cam probe sequence

[Jack]

Hello all,

I'm trying to understand the probe sequence of a scsi device, say
a scsi hard drive( with SPI/SAS/FC interface).

I'm particularly interested in probe sequence of a device which is
attached to the system _after_ FreeBSD has booted completely.
(ie post-boot probing.)

While going through the source of cam subsystem,  a few
questions arose in my understanding.

( The relevant files I found are cam/cam_xpt.c, cam/cam_periph.c
  and cam/scsi/scsi_xpt.c or cam/ata/ata_xpt.c in case of (S)ATA
 drives. )

As far as I could got till now, it seems that struct cam_et and
struct cam_ed are _always_ created even _before_ the probing of
device commences.

But how does cam sub-system get to know that a device got
attached to the system, so that it creates struct cam_et and
struct cam_ed in advance, and _then_ probes the device.

Is it something like a event notfication at hardware level that
the HBA driver passes to cam sub-system which notifies cam
sub-system that a device has recently been attached.

If it is true, then does all SPI/SAS/FC/(S)ATA  HBAs support
such event notification -- something like a standard thing
in SPI/SAS/FC/(S)ATA world.

If it is not so, then does userland have to intiate a scan after
device is attached, so that during scanning the cam-subsystem
 get to know that Oh! there is a device we are meeting first time.
In other words, _until_ userland instructs cam subsystem to scan
all the buses by XPT_SCAN_BUS ccb through CAMIOCOMMAND
ioctl of /dev/xpt0, the struct cam_et and struct cam_ed will not
get created. Is it so?
But in this case also,  does cam-subsystem creates
struct cam_et and struct cam_ed before probing the device?.

In case of SPI/SAS/FC hard drives the probe code is in
cam/scsi/scsi_xpt.c  While reading this source file it
also seems to me that a struct cam_periph is also created
as soon as struct cam_et and struct cam_ed are created.
This also happens before probing of device commences.
Is it the pass device that is created even before probing begins.
Then after probing and determining the type of device - e.g. disk,
cd-rom, etc, then the appropriate peripheral device(da, cd, etc. ) is
 created for the probed device. Is it so?


It would be really helpful if someone could clear these things,
specially from the instant the device -say a hard disk; is attached,
to the instant the pass device and da device are created and
probing of this hard disk commences or finishes.



Regards
-- 
Jack