table of contents
other sections
PASS(4) | Device Drivers Manual | PASS(4) |
NAME¶
pass
—
CAM application passthrough driver
SYNOPSIS¶
device pass
DESCRIPTION¶
Thepass
driver provides a way for userland
applications to issue CAM CCBs to the kernel.
Since the pass
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 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 onepass
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 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
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(4), 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.October 10, 1998 | Debian |