[dm-devel] Re: [PATCH 4/9] scsi_dh: add skeleton for SCSI Device Handlers

[Mike Anderson <andmike linux vnet ibm com>]

Mike Christie <michaelc cs wisc edu> wrote:
> Chandra Seetharaman wrote:
>>  	 * mainly associated with tapes and returned SUCCESS.
>> Index: linux-2.6.24-rc8/drivers/scsi/scsi_sysfs.c
>> ===================================================================
>> --- linux-2.6.24-rc8.orig/drivers/scsi/scsi_sysfs.c
>> +++ linux-2.6.24-rc8/drivers/scsi/scsi_sysfs.c
>> @@ -951,6 +951,49 @@ int scsi_register_interface(struct class
>>  }
>>  EXPORT_SYMBOL(scsi_register_interface);
>>  +static int scsi_dh_notifier_add(struct device *dev, void *data)
>> +{
>> +	struct scsi_device_handler *sdev_dh = data;
>> +
>> +	sdev_dh->nb.notifier_call(&sdev_dh->nb, BUS_NOTIFY_ADD_DEVICE, dev);
>> +
>> +	return 0;
>> +}
>> +
>> +int scsi_register_device_handler(struct scsi_device_handler *sdev_dh)
>> +{
>> +	int ret;
>> +
>> +	ret = bus_register_notifier(&scsi_bus_type, &sdev_dh->nb);
>> +
>> +	bus_for_each_dev(&scsi_bus_type, NULL, sdev_dh, scsi_dh_notifier_add);
>> +
>> +	return ret;
>> +}
>> +EXPORT_SYMBOL(scsi_register_device_handler);
>> +
>> +static int scsi_dh_notifier_remove(struct device *dev, void *data)
>> +{
>> +	struct scsi_device_handler *sdev_dh = data;
>> +
>> +	sdev_dh->nb.notifier_call(&sdev_dh->nb, BUS_NOTIFY_DEL_DEVICE, dev);
>> +
>> +	return 0;
>> +}
>> +
>> +int scsi_unregister_device_handler(struct scsi_device_handler *sdev_dh)
>> +{
>> +	int ret;
>> +
>> +	ret = bus_unregister_notifier(&scsi_bus_type, &sdev_dh->nb);
>> +
>> +	bus_for_each_dev(&scsi_bus_type, NULL, sdev_dh,
>> +					scsi_dh_notifier_remove);
>> +
>> +	return ret;
>> +}
>> +EXPORT_SYMBOL(scsi_unregister_device_handler);
>> +
>
> Did this end up solving the problem I was hitting where when using the 
> other driver model stuff like is used with the SCSI upper layer drivers. 
> The problem where the hw handler module had to be loaded before finding 
> devices and had to be loaded before sd.c?

Yes this update was to have the handler add routine called prior to the
upper level drivers probe routine. In device_add
blocking_notifier_call_chain is called prior to bus_attach_device which
leads to the upper level drivers probe routine being called.

The bus_register_notifier will handle new devices showing up and the
bus_for_each_dev is used to sync up with already probed devices. Obviously
loading late will not be able to handle issues during the device probe
if a device needs that type of handling.

-andmike
--
Michael Anderson
andmike linux vnet ibm com