Re: [Qemu-devel] [PATCHv7 5/6] fw_cfg: move qdev_init_nofail() from fw_cfg_init1() to callers

[Mark Cave-Ayland]

On 03/07/17 10:39, Igor Mammedov wrote:

> On Thu, 29 Jun 2017 15:07:19 +0100
> Mark Cave-Ayland <address@hidden> wrote:
> 
>> When looking to instantiate a TYPE_FW_CFG_MEM or TYPE_FW_CFG_IO device to be
>> able to wire it up differently, it is much more convenient for the caller to
>> instantiate the device and have the fw_cfg default files already preloaded
>> during realize.
>>
>> Move fw_cfg_init1() to the end of both the fw_cfg_mem_realize() and
>> fw_cfg_io_realize() functions so it no longer needs to be called manually
>> when instantiating the device, and also rename it to fw_cfg_common_realize()
>> which better describes its new purpose.
>>
>> Since it is now the responsibility of the machine to wire up the fw_cfg 
>> device
>> it is necessary to introduce a object_property_add_child() call into
>> fw_cfg_init_io() and fw_cfg_init_mem() to link the fw_cfg device to the root
>> machine object as before.
>>
>> Finally we can now convert the asserts() preventing multiple fw_cfg devices
>> and unparented fw_cfg devices being instantiated and replace them with proper
>> error reporting at realize time. This allows us to remove FW_CFG_NAME and
>> FW_CFG_PATH since they are no longer required.
>>
>> Signed-off-by: Mark Cave-Ayland <address@hidden>
>> ---
>>  hw/nvram/fw_cfg.c |   41 +++++++++++++++++++++++++++++------------
>>  1 file changed, 29 insertions(+), 12 deletions(-)
>>
>> diff --git a/hw/nvram/fw_cfg.c b/hw/nvram/fw_cfg.c
>> index 2291121..31029ac 100644
>> --- a/hw/nvram/fw_cfg.c
>> +++ b/hw/nvram/fw_cfg.c
>> @@ -37,9 +37,6 @@
>>  
>>  #define FW_CFG_FILE_SLOTS_DFLT 0x20
>>  
>> -#define FW_CFG_NAME "fw_cfg"
>> -#define FW_CFG_PATH "/machine/" FW_CFG_NAME
>> -
>>  #define TYPE_FW_CFG     "fw_cfg"
>>  #define TYPE_FW_CFG_IO  "fw_cfg_io"
>>  #define TYPE_FW_CFG_MEM "fw_cfg_mem"
>> @@ -920,19 +917,22 @@ static int fw_cfg_unattached_at_realize(void)
>>  }
>>  
>>  
>> -static void fw_cfg_init1(DeviceState *dev)
>> +static void fw_cfg_common_realize(DeviceState *dev, Error **errp)
>>  {
>>      FWCfgState *s = FW_CFG(dev);
>>      MachineState *machine = MACHINE(qdev_get_machine());
>>      uint32_t version = FW_CFG_VERSION;
>>  
>> -    assert(!object_resolve_path(FW_CFG_PATH, NULL));
>> -
>> -    object_property_add_child(OBJECT(machine), FW_CFG_NAME, OBJECT(s), 
>> NULL);
>> -
>> -    qdev_init_nofail(dev);
>> +    if (!fw_cfg_find()) {
> maybe add comment that here, that fw_cfg_find() will return NULL if more than
> 1 device is found.

This should be the same behaviour as before, i.e. a NULL means that the
fw_cfg device couldn't be found. It seems intuitive to me from the name
of the function exactly what it does, so I don't find the lack of
comment too confusing. Does anyone else have any thoughts here?

> 
>> +        error_setg(errp, "at most one %s device is permitted", TYPE_FW_CFG);
> s/TYPE_FW_CFG/object_get_typename()/
> so it would print leaf type name 

Previously the code would add the device to the machine at FW_CFG_PATH
which was fixed at /machine/fw_cfg regardless of whether it was
fw_cfg_io or fw_cfg_mem type (see the top of fw_cfg.c).

This was a deliberate attempt to preserve the existing behaviour and if
we were to give the leaf type name I think this would be misleading,
since it implies you could have one fw_cfg_io and one fw_cfg_mem which
isn't correct.

> 
>> +        return;
>> +    }
>>  
>> -    assert(!fw_cfg_unattached_at_realize());
>> +    if (fw_cfg_unattached_at_realize()) {
> as I pointed out in v6, this condition will always be false,
> I suggest to drop 4/6 patch and this hunk here so it won't to confuse
> readers with assumption that condition might succeed.

Definitely look more closely at the fw_cfg_unattached_at_realize()
implementation in patch 4. You'll see that the check to determine if the
device is attached does not check obj->parent but checks to see if the
device exists under /machine/unattached which is what the
device_set_realised() does if the device doesn't have a parent.

I can confirm that I've given this a fairly good test with parented and
non-parented objects and it seems to work well here. Does it not work
for you in testing?

> 
>> +        error_setg(errp, "%s device must be added as a child device before "
>> +                   "realize", TYPE_FW_CFG);
>> +        return;
>> +    }
>>  
>>      fw_cfg_add_bytes(s, FW_CFG_SIGNATURE, (char *)"QEMU", 4);
>>      fw_cfg_add_bytes(s, FW_CFG_UUID, &qemu_uuid, 16);
>> @@ -965,7 +965,9 @@ FWCfgState *fw_cfg_init_io_dma(uint32_t iobase, uint32_t 
>> dma_iobase,
>>          qdev_prop_set_bit(dev, "dma_enabled", false);
>>      }
>>  
>> -    fw_cfg_init1(dev);
>> +    object_property_add_child(OBJECT(qdev_get_machine()), TYPE_FW_CFG,
>> +                              OBJECT(dev), NULL);
>> +    qdev_init_nofail(dev);
>>  
>>      sbd = SYS_BUS_DEVICE(dev);
>>      ios = FW_CFG_IO(dev);
>> @@ -1003,7 +1005,9 @@ FWCfgState *fw_cfg_init_mem_wide(hwaddr ctl_addr,
>>          qdev_prop_set_bit(dev, "dma_enabled", false);
>>      }
>>  
>> -    fw_cfg_init1(dev);
>> +    object_property_add_child(OBJECT(qdev_get_machine()), TYPE_FW_CFG,
>> +                              OBJECT(dev), NULL);
>> +    qdev_init_nofail(dev);
>>  
>>      sbd = SYS_BUS_DEVICE(dev);
>>      sysbus_mmio_map(sbd, 0, ctl_addr);
>> @@ -1033,6 +1037,7 @@ FWCfgState *fw_cfg_find(void)
>>      return FW_CFG(object_resolve_path_type("", TYPE_FW_CFG, NULL));
>>  }
>>  
>> +
>>  static void fw_cfg_class_init(ObjectClass *klass, void *data)
>>  {
>>      DeviceClass *dc = DEVICE_CLASS(klass);
>> @@ -1104,6 +1109,12 @@ static void fw_cfg_io_realize(DeviceState *dev, Error 
>> **errp)
>>                                &fw_cfg_dma_mem_ops, FW_CFG(s), "fwcfg.dma",
>>                                sizeof(dma_addr_t));
>>      }
>> +
>> +    fw_cfg_common_realize(dev, &local_err);
>> +    if (local_err) {
>> +        error_propagate(errp, local_err);
>> +        return;
>> +    }
>>  }
>>  
>>  static void fw_cfg_io_class_init(ObjectClass *klass, void *data)
>> @@ -1170,6 +1181,12 @@ static void fw_cfg_mem_realize(DeviceState *dev, 
>> Error **errp)
>>                                sizeof(dma_addr_t));
>>          sysbus_init_mmio(sbd, &FW_CFG(s)->dma_iomem);
>>      }
>> +
>> +    fw_cfg_common_realize(dev, &local_err);
>> +    if (local_err) {
>> +        error_propagate(errp, local_err);
>> +        return;
>> +    }
>>  }
>>  
>>  static void fw_cfg_mem_class_init(ObjectClass *klass, void *data)
> patch looks good, with above comments fixed:

Great, thanks! I think there is some misunderstanding about the points
above so I'd be interested to hear your further comments.

> Reviewed-by: Igor Mammedov <address@hidden>


ATB,

Mark.