pass (4)

Leading comments

Copyright (c) 1998, 1999 Kenneth D. Merry.
All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
   notice, this list of conditions and the following disclaimer in the
   documentation a...

(The comments found at the beginning of the groff file "man4/pass.4freebsd".)

NAME

pass - CAM application passthrough driver

SYNOPSIS

device pass

DESCRIPTION

The driver provides a way for userland applications to issue CAM CCBs to the kernel.

Since the driver allows direct access to the CAM subsystem, system administrators should exercise caution when granting access to this driver. If used improperly, this driver can allow userland applications to crash a machine or cause data loss.

The driver attaches to every SCSI device found in the system. Since it attaches to every device, it provides a generic means of accessing SCSI devices, and allows the user to access devices which have no "standard" peripheral driver associated with them.

KERNEL CONFIGURATION

It is only necessary to configure one device in the kernel; devices are automatically allocated as SCSI devices are found.

IOCTLS

CAMIOCOMMAND

This ioctl takes most kinds of CAM CCBs and passes them through to the CAM transport layer for action. Note that some CCB types are not allowed through the passthrough device, and must be sent through the xpt(4) device instead. Some examples of xpt-only CCBs are XPT_SCAN_BUS, XPT_DEV_MATCH, XPT_RESET_BUS, XPT_SCAN_LUN, XPT_ENG_INQ, and XPT_ENG_EXEC. These CCB types have various attributes that make it illogical or impossible to service them through the passthrough interface.

CAMGETPASSTHRU

This ioctl takes an XPT_GDEVLIST CCB, and returns the passthrough device corresponding to the device in question. Although this ioctl is available through the driver, it is of limited use, since the caller must already know that the device in question is a passthrough device if they are issuing this ioctl. It is probably more useful to issue this ioctl through the xpt(4) device.

FILES

/dev/pass n

Character device nodes for the driver. There should be one of these for each device accessed through the CAM subsystem.

DIAGNOSTICS

None.

SEE ALSO

cam(3), cam(4), cam_cdbparse3, xpt(4), camcontrol(8)

HISTORY

The CAM passthrough driver first appeared in Fx 3.0 .

AUTHORS

An Kenneth Merry Aq ken@FreeBSD.org

BUGS

It might be nice to have a way to asynchronously send CCBs through the passthrough driver. This would probably require some sort of read/write interface or an asynchronous ioctl interface.