HP-UX Reference (11i v1 05/09) - 7 Device (Special) Files, 9 General Information, Index (vol 10)

s
scsi_ctl(7) scsi_ctl(7)
NAME
scsi_ctl - SCSI pass-through driver
DESCRIPTION
SCSI devices are controlled by a device-specific driver, when one exists. Device-specific drivers, such as
those for SCSI direct access (disk) and sequential access (tape) devices, coordinate device and driver states
to accomplish correct logical device behavior. The
scsi_ctl pass-through driver enables use of SCSI dev-
ices and commands not normally supported by these device-specific drivers.
Depending on the minor number, a successful
open() call by scsi_ctl might or might not require the
device exist and respond to a
SCSI
Inquiry command. Once open, ioctl() calls can be used to change
SCSI communication parameters or attempt
SCSI commands and other SCSI operations. Since
scsi_ctl
does not attempt to logically understand the target device,
read() and write() calls are not supported.
Except where noted, the ioctls described here are available through all
SCSI device drivers (including
device-specific drivers). Super-user privileges or device write permissions are required to use these ioctls.
All
reserved fields in the data structures associated with these ioctls must be zero-filled.
Special Device File Minor Number
The scsi_ctl driver is the preferred method to perform the SIOC_IO ioctl, rather than going through a
device-specific driver (such as sdisk). To do this, you must create the device special file for
scsi_ctl.
Use mknod(1M), substituting the values in the minor number as noted:
/usr/sbin/mknod name c 203 0x
iitl0o
where component parts of the minor number are constructed as follows:
ii Two hexadecimal digits, identifying the controlling interface card by its ‘‘Instance’’ number.
The Instance value is displayed in ioscan(1M) output, under column
I for the ‘‘Interface’’
hardware type.
t One hexadecimal digit identifying the drive (target) address.
l One hexadecimal digit identifying the logical unit number (LUN) within the device.
0 Hexadecimal digit zero, for reserved portion of the minor number.
o Optional values as follows: 0 to perform Inquiry on open to ensure the device exists (recom-
mended); or 2 to inhibit Inquiry on open.
SCSI Communication Parameters
HP-UX supports the SCSI device protocol on parallel SCSI interfaces and Fibre Channel interfaces. The SCSI
communication parameters described here might only apply to certain
SCSI interfaces and are noted as
such in the descriptions.
SCSI communication parameters control features related to communication for three different scope levels:
bus (link), target, and logical unit number (LUN). Bus communication parameters apply to all targets con-
nected to a specific bus. Target communication parameters apply to all
LUNs associated with a specific tar-
get.
LUN communication parameters apply to a specific
LUN. SCSI communication parameters apply to all
device drivers (both device-specific and
scsi_ctl).
At power-up and after being reset, all parallel SCSI devices and hosts communicate using asynchronous
data transfers. Asynchronous data transfers use request (REQ) and acknowledge (ACK) signaling. The strict
ordering of REQ and ACK signaling simplifies the communication protocol but limits I/O performance. A SCSI
target and host pair may agree to use synchronous data transfers to increase I/O performance. Synchro-
nous data transfers improve I/O performance by lessening the ordering requirements on REQs and ACKs. By
allowing multiple outstanding REQs, signal propagation delays and temporary rate imbalances are better
tolerated. To make use of synchronous data transfers, a SCSI target and host must negotiate to determine
mutually acceptable maximum REQ-ACK-offset and data-transfer rate parameters. The maximum REQ-
ACK
-offset parameter indicates the maximum allowable number of outstanding REQs. The value zero is
used to indicate asynchronous data transfer. Other values indicate synchronous data transfer. The
appropriate value is generally dependent on the size of the receive data FIFO. High values tend to improve
data transfer rates. The maximum data-transfer rate parameter indicates the ‘‘burst’’ data transfer rate
(minimum allowable time between successive synchronous data transfers). A SCSI synchronous data
transfer request (SDTR) message, used to initiate the negotiation process, is associated with the processing
of a SCSI command.
At power-up and after being reset, all parallel SCSI devices and hosts communicate using eight-bit data
transfers. A SCSI target and host pair may agree to use sixteen-bit (wide) data transfers to increase I/O
Section 7−−130 Hewlett-Packard Company − 1 − HP-UX 11i Version 1: September 2005