @@ possible drivers and properties, use @code{-device 
> > help} and
> >  @code{-device @var{driver},help}.
> >  
> >  Some drivers are:
> > -@item -device 
> > ipmi-bmc-sim,id=@var{id}[,slave_addr=@var{val}][,sdrfile=@var{file}][,furareasize=@var{val}][,furdatafile=@var{file}]
> > +@item -device 
> > ipmi-bmc-sim,id=@var{id}[,slave_addr=@var{val}][,sdrfile=@var{file}][,furareasize=@var{val}][,furdatafile=@var{file}][,guid=@var{uuid}]
> >  
> >  Add an IPMI BMC.  This is a simulation of a hardware management
> >  interface processor that normally sits on a system.  It provides
> > @@ -713,8 +713,8 @@ controllers.  If you don't know what this means, it is 
> > safe to ignore
> >  it.
> >  
> >  @table @option
> > -@item bmc=@var{id}
> > -The BMC to connect to, one of ipmi-bmc-sim or ipmi-bmc-extern above.
> > +@item id=@var{id}
> > +The BMC id for interfaces to use this device.
> >  @item slave_addr=@var{val}
> >  Define slave address to use for the BMC.  The default is 0x20.
> >  @item sdrfile=@var{file}
> > @@ -723,6 +723,10 @@ file containing raw Sensor Data Records (SDR) data. 
> > The default is none.
> >  size of a Field Replaceable Unit (FRU) area.  The default is 1024.
> >  @item frudatafile=@var{file}
> >  file containing raw Field Replaceable Unit (FRU) inventory data. The 
> > default is none.
> > +@item guid=@var{uuid}
> > +value for the GUID for the BMC, in standard UUID format.  If this is set,
> > +get "Get GUID" command to the BMC will return it.  Otherwise "Get GUID"
> > +will return an error.
> >  @end table
> >  
> >  @item -device 
> > ipmi-bmc-extern,id=@var{id},chardev=@var{id}[,slave_addr=@var{val}]
> > -- 
> > 2.17.1
> > 
> > 
> 
> Regards,
> Daniel
> -- 
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