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Technical Reference: Kernel and Subsystems, Volume 2
SSA Disk Concurrent Mode of Operation Interface
The SSA subsystem supports the ability to broadcast
one-byte message codes from one host to all other hosts connected to the same
disk drive. This message-passing capability can be used to synchronize access
to the disk drive. The operating system has a concurrent mode interface to
use this hardware functionality.
The concurrent mode of operation requires that a top
kernel extension runs on all hosts sharing a disk drive. The top kernel extensions
communicate with each other via the SSA subsystem using the concurrent mode
interface of the SSA disk device driver. This interface allows a top kernel
extension to send and receive messages between hosts.
The concurrent mode interface consists of an entry
point in both the SSA disk device driver and the top kernel extension. Two
ioctls register and unregister the top kernel extension with the SSA disk
device driver. The SSA disk device driver's entry point provides the means
to send messages as well as lock, unlock, and test disk drive. The top kernel
extension entry point processes interrupts, including receiving messages from
other hosts.
Note
In order for the concurrent mode interface to work, the node_number attribute of the ssar router must be set to
a different, non zero, value on each of the hosts sharing a disk drive. After
the node_number has been assigned, the host must be
rebooted for it to take effect.
Device Driver Entry Point
The SSA disk device driver concurrent mode entry point
sends commands from the top kernel extension for a specified SSA Disk. The
top kernel extension calls this entry point directly. The DD_CONC_REGISTER ioctl operation registers entry points.
This entry point function takes one argument, which
is a pointer to a conc_cmd structure, that is defined
in the /usr/include/sys/ddconc.h file. The conc_cmd structures must be allocated by the top kernel extension. The
concurrent mode command operation is specified by the cmd_op field in the conc_cmd structure and can
have the following values. For each operation, the devno field of the conc_cmd structure specifies
the appropriate SSA disk drive. The concurrent mode command operation can
have the following values:
Value |
Description |
DD_CONC_SEND_REFRESH |
Broadcasts the one-byte message code specified by the message field of the conc_cmd structure. The code
is sent to all hosts connected to the SSA disk drive. |
DD_CONC_LOCK |
Locks the specified SSA disk drive for this host only. No other hosts
will be able to modify data on the disk drive. |
DD_CONC_UNLOCK |
Unlocks the SSA disk drive. Other hosts can lock and modify data
on the disk drive. |
DD_CONC_TEST |
Issues a test disk command to verify that the SSA disk drive is still
accessible to this host. |
The concurrent mode entry point returns a value of EINVAL if any of the following are true:
- The top kernel extension did not perform
a DD_CONC_REGISTER operation.
- The conc_cmd pointer
is null.
- The devno field
in the conc_cmd structure is invalid.
- The cmd_op field
in the conc_cmd structure is not one of the four valid
values previously listed.
If the concurrent mode entry point accepts the conc_cmd structure, the entry point returns a value of 0.
If the SSA disk device driver does not have resources to issue the command,
the driver queues the command until resources are available. The concurrent
commands queued in the SSA disk device driver are issued before any read or
write operations queued by the driver's strategy entry point.
The completion status of the concurrent mode commands
are returned to the top kernel extension's concurrent mode interrupt handler
entry point.
Top Kernel Extension Entry Point
The top kernel extension must have a concurrent mode
command interrupt handler entry point, which is called directly from the SSA
disk device driver's interrupt handler. This function can take four arguments:
the conc_cmd pointer, and the cmd_op, message_code, and devno fields. The conc_cmd pointer points to a conc_cmd structure. These arguments must be of the same
type specified by the conc_intr_addr function
pointer field in the dd_conc_register structure.
The following valid concurrent mode commands are defined
in the /usr/include/sys/ddcon.h file. For each, the devno field specifies the appropriate SSA disk drive.
Command |
Description |
DD_CONC_SEND_REFRESH |
Indicates the DD_CONC_SEND_REFRESH Device Driver
entry point completed. The error field in the conc_cmd
structure contains the return code necessary for the completion of this command.
The possible values are defined in the /usr/include/sys/errno.h file. The conc_cmd pointer argument to the top
kernel extension's special interrupt handler entry point is non-null. The cmd_op, message_code,
and devno fields are 0. |
DD_CONC_LOCK |
Indicates the DD_CONC_SEND_LOCK device driver
entry point completed. The error field in the conc_cmd
structure contains the return code necessary for the completion of this command.
The possible values are defined in the /usr/include/sys/errno.h file. The conc_cmd pointer argument to the top
kernel extension's special interrupt handler entry point is non-null. The cmd_op, message_code,
and devno fields are zero. |
DD_CONC_UNLOCK |
Indicates the DD_CONC_UNLOCK device driver
entry point completed. The error field in the conc_cmd
structure contains the return code necessary for the completion of this command.
The possible values are defined in the /usr/include/sys/errno.h file. The conc_cmd pointer argument to the top
kernel extension's special interrupt handler entry point is non-null. The cmd_op, message_code,
and devno fields are zero. |
DD_CONC_TEST |
Indicates the DD_CONC_TEST device driver entry
point completed. The error field in the conc_cmd structure
contains the return code necessary for the completion of this command. The
possible values are defined in the /usr/include/sys/errno.h file. The conc_cmd pointer argument to the top
kernel extension's special interrupt handler entry point is non-null. The cmd_op, message_code,
and devno fields are zero. |
DD_CONC_RECV_REFRESH |
Indicates a message with message_code was received
for the SSA disk drive specified by the devno argument.
The conc_cmd argument is null for this operation. |
DD_CONC_RESET |
Indicates the SSA disk drive specified by the devno argument was reset, and all pending messages or commands have been flushed.
The argument conc_cmd is null for this operation. |
- The concurrent command interrupt handler
routine must have a short path length because it runs on the SSA disk device
driver interrupt level. If substantial command processing is needed, then
this routine should schedule an off-level interrupt to its own off-level interrupt
handler.
- The top kernel extension must have an interrupt
priority no higher than the SSA disk device driver's interrupt priority.
- The concurrent command interrupt handler
routine might need to disable interrupts at INTCLASS0 if it is expected to
use concurrent mode on SSA disk drive and some disks of different types. The
other type of disk needs its own device driver to support the concurrent mode.
- A kernel extension that uses the DD_CONC_REGISTER ioctl must issue a DD_CONC_UNREGISTER ioctl before closing the SSA disk drive.
Related Information
The SSA Adapter Device Driver, ssadisk SSA Disk
Device Driver, SSA Subsystem Overview.
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