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PASS(4) Device Drivers Manual PASS(4)

pass — CAM application passthrough driver

device pass
device pass2 at scbus0 target 3 unit 0

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 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.

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

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.
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're issuing this ioctl. It is probably more useful to issue this ioctl through the xpt(4) device.

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

None.

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

The CAM passthrough driver first appeared in FreeBSD 3.0.

Kenneth Merry <ken@FreeBSD.org>

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 DragonFly-5.6.1