Re: [linux-iscsi-devel] Re: [PATCH RFC] replace ioctl for sysfs take 2

[James Bottomley <James.Bottomley@SteelEye.com>]

On Mon, 2004-09-06 at 18:48, Mike Christie wrote:
> For bus usage and virtual drivers like this and scsi_debug, would it be 
> better to just have a single virtual bus for all virtual drivers to 
> share, or should we instead modify the scsi_bus so that it can handle 
> ULD and virtual LLD struct device_driver attachments. Today, the 
> scsi_bus seems to be used for upper layer drivers becuase they are the 
> only ones needing to attach UL struct device_drivers to scsi devices, 
> but instead of scsi_debug or iscsi-sfnet implementing its own virtual 
> bus the scsi_bus could manage a low level virtual driver's scsi_host 
> parent's devices.
> 
> Also, with James's patch we have scsi_devices and scsi_targets off the 
> scsi_bus, does scsi_host's shost_gendev belong there too? What is the 
> purpose of the scsi_bus?> 

Using a virtual bus only makes sense when you actually have multiple
virtual drivers that need to attach.  Thus, we only have one virtual
scsi bus (scsi_bus_type) and it's only used for the generic device
embedded in struct scsi_device.  We use it only to attach the various
ULDs.  The host and target devices just have a null bus.

I'm not quite sure what you want to use another bus type for?  It sounds
like you really want to be using a device class instead.  The difference
is

- classes provide (potentially multiple) interfaces to existing devices;
- busses are used for keeping track of attached devices and matching
them to their drivers.

Unless you really have a use for device matching and driver attachment,
you probably just want to stick with classes.

James