Re: Attachment order of scsibus*

[Valery Ushakov <uwe%stderr.spb.ru@localhost>]

On Fri, Apr 11, 2025 at 11:05:19 +0200, Edgar Fuß wrote:

> > You can create a custom kernel with a fixed set of attachments
> But how in this case?
> There’s some magic
>         scsibus* at scsi*
> but no scsi at anything.

scsi is not device, it's an attribute.  In Java terms, thinks classes
vs. interfaces.  config(5) is a bit dense, but it documents all this.

conf/files has:

  define scsi ...
  device mpt: scsi

which is kinda "class mpt extends device implements scsi".  As
config(5) says:

  There is a special class of attribute, named interface attribute, which
  represents a hook that allows a device to attach to (i.e., be a child of)
  another device.

and here "scsi" is such an "interface attribute".


sys/dev/scsipi/files.scsipi has:

    device scsibus ...
    attach scsibus at scsi

that tries to attach scsibus to any device that "implements scsi"
interface attribute.

This is may be a bit unfortunate from the readability point of view,
as the name "scsi" just seemingly appears out of nowhere in the kernel
config file, b/c its definition is somwhere in sys/**/files* that you
don't see when you read/edit a kernel config.  Think of this as a name
that comes from the "standard library", like printf, of FILE :) (sorry
for mixing Java and C metaphors).

-uwe