pass(4)

NAME

pass - CAM application passthrough driver

SYNOPSIS

device pass

DESCRIPTION

The pass driver provides a way for userland applications to

issue CAM
CCBs to the kernel.

Since the pass driver allows direct access to the CAM sub

system, 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 pass 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 pass device in the

kernel; pass
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 ac

tion. 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_EX

EC. 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 de

vice in question. Although this ioctl is available

through the pass
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/passn Character device nodes for the pass driver.

There should be

one of these for each device accessed through

the CAM subsystem.

DIAGNOSTICS

None.

SEE ALSO

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

HISTORY

The CAM passthrough driver first appeared in FreeBSD 3.0.

AUTHORS

Kenneth Merry <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.

BSD October 10, 1998

BSD