— CAM application passthrough
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.
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
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
- 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
- Character device nodes for the pass
driver. There should be one of these for each device accessed through the
The CAM passthrough driver first appeared in FreeBSD
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.