scsi_ctl(7) scsi_ctl(7)
NAME [Toc] [Back]
scsi_ctl - SCSI pass-through driver
DESCRIPTION [Toc] [Back]
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 devices 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). Superuser
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 [Toc] [Back]
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 0xiitl0o
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 (recommended); or 2 to
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inhibit Inquiry on open.
SCSI Communication Parameters [Toc] [Back]
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 connected to a specific bus. Target communication
parameters apply to all LUNs associated with a specific target. 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.
Synchronous 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 performance. To make use of wide data transfers, a SCSI target
and host must negotiate to determine a mutually acceptable data
transfer width parameter. A SCSI wide data transfer request (WDTR)
message, used to initiate the negotiation process, is associated with
the processing of a SCSI command.
Some SCSI devices are able to simultaneously manage multiple active
commands. Such a device has a command queue that holds commands for
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processing. Command queuing can improve I/O performance by reducing
the time spent by the device waiting for new commands from the host.
Note that command queuing might not improve I/O performance
substantially for devices that support ``read-ahead'' and
``immediate-reporting'' (see scsi_disk(7) and scsi_tape(7)). The SCSI
device and host use command tags to correctly manage these multiple
simultaneously active commands. At all times when command queuing is
in effect, each active command being handled by a specific LUN has a
unique command tag.
SCSI devices indicate their ability to support the special
communication features described above in their SCSI INQUIRY command
data. Normally the SCSI INQUIRY command data and negotiation
protocols allow hosts and devices to determine the optimal
communication parameters so that I/O performance is maximized. The
current operating communication parameters may be determined by use of
the: SIOC_GET_LUN_PARMS, SIOC_GET_TGT_PARMS, and SIOC_GET_BUS_PARMS
ioctls.
Occasionally, it is desirable to limit SCSI communication parameters
to work around a communication problem or to provide external insight
in determining optimal parameters. SCSI communication parameter limit
suggestions can be specified by use of the: SIOC_SET_LUN_LIMITS,
SIOC_SET_TGT_LIMITS, and SIOC_SET_BUS_LIMITS ioctls. Note that there
might be substantial differences between specified communication
parameter limit suggestions and the corresponding actual current
communication parameters being used for communication. These
differences are a result of device-specific driver capabilities,
interface driver capabilities, interface hardware capabilities, device
capabilities, delays due to the negotiation process, delays due to
currently active commands, and delays due to commands waiting to be
sent to devices. Note that communication parameter limit suggestions
might not survive between close() and open() calls, when no SCSI
device drivers (device-specific or scsi_ctl) have associated LUN(s)
open.
The current SCSI communication parameter limit suggestions may be
determined by use of the SIOC_GET_LUN_LIMITS, SIOC_GET_TGT_LIMITS, and
SIOC_GET_BUS_LIMITS ioctls.
Logical unit communication parameters may be managed by use of the
SIOC_GET_LUN_PARMS, SIOC_SET_LUN_LIMITS, and SIOC_GET_LUN_LIMITS
ioctls.
The SIOC_GET_LUN_PARMS ioctl indicates the current LUN communication
parameter values. The max_q_depth field indicates whether or not
tagged queuing is enabled, and if enabled, the maximum number of
simultaneously active commands allowed. When max_q_depth is zero,
tagged queuing is disabled. When it is one, tags are being used but
commands are still being serially processed. When it is greater than
one, tags are being used and max_q_depth specifies the maximum number
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of simultaneously active commands allowed.
The SIOC_SET_LUN_LIMITS ioctl may be used to provide LUN communication
parameter limit suggestions. The max_q_depth field indicates whether
or not tagged queuing should be enabled, and if enabled, the maximum
number of simultaneously active commands that should be allowed. The
SIOC_GET_LUN_LIMITS ioctl indicates the current LUN communication
parameter limit suggestions.
Target communication parameters may be managed by use of the
SIOC_GET_TGT_PARMS, SIOC_SET_TGT_LIMITS, and SIOC_GET_TGT_LIMITS
ioctls to any associated LUN.
The SIOC_GET_TGT_PARMS ioctl indicates the current target
communication parameter values. The width, reqack_offset, and
xfer_rate fields indicate the currently negotiated data transfer
parameters. When width is eight, narrow transfers are in effect.
When it is sixteen, wide transfers are in effect. When reqack_offset
is zero, asynchronous transfers are in effect and xfer_rate is
meaningless. When reqack_offset is non-zero, synchronous transfers
are in effect and the maximum ``burst'' data transfer rate is
xfer_rate words per second, where the size of a word is as indicated
in width.
The SIOC_SET_TGT_LIMITS ioctl specifies the target communication
parameter limit suggestions. The max_width field specifies maximum
bus width that should be used for data transfers. The
max_reqack_offset field specifies the maximum number of outstanding
REQs that should be attempted during data transfers. The
max_xfer_rate field specifies the maximum ``burst'' data rate that
should be allowed during synchronous data transfers. The
SIOC_GET_TGT_LIMITS ioctl indicates the current target communication
parameter limit suggestions. The width, reqack_offset, xfer_rate,
max_width, max_reqack_offset, max_xfer_rate fields only apply to
parallel SCSI.
Bus communication parameters may be managed by use of the
SIOC_GET_BUS_PARMS, SIOC_SET_BUS_LIMITS, and SIOC_GET_BUS_LIMITS
ioctls to any associated LUN.
The SIOC_GET_BUS_PARMS ioctl indicates the current bus communication
parameter values. The max_width field indicates the maximum data
transfer width that will be attempted for data transfers to any target
device connected to the associated bus. The max_reqack_offset field
indicates the maximum number of outstanding REQs that will be
attempted during data transfers to any target device connected to the
associated bus. The max_xfer_rate field indicates the maximum
``burst'' data transfer rate that will be attempted for data transfers
to any target device connected to the associated bus.
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The SIOC_SET_BUS_LIMITS ioctl specifies the bus communication
parameter limit suggestions for targets connected to the associated
bus. The max_width field specifies the suggested maximum data
transfer width that should be attempted for data transfers to any
target device connected to the associated bus. The max_reqack_offset
field specifies the maximum number of outstanding REQs that should be
attempted during data transfers to any target device connected to the
associated bus. The max_xfer_rate field specifies the maximum
synchronous ``burst'' data transfer rate that should be attempted for
data transfers to any target device connected to the associated bus.
The SIOC_GET_BUS_LIMITS ioctl indicates the current bus communication
parameter limit suggestions. The max_width, max_reqack_offset and
max_xfer_rate fields only apply to parallel SCSI.
The following is included from <sys/scsi.h>:
/* SCSI communication parameter ioctls */
#define SIOC_GET_LUN_PARMS _IOR('S', 58, struct sioc_lun_parms)
#define SIOC_GET_TGT_PARMS _IOR('S', 59, struct sioc_tgt_parms)
#define SIOC_GET_BUS_PARMS _IOR('S', 60, struct sioc_bus_parms)
#define SIOC_GET_LUN_LIMITS _IOR('S', 61, struct sioc_lun_limits)
#define SIOC_GET_TGT_LIMITS _IOR('S', 62, struct sioc_tgt_limits)
#define SIOC_GET_BUS_LIMITS _IOR('S', 63, struct sioc_bus_limits)
#define SIOC_SET_LUN_LIMITS _IOW('S', 64, struct sioc_lun_limits)
#define SIOC_SET_TGT_LIMITS _IOW('S', 65, struct sioc_tgt_limits)
#define SIOC_SET_BUS_LIMITS _IOW('S', 66, struct sioc_bus_limits)
struct sioc_lun_parms {
unsigned int flags;
unsigned int max_q_depth; /* maximum active I/O's */
unsigned int reserved[4]; /* reserved for future use */
};
struct sioc_lun_limits {
unsigned int flags;
unsigned int max_q_depth;
unsigned int reserved[4]; /* reserved for future use */
};
struct sioc_tgt_parms {
unsigned int flags;
unsigned int width; /* bits */
unsigned int reqack_offset;
unsigned int xfer_rate; /* bytes/sec */
unsigned int reserved[4]; /* reserved for future use */
};
struct sioc_tgt_limits {
unsigned int flags;
unsigned int max_reqack_offset;
unsigned int max_xfer_rate; /* bytes/sec */
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unsigned int max_width; /* bits */
unsigned int reserved[4]; /* reserved for future use */
};
struct sioc_bus_parms {
unsigned int flags; /* reserved for future use */
unsigned int max_width;
unsigned int max_reqack_offset;
unsigned int max_xfer_rate; /* bytes/sec */
unsigned int reserved[4]; /* reserved for future use */
};
struct sioc_bus_limits {
unsigned int flags; /* reserved for future use */
unsigned int max_width;
unsigned int max_reqack_offset;
unsigned int max_xfer_rate; /* bytes/sec */
unsigned int reserved[4]; /* reserved for future use */
};
SCSI Commands and Operations [Toc] [Back]
The SIOC_IO ioctl allows an arbitrary SCSI command to be sent to a
device. All details of the SCSI command protocol are handled
automatically.
The following flags can be used to specify the flags field value:
SCTL_READ Data-in phase expected if the
data_length field is non-zero. The
absence of this flag implies that a
data-out phase is expected if the
data_length field is non-zero.
SCTL_INIT_SDTR synchronous data transfer request
negotiations should be attempted
with this command. This flag only
applies to parallel SCSI.
SCTL_INIT_WDTR wide data transfer request
negotiations should be attempted
with this command. This flag only
applies to parallel SCSI.
SCTL_NO_DISC discpriv bit in Identify message is
not set. This flag only applies to
parallel SCSI.
The cdb field specifies the SCSI command bytes. The number of command
bytes is specified by the cdb_length field. These command bytes are
sent to the target device during the SCSI command phase.
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The address of the data area for the data phase of the SCSI command is
specified by the data field. The data_length field specifies the
maximum number of data bytes to be transferred. A zero-valued
data_length indicates that no data phase should occur. Most SCSI
commands with a data phase expect the data length information to be
included somewhere in the command bytes. The caller is responsible
for correctly specifying both the data_length field and any cdb data
length values. The length may not be larger than SCSI_MAXPHYS and
some implementations further restrict this length.
The max_msecs field specifies the maximum time, in milliseconds, that
the device should need to complete the command. If this period of
time expires without command completion, the system might attempt
recovery procedures to regain the device's attention. These recovery
procedures might include abort tag, abort, and device and bus reset
operations. A zero value in the max_msec field indicates that the
timeout period is infinite and the system should wait indefinitely for
command completion.
When the SIOC_IO ioctl call returns, all command processing has been
completed. Most SIOC_IO ioctl calls will return zero (success). The
resulting detailed ioctl data should be used to evaluate ``success''
or ``failure'' from the caller's perspective. The cdb_status field
indicates the results of the cdb command. If the cdb_status field
indicates a S_CHECK_CONDITION status, the sense_status field indicates
the results of the SCSI REQUEST SENSE command used to collect the
associated sense data. These status fields will contain one of the
following values:
SCTL_INVALID_REQUEST The SCSI command request is invalid and
thus not attempted.
SCTL_SELECT_TIMEOUT The target device does not answer to
selection by the host SCSI interface
(the device does not exist or does not
respond).
SCTL_INCOMPLETE The device answered selection but the
command is not completed (the device
took too long or a communication failure
occurred).
S_GOOD Device successfully completed the
command.
S_CHECK_CONDITION Device indicated sense data is
available.
S_CONDITION_MET Device successfully completed the
command and the requested (search or
pre-fetch) operation is satisfied.
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S_BUSY Device indicated it is unable to accept
the command because it is busy doing
other operations.
S_INTERMEDIATE Device successfully completed this
command, which is one in a series of
linked commands (not supported, see
WARNINGS).
S_I_CONDITION_MET Device indicated both S_INTERMEDIATE and
S_CONDITION_MET (not supported, see
WARNINGS).
S_RESV_CONFLICT Device indicated the command conflicted
with an existing reservation.
S_COMMAND_TERMINATED Device indicated the command is
terminated early by the host system.
S_QUEUE_FULL Device indicated it is unable to accept
the command because its command queue is
currently full.
The data_xfer field indicates the number of data bytes actually
transferred during the data phase of the cdb command. This field is
valid only when the cdb_status field contains one of the following
values: S_GOOD or S_CHECK_CONDITION. The sense_xfer field indicates
the number of valid sense data bytes. This field is valid only when
the cdb_status field contains the value S_CHECK_CONDITION and the
sense_status field contains the value S_GOOD.
The SIOC_ABORT ioctl causes a SCSI ABORT message to be sent to the
LUN. This clears all active commands to the LUN from this initiator.
The SIOC_RESET_DEV ioctl causes a SCSI device to be reset (including
clearing all active commands). On parallel SCSI a SIOC_RESET_DEV
ioctl causes a SCSI BUS DEVICE RESET message to be sent to the
associated target. On Fibre Channel a SIOC_RESET_DEV ioctl causes a
TARGET RESET task management function to be sent to the associated
target followed by a Global Process Logout (GPRLO).
The SIOC_RESET_BUS ioctl causes the system to generate a SCSI bus
reset condition on the associated bus. A SCSI bus reset condition
causes all devices on the bus to be reset (including clearing all
active commands on all devices). The SIOC_RESET_BUS ioctl does not
apply to Fibre Channel.
Often it is necessary or useful to prohibit other SCSI commands while
performing device-control operations. Normally this should be done by
gaining exclusive access via the SIOC_EXCLUSIVE ioctl. The associated
argument points to an integer with one of these values:
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0 release exclusive access to logical unit
1 obtain exclusive access to logical unit
2 release exclusive access to target
3 obtain exclusive access to target
4 release exclusive access to bus
5 obtain exclusive access to bus
Occasionally exclusive access not possible (for example, diagnostic
operations on a device containing a mounted file system). ``Priority
mode'' causes all device-specific driver I/O operations (e.g. file
system I/O and virtual memory page swapping) and all SCSI device
driver open calls (including scsi_ctl open calls) to the associated
LUN to block. These I/O operations and open calls are blocked for the
entire duration that priority mode is in effect. While priority mode
is in effect only SIOC_IO operations should be attempted (these
operations will not be blocked). The SIOC_PRIORITY ioctl controls the
LUN priority mode. This ioctl is only available via the devicecontrol
driver. The value ``1'' enables priority mode. The value
zero disables priority mode.
The header file <sys/scsi.h> has useful information for SCSI device
control. The following is included from <sys/scsi.h>:
/* SCSI device control ioctls */
#define SIOC_IO _IOWR('S', 22, struct sctl_io)
#define SIOC_RESET_DEV _IO('S', 16)
#define SIOC_RESET_BUS _IO('S', 9)
#define SIOC_PRIORITY_MODE _IOW('S', 67, int)
/* Structure for SIOC_IO ioctl */
struct sctl_io
{
unsigned flags;
unsigned char cdb_length;
unsigned char cdb[16];
void *data;
unsigned data_length;
unsigned max_msecs;
unsigned data_xfer;
unsigned cdb_status;
unsigned char sense[256];
unsigned sense_status;
unsigned char sense_xfer;
unsigned char reserved[64];
};
EXAMPLES [Toc] [Back]
Assume that fildes is a valid file descriptor for a SCSI device. The
first example attempts a SCSI INQUIRY command:
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#include <sys/scsi.h>
struct sctl_io sctl_io;
#define MAX_LEN 255
unsigned char inquiry_data[MAX_LEN];
memset(sctl_io, 0, sizeof(sctl_io)); /* clear reserved fields */
sctl_io.flags = SCTL_READ; /* input data expected */
sctl_io.cdb[0] = 0x12; /* can use scsi.h CMDinquiry */
sctl_io.cdb[1] = 0x00;
sctl_io.cdb[2] = 0x00;
sctl_io.cdb[3] = 0x00;
sctl_io.cdb[4] = MAX_LEN; /* allocation length */
sctl_io.cdb[5] = 0x00;
sctl_io.cdb_length = 6; /* 6 byte command */
sctl_io.data = &inquiry_data[0]; /* data buffer location */
sctl_io.data_length = MAX_LEN; /* maximum transfer length */
sctl_io.max_msecs = 10000; /* allow 10 seconds for cmd */
if (ioctl(fildes, SIOC_IO, &sctl_io) < 0)
{
/* request is invalid */
}
The following example attempts a SCSI TEST UNIT READY command and
checks to see if the device is ready, not ready, or in some other
state.
#include <sys/scsi.h>
struct sctl_io sctl_io;
memset(sctl_io, 0, sizeof(sctl_io)); /* clear reserved fields */
sctl_io.flags = 0; /* no data transfer expected */
sctl_io.cdb[0] = 0x00; /* can use CMDtest_unit_ready */
sctl_io.cdb[1] = 0x00;
sctl_io.cdb[2] = 0x00;
sctl_io.cdb[3] = 0x00;
sctl_io.cdb[4] = 0x00;
sctl_io.cdb[5] = 0x00;
sctl_io.cdb_length = 6; /* 6 byte command */
sctl_io.data = NULL; /* no data buffer is provided */
sctl_io.data_length = 0; /* do not transfer data */
sctl_io.max_msecs = 10000; /* allow 10 seconds for cmd */
if (ioctl(fildes, SIOC_IO, &sctl_io) < 0)
{
/* request is invalid */
}
else if (sctl_io.cdb_status == S_GOOD)
{
/* device is ready */
}
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else if (sctl_io.cdb_status == S_BUSY ||
(sctl_io.cdb_status == S_CHECK_CONDITION &&
sctl_io.sense_status == S_GOOD &&
sctl_io.sense_xfer > 2 &&
(sctl_io.sense[2] & 0x0F) == 2)) /* can use sense_data */
{
/* device is not ready */
}
else
{
/* unknown state */
}
WARNINGS [Toc] [Back]
Incorrect use of scsi_ctl operations (even those attempting access to
non-existent devices) can cause data loss, system panics, and device
damage.
The SIOC_EXCLUSIVE ioctl should be used to gain exclusive access to a
device prior to attempting SIOC_IO commands. If exclusive access is
not obtained, SIOC_IO commands will be intermixed with device-specific
driver commands, which can lead to undesirable results.
Device-specific drivers can reject inappropriate or troublesome
SIOC_IO commands. However, since not all such operations are known
and detected, care should be exercised to avoid disrupting devicespecific
drivers when using commands that modify internal device
states.
It is very easy to cause system deadlock through incorrect use of the
SIOC_PRIORITY_MODE ioctl. Normally it is necessary to lock the
calling process into memory (see plock(2)) prior to enabling priority
mode.
Most SCSI commands have a logical unit number (LUN) field. Parallel
SCSI implementations on the HP-UX operating system select logical
units via the SCSI IDENTIFY message. The LUN portion of the cdb
should normally be set to zero, even when the LUN being accessed is
not zero.
Use of linked commands is not supported.
Most SCSI commands with a data phase expect the data length
information to be included somewhere in the command bytes. Both the
data_length field and any cdb data length values must be correctly
specified to get correct command results.
Very large (or infinite) timeout values can cause a parallel SCSI bus
(potentially the entire system) to hang.
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Device and/or bus reset operations can be used to regain a device's
attention when a timeout expires.
Resetting a device can cause I/O errors and/or loss of cached data.
This can result in loss of data and/or system panics.
Obtaining SCSI INQUIRY data by use of the SIOC_INQUIRY ioctl instead
of by use of the SIOC_IO ioctl is generally preferable since SCSI
implementations on the HP-UX operating system synchronize access of
inquiry data during driver open calls.
Since communication parameters can be affected by device-specific
driver capabilities, device-specific driver use might result in
communication parameter changes.
The SIOC_CAPACITY ioctl is not supported by scsi_ctl because the
meaning of capacity is device-specific.
FILES [Toc] [Back]
/usr/include/sys/scsi.h
/usr/include/sys/scsi_ctl.h
SEE ALSO [Toc] [Back]
mknod(1M), ioctl(2), scsi(7).
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