Providing indirect data addressing for a control block at a channel subsystem of an i/o processing system

FIELD OF INVENTION

0001The present disclosure relates generally to input/output (I/O) processing, and in particular, to providing indirect data addressing for a control block at a channel subsystem of an I/O processing system.

BACKGROUND OF THE INVENTION

0002Input/output (I/O) operations are used to transfer data between memory and I/O devices of an I/O processing system. Specifically, data is written from memory to one or more I/O devices, and data is read from one or more I/O devices to memory by executing I/O operations.

0003To facilitate processing of I/O operations, an I/O subsystem of the I/O processing system is employed. The I/O subsystem is coupled to main memory and the I/O devices of the I/O processing system and directs the flow of information between memory and the I/O devices. One example of an I/O subsystem is a channel subsystem. The channel subsystem uses channel paths as communications media. Each channel path includes a channel coupled to a control unit, the control unit being further coupled to one or more I/O devices.

0004The channel subsystem may employ channel command words (CCWs) to transfer data between the I/O devices and memory. A CCW specifies the I/O command to be executed. For commands initiating certain I/O operations, the CCW designates the memory area associated with the operation, the action to be taken whenever a transfer to or from the area is completed, and other options.

0005During I/O processing, a list of CCWs is fetched from memory by a channel. The channel parses each command from the list of CCWs and forwards a number of the commands, each command in its own entity, to a control unit coupled to the channel. The control unit then processes the commands. The channel tracks the state of each command and controls when the next set of commands are to be sent to the control unit for processing. The channel ensures that each command is sent to the control unit in its own entity. Further, the channel infers certain information associated with processing the response from the control unit for each command.

0006Performing I/O processing on a per CCW basis may involve a large amount of processing overhead for the channel subsystem, as the channels parse CCWs, track state information, and react to responses from the control units. Therefore, it may be beneficial to shift much of the processing burden associated with interpreting and managing CCW and state information from the channel subsystem to the control units. Simplifying the role of channels in communicating between the control units and an operating system in the I/O processing system may increase communication throughput as less handshaking is performed. Simplifying the role of channels in communication may include grouping multiple commands into a single I/O operation. Altering command sequences by grouping two or more commands together in a single I/O operation results in a larger data area required for storing the commands and a data area whose length varies depending on the size and number of commands that are grouped within the single I/O operation.

0007Currently, a single I/O operation can support a single fixed sized command data area that is referenced by a single direct address. This limits the number of commands that can be grouped together in a single I/O operation and thus, limits the increase in throughput that can be gained by grouping commands. In addition, this limits the way that the commands are stored to a contiguous storage area. Performance may be improved by having the commands spread out in a variety of locations. Accordingly, there is a need in the art to be able to store a plurality of commands making up a single I/O operation in non-contiguous storage and for the amount of storage required to be able to vary between different I/O operations.

0008<patcit id="pcit0001" dnum="US7124207B1"><text>US B1 7124207</text></patcit> discloses an apparatus suitable for providing indirect data addressing for a control block at a host computer system.

0009<patcit id="pcit0002" dnum="GB2291990A"><text>GB A 2291990</text></patcit> discloses that direct and indirect addressing modes are well known alternatives.

BRIEF SUMMARY OF THE INVENTION

0010The invention provides a method as claimed in claim 1 and corresponding system and computer program.

BRIEF DESCRIPTION OF THE DRAWINGS

0011The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: <ul id="ul0001" list-style="none"><li><figref idref="f0001">FIG. 1</figref> depicts one embodiment of an I/O processing system incorporating and using one or more aspects of the present invention;</li><li><figref idref="f0002">FIG. 2A</figref> depicts one example of a prior art channel command word;</li><li><figref idref="f0002">FIG. 2B</figref> depicts one example of a prior art channel command word channel program;</li><li><figref idref="f0003">FIG. 3</figref> depicts one embodiment of a prior art link protocol used in communicating between a channel and control unit to execute the channel command word channel program of <figref idref="f0002">FIG. 2B</figref>;</li><li><figref idref="f0004">FIG. 4</figref> depicts one embodiment of a transport control word (TCW) channel program, in accordance with an aspect of the present invention;</li><li><figref idref="f0005">FIG. 5</figref> depicts one embodiment of a link protocol used to communicate between a channel and control unit to execute the TCW channel program of <figref idref="f0004">FIG. 4</figref>, in accordance with an aspect of the present invention;</li><li><figref idref="f0006">FIG. 6</figref> depicts one embodiment of a prior art link protocol used to communicate between a channel and control unit in order to execute four read commands of a channel command word channel program;</li><li><figref idref="f0007">FIG. 7</figref> depicts one embodiment of a link protocol used to communicate between a channel and control unit to process the four read commands of a TCW channel program, in accordance with an aspect of the present invention;</li><li><figref idref="f0008">FIG. 8</figref> depicts one embodiment of a control unit and a channel subsystem, in accordance with an aspect of the present invention;</li><li><figref idref="f0009">FIG. 9</figref> depicts one embodiment of a TCW in accordance with an aspect of the present invention;</li><li><figref idref="f0010">FIG. 10</figref> depicts one embodiment of a TCCB in accordance with an aspect of the present invention;</li><li><figref idref="f0011">FIG. 11</figref> depicts one embodiment of a TCW channel program, in accordance with an aspect of the present invention;</li><li><figref idref="f0012">FIG. 12</figref> depicts one embodiment of a process for providing indirect data addressing for a control block; and</li><li><figref idref="f0013">FIG. 13</figref> depicts one embodiment of an article of manufacture incorporating one or more aspects of the present invention.</li></ul>

0012The detailed description explains the preferred embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.

DETAILED DESCRIPTION OF THE INVENTION

0013In accordance with an aspect of the present invention, input/output (I/O) is facilitated by allowing a plurality of commands making up a single I/O operation to be stored in non-contiguous storage. Depending on factors such as the number of commands and the amount of associated control data, the length of the required storage may vary from one I/O operation to another I/O operation. An exemplary embodiment of the present invention utilizes a list of indirect addresses to gather command data to be sent to a control unit as part of a single I/O operation. This facilitates I/O processing by reducing communications between components of an I/O processing system used to perform the I/O processing. For instance, the number of exchanges and sequences between an I/O communications adapter, such as a channel, and a control unit is reduced. This is accomplished by sending a plurality of commands from the I/O communications adapter to the control unit as a single entity for execution by the control unit.

0014The plurality of commands (e.g., device command words or "DCWs") are included in a block, referred to herein as a transport command control block (TCCB), an address (indirect or direct) of which is specified in a transport control word (TCW). In an exemplary embodiment, the TCW is sent from an operating system (OS) or other application to the I/O communications adapter, which in turn forwards the TCCB in a command message to the control unit for processing. The control unit processes each of the commands absent a tracking of status relative to those individual commands by the I/O communications adapter. The plurality of commands is also referred to as a channel program, which is parsed and executed on the control unit rather than the I/O communications adapter.

0015One example of an I/O processing system incorporating and using one or more aspects of the present invention is described with reference to <figref idref="f0001">FIG. 1</figref>. I/O processing system 100 includes a host system 101, which further includes for instance, a main memory 102, one or more central processing units (CPUs) 104, a storage control element 106, and a channel subsystem 108. The host system 101 may be a large scale computing system, such as a mainframe or server. The I/O processing system 100 also includes one or more control units 110 and one or more I/O devices 112, each of which is described below.

0016Main memory 102 stores data and programs, which can be input from I/O devices 112. For example, the main memory 102 may include one or more operating systems (OSs) 103 that are executed by one or more of the CPUs 104. For example, one CPU 104 can execute a Linux® operating system 103 and a z/OS® operating system 103 as different virtual machine instances. The main memory 102 is directly addressable and provides for high-speed processing of data by the CPUs 104 and the channel subsystem 108.

0017CPU 104 is the controlling center of the I/O processing system 100. It contains sequencing and processing facilities for instruction execution, interruption action, timing functions, initial program loading, and other machine-related functions. CPU 104 is coupled to the storage control element 106 via a connection 114, such as a bidirectional or unidirectional bus.

0018Storage control element 106 is coupled to the main memory 102 via a connection 116, such as a bus; to CPUs 104 via connection 114; and to channel subsystem 108 via a connection 118. Storage control element 106 controls, for example, queuing and execution of requests made by one or more of the CPU 104 and the channel subsystem 108.

0019In an exemplary embodiment, channel subsystem 108 provides a communication interface between host system 101 and control units 110. Channel subsystem 108 is coupled to storage control element 106, as described above, and to each of the control units 110 via a connection 120, such as a serial link. Connection 120 may be implemented in any manner known in the art, including an optical link, employing single-mode or multi-mode waveguides in a Fibre Channel fabric (e.g., a fibre channel network). Channel subsystem 108 directs the flow of information between I/O devices 112 and main memory 102. It relieves the CPUs 104 of the task of communicating directly with the I/O devices 112 and permits data processing to proceed concurrently with I/O processing. The channel subsystem 108 uses one or more channel paths 122 as the communication links in managing the flow of information to or from I/O devices 112. As a part of the I/O processing, channel subsystem 108 also performs the path-management functions of testing for channel path availability, selecting an available channel path 122 and initiating execution of the operation with the I/O devices 112.

0020Each channel path 122 includes a channel 124 (channels 124 are located within the channel subsystem 108, in one example, as shown in <figref idref="f0001">FIG. 1</figref>), one or more control units 110 and one or more connections 120. In another example, it is also possible to have one or more dynamic switches (not depicted) as part of the channel path 122. A dynamic switch may be coupled to a channel 124 and a control unit 110 and provides the capability of physically interconnecting any two links that are attached to the switch. In another example, it is also possible to have multiple systems, and therefore multiple channel subsystems (not depicted) attached to one or more of the control units 110.

0021Also located within channel subsystem 108 are subchannels (not shown). One subchannel is provided for and dedicated to each I/O device 112 accessible to a program through the channel subsystem 108. A subchannel (e.g., a data structure, such as a table) provides the logical appearance of a device to the program. Each subchannel provides information concerning the associated I/O device 112 and its attachment to channel subsystem 108. The subchannel also provides information concerning I/O operations and other functions involving the associated I/O device 112. The subchannel is the means by which channel subsystem 108 provides information about associated I/O devices 112 to CPUs 104, which obtain this information by executing I/O instructions.

0022Channel subsystem 108 is coupled to one or more control units 110. Each control unit 110 provides logic to operate and control one or more I/O devices 112 and adapts, through the use of common facilities, the characteristics of each I/O device 112 to the link interface provided by the channel 124. The common facilities provide for the execution of I/O operations, indications concerning the status of the I/O device 112 and control unit 110, control of the timing of data transfers over the channel path 122 and certain levels of I/O device 112 control.

0023Each control unit 110 is attached via a connection 126 (e.g., a bus) to one or more I/O devices 112. I/O devices 112 receive information or store information in main memory 102 and/or other memory. Examples of I/O devices 112 include card readers and punches, magnetic tape units, direct access storage devices, displays, keyboards, printers, pointing devices, teleprocessing devices, communication controllers and sensor based equipment, to name a few.

0024One or more of the above components of the I/O processing system 100 are further described in "<nplcit id="ncit0001" npl-type="b"><text>IBM® z/Architecture Principles of Operation," Publication No. SA22-7832-05, 6th Edition, April 2007</text></nplcit>; <patcit id="pcit0003" dnum="US5461721A"><text>U.S. Patent No. 5,461,721</text></patcit> entitled "System For Transferring Data Between I/O Devices And Main Or Expanded Storage Under Dynamic Control Of Independent Indirect Address Words (IDAWS)," Cormier et al., issued October 24, 1995; and <patcit id="pcit0004" dnum="US5526484A"><text>U.S. Patent No. 5,526,484</text></patcit> entitled "Method And System For Pipelining The Processing Of Channel Command Words," Casper et al., issued June 11, 1996. IBM is a registered trademark of International Business Machines Corporation, Armonk, New York, USA. Other names used herein may be registered trademarks, trademarks or product names of International Business Machines Corporation or other companies.

0025In one embodiment, to transfer data between I/O devices 112 and memory 102, channel command words (CCWs) are used. A CCW specifies the command to be executed, and includes other fields to control processing. One example of a CCW is described with reference to <figref idref="f0002">FIG. 2A</figref>. A CCW 200 includes, for example, a command code 202 specifying the command to be executed (e.g., read, read backward, control, sense and write); a plurality of flags 204 used to control the I/O operation; for commands that specify the transfer of data, a count field 206 that specifies the number of bytes in the storage area designated by the CCW 200 to be transferred; and a data address 208 that points to a location in main memory that includes the data, when direct addressing is employed, or to a list (e.g., contiguous list) of modified indirect data address words (MIDAWs) to be processed, when modified indirect data addressing is employed. Modified indirect addressing is further described in <patcit id="pcit0005" dnum="US20080043563A" dnum-type="L"><text>U.S. Published Patent Application Number 2008/0043563</text></patcit>, entitled "Flexibly Controlling The Transfer Of Data Between Input/Output Devices And Memory," Brice et al., filed August 15, 2006.

0026One or more CCWs arranged for sequential execution form a channel program, also referred to herein as a CCW channel program. The CCW channel program is set up by, for example, an operating system, or other software. The software sets up the CCWs and obtains the addresses of memory assigned to the channel program. An example of a CCW channel program is described with reference to <figref idref="f0002">FIG. 2B</figref>. A CCW channel program 210 includes, for instance, a define extent CCW 212 that has a pointer 214 to a location in memory of define extent data 216 to be used with the define extent command. In this example, a transfer in channel (TIC) 218 follows the define extent command that refers the channel program to another area in memory (e.g., an application area) that includes one or more other CCWs, such as a locate record 217 that has a pointer 219 to locate record data 220, and one or more read CCWs 221. Each read CCW 221 has a pointer 222 to a data area 224. The data area includes an address to directly access the data or a list of data address words (e.g., MIDAWs or IDAWs) to indirectly access the data. Further, CCW channel program 210 includes a predetermined area in the channel subsystem defined by the device address called the subchannel for status 226 resulting from execution of the CCW channel program.

0027The processing of a CCW channel program is described with reference to <figref idref="f0003">FIG. 3</figref>, as well as with reference to <figref idref="f0002">FIG. 2B</figref>. In particular, <figref idref="f0003">FIG. 3</figref> shows an example of the various exchanges and sequences that occur between a channel and a control unit when a CCW channel program is executing. The link protocol used for the communications is FICON (Fibre Connectivity), in this example. Information regarding FICON is described in "<nplcit id="ncit0002" npl-type="s"><text>Fibre Channel Single Byte Command Code Sets-3 Mapping Protocol" (FC-SB-3), T11/Project 1357-D/Rev. 1.6, INCITS (March 2003</text></nplcit>).

0028Referring to <figref idref="f0003">FIG. 3</figref>, a channel 300 opens an exchange with a control unit 302 and sends a define extent command and data associated therewith 304 to control unit 302. The command is fetched from define extent CCW 212 (<figref idref="f0002">FIG. 2B</figref>) and the data is obtained from define extent data area 216. The channel 300 uses TIC 218 to locate the locate record CCW and the read CCW. It fetches the locate record command 305 (<figref idref="f0003">FIG. 3</figref>) from the locate record CCW 217 (<figref idref="f0002">FIG. 2B</figref>) and obtains the data from locate record data 220. The read command 306 (<figref idref="f0003">FIG. 3</figref>) is fetched from read CCW 221 (<figref idref="f0002">FIG. 2B</figref>). Each is sent to the control unit 302.

0029The control unit 302 opens an exchange 308 with the channel 300, in response to the open exchange of the channel 300. This can occur before or after locate command 305 and/or read command 306. Along with the open exchange, a response (CMR) is forwarded to the channel 300. The CMR provides an indication to the channel 300 that the control unit 302 is active and operating.

0030The control unit 302 sends the requested data 310 to the channel 300. Additionally, the control unit 302 provides the status to the channel 300 and closes the exchange 312. In response thereto, the channel 300 stores the data, examines the status and closes the exchange 314, which indicates to the control unit 302 that the status has been received.

0031The processing of the above CCW channel program to read 4k of data requires two exchanges to be opened and closed and seven sequences. The total number of exchanges and sequences between the channel and control unit is reduced through collapsing multiple commands of the channel program into a TCCB. The channel, e.g., channel 124 of <figref idref="f0001">FIG. 1</figref>, uses a TCW to identify the location of the TCCB, as well as locations for accessing and storing status and data associated with executing the channel program. The TCW is interpreted by the channel 124 and is not sent or seen by the control unit 110.

0032One example of a channel program to read 4k of data, as in <figref idref="f0002">FIG. 2B</figref>, but includes a TCCB, instead of separate individual CCWs, is described with reference to <figref idref="f0004">FIG. 4</figref>. As shown, a channel program 400, referred to herein as a TCW channel program, includes a TCW 402 specifying a location in memory of a TCCB 404, as well as a location in memory of a data area 406 or a TIDAL 410 (i.e., a list of transport mode indirect data address words (TIDAWs), similar to MIDAWs) that points to data area 406, and a status area 408.

0033The processing of a TCW channel program is described with reference to <figref idref="f0005">FIG. 5</figref>. The link protocol used for these communications is, for instance, Fibre Channel Protocol (FCP). In particular, three phases of the FCP link protocol are used, allowing host bus adapters to be used that support FCP to perform data transfers controlled by CCWs. FCP and its phases are described further in "<nplcit id="ncit0003" npl-type="s"><text>Information Technology - Fibre Channel Protocol for SCSI, Third Version (FCP-3)," T10 Project 1560-D, Revision 4, September 13, 2005</text></nplcit>.

0034Referring to <figref idref="f0005">FIG. 5</figref>, a channel 500 opens an exchange with a control unit 502 and sends TCCB 504 to the control unit 502. In one example, the TCCB 504 and sequence initiative are transferred to the control unit 502 in a FCP command, referred to as FCP_CMND information unit (IU) or a transport command IU. The control unit 502 executes the multiple commands of the TCCB 504 (e.g., define extent command, locate record command, read command as device control words (DCWs)) and forwards data 506 to the channel 500 via, for instance, a FCP_Data IU. It also provides status and closes the exchange 508. As one example, final status is sent in a FCP status frame that has a bit active in, for instance, byte 10 or 11 of the payload of a FCP_RSP IU, also referred to as a transport response IU. The FCP_RSP_IU payload may be used to transport FICON ending status along with additional status information.

0035In a further example, to write 4k of customer data, the channel 500 uses the FCP link protocol phases, as follows: <ol id="ol0001"><li>1. Transfer a TCCB in the FCP_CMND IU.</li><li>2. Transfer the IU of data, and sequence initiative to the control unit 502. (FCP Transfer Ready Disabled)</li><li>3. Final status is sent in a FCP status frame that has a bit active in, for instance, byte 10 or 11 of the FCP_RSP IU Payload. The FCP_RES_INFO field or sense field is used to transport FICON ending status along with additional status information.</li></ol>

0036By executing the TCW channel program of <figref idref="f0004">FIG. 4</figref>, there is only one exchange opened and closed (see also <figref idref="f0005">FIG. 5</figref>), instead of two exchanges for the CCW channel program of <figref idref="f0002">FIG. 2B</figref> (see also <figref idref="f0003">FIG. 3</figref>). Further, for the TCW channel program, there are three communication sequences (see <figref idref="f0004 f0005">FIGs. 4-5</figref>), as compared to seven sequences for the CCW channel program (see <figref idref="f0002 f0003">FIGs. 2B-3</figref>).

0037The number of exchanges and sequences remain the same for a TCW channel program, even if additional commands are added to the program. Compare, for example, the communications of the CCW channel program of <figref idref="f0006">FIG. 6</figref> with the communications of the TCW channel program of <figref idref="f0007">FIG. 7</figref>. In the CCW channel program of <figref idref="f0006">FIG. 6</figref>, each of the commands (e.g., define extent command 600, locate record command 601, read command 602, read command 604, read command 606, locate record command 607 and read command 608) are sent in separate sequences from channel 610 to control unit 612. Further, each 4k block of data (e.g., data 614-620) is sent in separate sequences from the control unit 612 to the channel 610. This CCW channel program requires two exchanges to be opened and closed (e.g., open exchanges 622, 624 and close exchanges 626, 628), and fourteen communications sequences. This is compared to the three sequences and one exchange for the TCW channel program of <figref idref="f0007">FIG. 7</figref>, which accomplishes the same task as the CCW channel program of <figref idref="f0006">FIG. 6</figref>.

0038As depicted in <figref idref="f0007">FIG. 7</figref>, a channel 700 opens an exchange with a control unit 702 and sends a TCCB 704 to the control unit 702. The TCCB 704 includes the define extent command, the two locate record commands, and the four read commands in DCWs, as described above. In response to receiving the TCCB 704, the control unit 702 executes the commands and sends, in a single sequence, the 16k of data 706 to the channel 700. Additionally, the control unit 702 provides status to the channel 700 and closes the exchange 708. Thus, the TCW channel program requires much fewer communications to transfer the same amount of data as the CCW channel program of <figref idref="f0006">FIG. 6</figref>.

0039Turning now to <figref idref="f0008">FIG. 8</figref>, one embodiment of channel 124 in the channel subsystem 108 and the control unit 110 of <figref idref="f0001">FIG. 1</figref> that support TCW channel program execution are depicted in greater detail. The control unit 110 includes CU control logic 802 to parse and process command messages containing a TCCB, such as the TCCB 704 of <figref idref="f0007">FIG. 7</figref>, received from the channel 124 via the connection 120. The CU control logic 802 can extract DCWs and control data from the TCCB received at the control unit 110 to control a device, for instance, I/O device 112 via connection 126. The CU control logic 802 sends device commands and data to the I/O device 112 and receives status information and other feedback from the I/O device 112. For example, the I/O device 112 may be busy because of a previous reservation request targeting I/O device 112. To manage potential device reservation contention issues that can arise when the control unit 110 receives multiple requests to access the same I/O device 112, the CU control logic 802 keeps track of and stores device busy messages and associated data in a device busy queue 804.

0040The control unit 110 may further include other buffer or memory elements (not depicted) to store multiple messages or status information associated with communications between the channel 124 and the I/O device 112. For example, a register located on the control unit 110 may include a maximum control unit exchange parameter that defines the maximum number of open control unit exchanges that the control unit 110 supports.

0041The channel 124 in the channel subsystem 108 includes elements to support communication with the control unit 110. In an exemplary embodiment, the CHN control logic 806 controls communication between the channel subsystem 108 and the control unit 110. The CHN control logic 806 may directly interface to the CU control logic 802 via the connection 120 to send commands and receive responses, such as transport command and response IUs. Alternatively, messaging interfaces and/or buffers (not depicted) can be placed between the CHN control logic 806 and the CU control logic 802.

0042An exemplary embodiment of a transport control word (TCW) 900 is depicted in <figref idref="f0009">FIG. 9</figref>. The TCW 900 is utilized by the channel 124 to set up the I/O operation and is not sent to the control unit 110. The TCW depicted in <figref idref="f0009">FIG. 9</figref> provides for indirect addressing of a TCCB by utilizing a TCCB TIDAL flag and a TCCB address.

0043In an exemplary TCW 900 depicted in <figref idref="f0009">FIG. 9</figref>, a format field 902 equal to "00b" indicates that what follows is a TCW 900. The TCW 900 also includes reserved bits 904 for possible future use.

0044The TCW 900 also includes a flags field 906. The first five bits of the flags field 906 are reserved for future use and are set to zero. The sixth bit of the flags field 906 is a TIDAL read flag. In an exemplary embodiment, the TIDAL read flag is set (e.g., to one) when the input-data address field 918 contains an address of a TIDAL. If the TIDAL read flag is reset (e.g., to zero), then the input-data address field 918 contains a data address. The seventh bit of the flags field 906 is the TCCB TIDAL flag. In an exemplary embodiment, the TCCB TIDAL flag is set to one when the TCCB address field 922 contains an address of a TIDAL. If the TCCB TIDAL flag is set to zero, then the TCCB address field 922 directly addresses the TCCB. The TCCB TIDAL flag allows the operating system software or the hyper-visor to layer function and prefix user channel programs. The eighth bit of the flags field 906 is a TIDAL write flag. In an exemplary embodiment, the TIDAL write flag is set to one when the output-data address field 916 contains an address of a TIDAL. If the TIDAL write flag is set to zero, then the output-data address field 916 contains a data address.

0045The ninth through twenty-forth bits of the flags field 906 is reserved for future use.

0046The TCW 900 also includes a TCCB length field 910 which indirectly represents the length of the TCCB and may be utilized to determine the actual length of the TCCB.

0047The read/write bits 912 in the TCW 900 are utilized to indicate whether data is being read and/or written as a result of executing the TCW 900. In an exemplary embodiment, the read bit in the read/write 912 bits is set to one to indicate that input data is being transferred from an I/O device 112 to system storage (e.g., main memory 102) in the host system 101 as a result of executing the TCW 900. The write bit in the read/write bits 912 is set to one to indicate that output data is being transferred from system storage (e.g., main memory 102) in the host system 101 to an I/O device as a result of executing the TCW 900.

0048The output-data address field 916 includes the address for the output data (if any). As described previously, the contents of the output-data address field 916 may be an address of a TIDAL for output data or the actual address of the output data. The input-data address field 918 includes the address for the input data (if any). As described previously, the contents of the input-data address field 918 may be an address of a TIDAL for input data or the actual address of the input data. In an exemplary embodiment, the output-data address field 916 and the input data address field 918 are implemented as sixty-four bit addresses.

0049The TCW 900 also includes a transport-status-block address field 920. A portion (e.g., the extended status part) of a completion status in a transport response IU for an I/O operation is stored at this address. The TCCB address field 922 in the TCW 900 includes an address where the TCCB is located in system storage. As described previously, the TCCB is the control block where the DCWs to be executed for the TCW 900 reside. Also as described previously, the contents of the TCCB address field 922 may be an address of a TIDAL for the TCCB or the actual address of the TCCB. In an exemplary embodiment, the transport-status-block address field 920 and the TCCB address field 922 are implemented as sixty-four bit addresses.

0050The output count field 924 in the TCW 900 indicates the amount of output data to be transferred by the TCW/TCCB for an output operation. In an exemplary embodiment, the output count field 924 specifies the number of bytes in the output storage area designed by the TCW (the output-data address 916) to be transferred. The input count field 926 in the TCW 900 indicates the amount of input data to be transferred by the TCW/TCCB for an input operation. In an exemplary embodiment, the input count field 926 specifies the number of bytes in the input storage area designed by the TCW (the input-data address 918) to be transferred. Several additional fields in the TCW 900 are reserved: reserved field 928, reserved field 930 and reserved field 932. The interrogate-TCW address field 934 contains the address of another TCW and is used by the channel 124 to interrogate that state of an operation under the initiative of a cancel sub-channel I/O instruction.

0051The TCW depicted in <figref idref="f0009">FIG. 9</figref> is one example of how a command word can be configured. Other configurations are possible where additional fields are included and/or fields depicted in <figref idref="f0009">FIG. 9</figref> are not included.

0052<figref idref="f0010">FIG. 10</figref> depicts one embodiment of a TCCB 1000 in accordance with an aspect of the present invention. The TCCB 1000 in <figref idref="f0010">FIG. 10</figref> is located at the address indicated in the TCCB address field 922 in the TCW 900. This address may be a direct address or an indirect address, allowing the contents of the TCCB 1000 to be in one storage location or to be spread among multiple non-contiguous storage locations. As described previously, the TCCB 1000 is a control block built by software and then the channel 124 sends it to a control unit 110 (e.g., in a Transport Command_IU) for execution. The TCCB 1000 contains the commands to be executed by the control unit 110 and any control data required by the commands. The channel 124 does not look at the contents of the TCCB 1000. The channel 124 packages the TCCB 1000 and sends it to the control unit 110. This allows FCP transport protocols to be utilized instead of FICON.

0053The TCCB 1000 includes a transport control area header (TCAH) 1002 which, in an exemplary embodiment, includes information about the transmit control area (TCA) 1004 and operations within the TCA 1004 (e.g., length, service code). In an exemplary embodiment the TCAH 1002 includes a format control field for specifying information such as the format of the TCCB (e.g., variable length CDB format), the mode associated with the TCCB (e.g., transport mode), service action codes set aside to be used as vendor unique code points, and a field to provide the control unit the priority in which to execute this TCCB 1000.

0054The TCCB 1000 depicted in <figref idref="f0010">FIG. 10</figref> also includes a variable length TCA 1004 which includes one or more DCWs 1006 and corresponding DCW control data 1008, if any for each DCW 1006. The DCW control data 1008 may be of variable length. In an exemplary embodiment, each DCW 1006 includes a command code, flags (chaining), control data length, and read/write data length. DCW control data 1008 is optional (depending on the DCW 1006) and includes control parameters for its corresponding DCW 1006. For example, DCW control data 1008 may include define extent and/or prefix parameters. In an exemplary embodiment, the DCW control data 1008 follows its corresponding DCW 1006 within the TCA 1004 and is not pointed to by the DCW 1006.

0055In addition, the TCCB 1000 includes a TCA trailer (TCAT) 1010 that contains data such as the count of the bytes to be transferred in the TCCB 1000 and a check word field to check the integrity of the TCCB 1000.

0056<figref idref="f0011">FIG. 11</figref> depicts one embodiment of a TCW channel program 1100, in accordance with an aspect of the present invention. As shown in <figref idref="f0011">FIG. 11</figref>, the TCW channel program 1100 includes a TCW 1102 specifying a location in memory of a TCCB 1104 or TIDAL 1112 (i.e., a list of transport indirect data address words (TIDAWs)) that points to the location for the TCCB 1104. In addition, the example channel program 1100 depicted in <figref idref="f0011">FIG. 11</figref> includes a location in memory of an input data area 1106 or a TIDAL 1110 that points to the input data area 1106, and a status area 1108.

0057<figref idref="f0012">FIG. 12</figref> depicts one embodiment of a process for providing indirect data addressing for a control block (e.g., a TCCB) in accordance with an aspect of the present invention. In an exemplary embodiment, the processing depicted in <figref idref="f0012">FIG. 12</figref> occurs at a host computer system that is in network communication with a control unit. The host computer system may include an I/O processing system that executes the process. Additionally, the I/O processing system may include channel subsystem that executes the process. At block 1202, a TCW is obtained by the host computer. In an exemplary embodiment, the TCW is obtained (or received) from an operating system running on the host computer. The TCW includes a TCCB address 922 and a TCCB TIDAL flag located in the flags field 906. At block 1204, the TCCB address 922 and TCCB TIDAL flags are extracted from the TCW.

0058At block 1206, it is determined if the TCCB TIDAL flag is set. If the TCCB TIDAL flag is set, then the TCCB address 922 is an indirect data address and processing continues at block 1210. At block 1210, the TCCB is gathered from the location specified by the TCW. Because the address is an indirect address, the TCCB address 922 includes an address of a TIDAL. The TIDAL includes a list of addresses that point to a plurality of storage locations that collectively make up the TCCB. Processing then continues at block 1212.

0059If the TCCB TIDAL flag is not set, as determined at block 1206, then the TCCB address 922 is a direct data address and processing continues at block 1208. At block 1208, the TCCB is gathered from the location specified by the TCW. Because the address is a direct address, the TCCB is located at the address specified by the TCCB address 922. Processing then continues at block 1212.

0060At block 1212, the I/O operation, including the TCCB is forwarded to a control unit for execution.

0061Technical effects of exemplary embodiments include the ability to spread the TCCB among non-contiguous storage locations. This may lead to performance improvements due to the ability to easily add on to contents of the TCCB and due to reduced contention for particular storage locations. Technical effects also include the ability to have a variable length TCCB which allows for flexibility in grouping commands together for transmission to a control unit.

0062As described above, embodiments can be embodied in the form of computer-implemented processes and apparatuses for practicing those processes. In exemplary embodiments, the invention is embodied in computer program code executed by one or more network elements. Embodiments include a computer program product 1300 as depicted in <figref idref="f0013">FIG. 13</figref> on a computer usable medium 1302 with computer program code logic 1304 containing instructions embodied in tangible media as an article of manufacture. Exemplary articles of manufacture for computer usable medium 1302 may include floppy diskettes, CD-ROMs, hard drives, universal serial bus (USB) flash drives, or any other computer-readable storage medium, wherein, when the computer program code logic 1304 is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. Embodiments include computer program code logic 1304, for example, whether stored in a storage medium, loaded into and/or executed by a computer, or transmitted over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein, when the computer program code logic 1304 is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. When implemented on a general-purpose microprocessor, the computer program code logic 1304 segments configure the microprocessor to create specific logic circuits.