I/o authorization control in shared storage systems

BACKGROUND

Field of the Invention

0001This invention relates to systems and methods for controlling I/O authorization in storage systems.

Background of the Invention

0002As network environments and storage-area-networks grow in usage and popularity, an increasing number of subscribers and applications share connectivity to storage devices and volumes (physical or logical). Utilizing shared storage typically simplifies management and enables a single logical resource to be used by multiple subscribers or applications. It also typically reduces the underutilization of storage resources. This is because different systems or application may require less storage than others, and sharing storage allows the different systems or application to use the amount of storage they need without wasting or underutilizing storage. As needs change, more or less storage may be allocated to the shared storage environment, thereby simplifying the scaling of storage resources.

0003Despite its advantages, shared storage is not without drawbacks. For example, shared storage may lead to resource contention as multiple systems or applications attempt to access the shared storage. Shared storage may also give rise to different security issues. Because multiple systems or applications may access the same storage, potential arises for certain systems or applications to access data or storage space that is only intended for or authorized to be used by other systems or applications. Although different security products may be available to limit access to certain data, these security products typically don't protect data at the volume level. As a result, programs such as I/O channel programs may be used to directly access data sets outside of normal access methods and security procedures. For example, a program may be written with a STARTIO instruction to issue READ commands to access data that should be within protected datasets, or WRITE commands to corrupt the same data.

0004In view of the foregoing, what are needed are systems and methods to add an additional layer of security to shared storage and decrease the potential that shared data or volumes will be accessed in an unauthorized manner.

SUMMARY

0005The invention has been developed in response to the present state of the art and, in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available systems and methods. Accordingly, the invention has been developed to provide improved systems and methods for limiting I/O access in shared storage systems. The features and advantages of the invention will become more fully apparent from the following description and appended claims, or may be learned by practice of the invention as set forth hereinafter.

0006Consistent with the foregoing, a method for limiting I/O access in shared storage systems is disclosed. In one embodiment, such a method includes establishing, for a volume, a list of address spaces that are authorized to access the volume. The method further receives an I/O request to access the volume and determines whether the I/O request originates from one of the address spaces identified in the list. If the I/O request originates from one of the address spaces in the list, the method passes the I/O request to the volume. If, on the other hand, the I/O request does not originate from one of the address spaces in the list, the method blocks the I/O request. A corresponding system and computer program product are also disclosed and claimed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered limiting of its scope, the embodiments of the invention will be described and explained with additional specificity and detail through use of the accompanying drawings, in which:

<figref idref="DRAWINGS">FIG. 1</figref> is a high-level block diagram showing one example of a network environment in which systems and methods in accordance with the invention may operate;

<figref idref="DRAWINGS">FIG. 2</figref> is a high-level block diagram showing one example of a storage system for use in the network environment of <figref idref="DRAWINGS">FIG. 1</figref>;

<figref idref="DRAWINGS">FIG. 3</figref> is a high-level block diagram showing an I/O authorization control module configured to limit I/O access in a shared storage system;

<figref idref="DRAWINGS">FIG. 4</figref> is a process flow diagram showing a generalized method for limiting I/O access in a shared storage system;

<figref idref="DRAWINGS">FIG. 5</figref> is a high-level block diagram showing various control blocks and data structures in an exemplary implementation for limiting I/O access in a shared storage system; and

<figref idref="DRAWINGS">FIG. 6</figref> is a process flow diagram showing a more specific exemplary method for limiting I/O access in a shared storage system.

DETAILED DESCRIPTION

0014It will be readily understood that the components of the present invention, as generally described and illustrated in the Figures herein, could be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the invention, as represented in the Figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of certain examples of presently contemplated embodiments in accordance with the invention. The presently described embodiments will be best understood by reference to the drawings, wherein like parts are designated by like numerals throughout.

0015The present invention may be embodied as a system, method, and/or computer program product. The computer program product may include a computer readable storage medium (or media) having computer readable program instructions thereon for causing a processor to carry out aspects of the present invention.

0016The computer readable storage medium may be a tangible device that can retain and store instructions for use by an instruction execution device. The computer readable storage medium may be, for example, but is not limited to, an electronic storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination of the foregoing. A non-exhaustive list of more specific examples of the computer readable storage medium includes the following: a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanically encoded device such as punch-cards or raised structures in a groove having instructions recorded thereon, and any suitable combination of the foregoing. A computer readable storage medium, as used herein, is not to be construed as being transitory signals per se, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through a waveguide or other transmission media (e.g., light pulses passing through a fiber-optic cable), or electrical signals transmitted through a wire.

0017Computer readable program instructions described herein can be downloaded to respective computing/processing devices from a computer readable storage medium or to an external computer or external storage device via a network, for example, the Internet, a local area network, a wide area network and/or a wireless network. The network may comprise copper transmission cables, optical transmission fibers, wireless transmission, routers, firewalls, switches, gateway computers and/or edge servers. A network adapter card or network interface in each computing/processing device receives computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium within the respective computing/processing device.

0018Computer readable program instructions for carrying out operations of the present invention may be assembler instructions, instruction-set-architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state-setting data, or either source code or object code written in any combination of one or more programming languages, including an object oriented programming language such as Smalltalk, C++ or the like, and conventional procedural programming languages, such as the “C” programming language or similar programming languages.

0019The computer readable program instructions may execute entirely on a user's computer, partly on a user's computer, as a stand-alone software package, partly on a user's computer and partly on a remote computer, or entirely on a remote computer or server. In the latter scenario, a remote computer may be connected to a user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate arrays (FPGA), or programmable logic arrays (PLA) may execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present invention.

0020Aspects of the present invention are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, may be implemented by computer readable program instructions.

0021These computer readable program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks. These computer readable program instructions may also be stored in a computer readable storage medium that can direct a computer, a programmable data processing apparatus, and/or other devices to function in a particular manner, such that the computer readable storage medium having instructions stored therein comprises an article of manufacture including instructions which implement aspects of the function/act specified in the flowchart and/or block diagram block or blocks.

0022The computer readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device to cause a series of operational steps to be performed on the computer, other programmable apparatus, or other device to produce a computer implemented process, such that the instructions which execute on the computer, other programmable apparatus, or other device implement the functions/acts specified in the flowchart and/or block diagram block or blocks.

0023Referring to <figref idref="DRAWINGS">FIG. 1</figref>, one example of a network environment <b>100</b> is illustrated. The network environment <b>100</b> is presented to show one example of an environment where systems and methods in accordance with the invention may be implemented. The network environment <b>100</b> is presented only by way of example and not limitation. Indeed, the systems and methods disclosed herein may be applicable to a wide variety of network environments, in addition to the network environment <b>100</b> shown.

0024As shown, the network environment <b>100</b> includes one or more computers <b>102</b>, <b>106</b> interconnected by a network <b>104</b>. The network <b>104</b> may include, for example, a local-area-network (LAN) <b>104</b>, a wide-area-network (WAN) <b>104</b>, the Internet <b>104</b>, an intranet <b>104</b>, or the like. In certain embodiments, the computers <b>102</b>, <b>106</b> may include both client computers <b>102</b> and server computers <b>106</b> (also referred to herein as “host systems” <b>106</b>). In general, the client computers <b>102</b> initiate communication sessions, whereas the server computers <b>106</b> wait for requests from the client computers <b>102</b>. In certain embodiments, the computers <b>102</b> and/or servers <b>106</b> may connect to one or more internal or external direct-attached storage systems <b>109</b> (e.g., arrays of hard-disk drives, solid-state drives, tape drives, etc.). These computers <b>102</b>, <b>106</b> and direct-attached storage systems <b>109</b> may communicate using protocols such as ATA, SATA, SCSI, SAS, Fibre Channel, or the like.

0025The network environment <b>100</b> may, in certain embodiments, include a storage network <b>108</b> behind the servers <b>106</b>, such as a storage-area-network (SAN) <b>108</b> or a LAN <b>108</b> (e.g., when using network-attached storage). This network <b>108</b> may connect the servers <b>106</b> to one or more storage systems, such as arrays <b>110</b> of hard-disk drives or solid-state drives, tape libraries <b>112</b>, individual hard-disk drives <b>114</b> or solid-state drives <b>114</b>, tape drives <b>116</b>, CD-ROM libraries, or the like. To access a storage system <b>110</b>, <b>112</b>, <b>114</b>, <b>116</b>, a host system <b>106</b> may communicate over physical connections from one or more ports on the host <b>106</b> to one or more ports on the storage system <b>110</b>, <b>112</b>, <b>114</b>, <b>116</b>. A connection may be through a switch, fabric, direct connection, or the like. In certain embodiments, the servers <b>106</b> and storage systems <b>110</b>, <b>112</b>, <b>114</b>, <b>116</b> may communicate using a networking standard such as Fibre Channel (FC).

0026Referring to <figref idref="DRAWINGS">FIG. 2</figref>, one embodiment of a storage system <b>110</b> containing an array of hard-disk drives <b>204</b> and/or solid-state drives <b>204</b> is illustrated. As shown, the storage system <b>110</b> includes a storage controller <b>200</b>, one or more switches <b>202</b>, and one or more storage drives <b>204</b>, such as hard disk drives <b>204</b> or solid-state drives <b>204</b> (such as flash-memory-based drives <b>204</b>). The storage controller <b>200</b> may enable one or more hosts <b>106</b> (e.g., open system and/or mainframe servers <b>106</b> running operating systems such z/OS, zVM, or the like) to access data in the one or more storage drives <b>204</b>.

0027In selected embodiments, the storage controller <b>200</b> includes one or more servers <b>206</b>. The storage controller <b>200</b> may also include host adapters <b>208</b> and device adapters <b>210</b> to connect the storage controller <b>200</b> to host devices <b>106</b> and storage drives <b>204</b>, respectively. Multiple servers <b>206</b><i>a</i>, <b>206</b><i>b </i>may provide redundancy to ensure that data is always available to connected hosts <b>106</b>. Thus, when one server <b>206</b><i>a </i>fails, the other server <b>206</b><i>b </i>may pick up the I/O load of the failed server <b>206</b><i>a </i>to ensure that I/O is able to continue between the hosts <b>106</b> and the storage drives <b>204</b>. This process may be referred to as a “failover.”

0028In selected embodiments, each server <b>206</b> may include one or more processors <b>212</b> and memory <b>214</b>. The memory <b>214</b> may include volatile memory (e.g., RAM) as well as non-volatile memory (e.g., ROM, EPROM, EEPROM, hard disks, flash memory, etc.). The volatile and non-volatile memory may, in certain embodiments, store software modules that run on the processor(s) <b>212</b> and are used to access data in the storage drives <b>204</b>. The servers <b>206</b> may host at least one instance of these software modules. These software modules may manage all read and write requests to logical volumes in the storage drives <b>204</b>.

0029One example of a storage system <b>110</b> having an architecture similar to that illustrated in <figref idref="DRAWINGS">FIG. 2</figref> is the IBM DS8000™ enterprise storage system. The DS8000™ is a high-performance, high-capacity storage controller providing disk storage that is designed to support continuous operations. Nevertheless, the apparatus and methods disclosed herein are not limited to operation with the IBM DS8000™ enterprise storage system <b>110</b>, but may operate with any comparable or analogous storage system <b>110</b>, regardless of the manufacturer, product name, or components or component names associated with the system <b>110</b>. Furthermore, any storage system that could benefit from one or more embodiments of the invention is deemed to fall within the scope of the invention. Thus, the IBM DS8000™ is presented only by way of example and is not intended to be limiting.

0030Referring to <figref idref="DRAWINGS">FIG. 3</figref>, as previously mentioned, as network environments and storage-area-networks grow in usage and popularity, an increasing number of subscribers (e.g., host systems <b>106</b>) and applications (e.g., applications running on host systems <b>106</b>) may be configured to share connectivity to storage devices <b>204</b> and logical volumes <b>304</b> that are virtualized from the storage devices <b>204</b>. A storage virtualization layer <b>306</b> may provide the mapping between the logical volumes <b>304</b> and the storage devices <b>204</b>. Shared storage typically simplifies management and enables a single logical resource to be used by multiple subscribers or applications. It also typically reduces the underutilization of storage resources. This is because different systems or application may require different amounts of storage, and sharing the storage enables the different systems or application to use the amount of storage they need without wasting or underutilizing storage. As needs change, more or less storage may be allocated to the shared storage environment, thereby simplifying the scaling of storage resources.

0031Despite its advantages, shared storage is not without drawbacks. For example, shared storage may lead to resource contention as multiple systems or applications attempt to access the shared storage. Shared storage may also give rise to various security issues. Because multiple systems or application may access the same storage, the potential arises for certain systems or applications to access data or storage space that is only intended for or authorized to be used by other systems or applications. Although different security products may be available to limit access to data, these security products typically don't protect data at the volume level. As a result, programs such as I/O channel programs may be used to directly access data sets outside of normal access methods and security procedures. For example, a program may be written with a STARTIO instruction to issue READ commands to access data that should be within protected datasets, or WRITE commands to corrupt the same data.

0032In order to address the issues identified above, systems and methods are disclosed herein to add an additional layer of security to shared storage and decrease the potential that shared data or volumes will be accessed in an unauthorized manner. This functionality may be embodied as one or more modules implemented in software, hardware, firmware, or combinations thereof. For example, in certain embodiments, an I/O authorization control module <b>300</b> may be implemented on a host system <b>106</b> to limit I/O access to certain logical volumes <b>304</b> and/or storage devices <b>204</b> on a shared storage system <b>110</b>. This I/O authorization control module <b>300</b> may, in certain embodiments, protect data at the volume (either physical or logical) level. Each host system <b>106</b> that accesses the shared storage system <b>110</b> may include an I/O authorization control module <b>300</b>.

0033In general, the I/O authorization control module <b>300</b> may provide an additional layer of security to a shared storage system <b>110</b> and decrease the potential for user error by limiting which applications or subscribers can gain access to particular logical volumes <b>304</b> or storage devices <b>204</b>, or subsets thereof. For example, the I/O authorization control module <b>300</b> may ensure that only database applications have access to database data on the shared storage system <b>110</b>, while other applications on the host system <b>106</b> are denied access.

0034As shown in <figref idref="DRAWINGS">FIG. 3</figref>, in certain embodiments, an I/O authorization control module <b>300</b> in accordance with the invention may utilize one or more filter lists <b>302</b> to limit I/O access to a shared storage system <b>110</b>. Each filter list <b>302</b> may be associated with a particular logical or physical volume, or a subset thereof, and may contain a list of address spaces that are authorized to access the volume. In certain embodiments, each of these address spaces may be associated with a particular job or application.

0035Assuming each filter list <b>302</b> is associated with a logical volume <b>304</b>, when an I/O request is received for a particular logical volume <b>304</b>, the I/O authorization control module <b>300</b> may check whether a filter list <b>302</b> exists for the logical volume <b>304</b>. If so, the I/O authorization control module <b>300</b> may check whether the I/O request originates from one of the address spaces identified in the filter list <b>302</b>. If so, the I/O authorization control module <b>300</b> may pass the I/O request to the logical volume <b>304</b>. If, on the other hand, the I/O request does not originate from one of the address spaces referenced in the filter list <b>302</b>, the I/O authorization control module <b>300</b> may block the I/O request and thereby prevent access to the logical volume <b>304</b>.

0036Referring to <figref idref="DRAWINGS">FIG. 4</figref>, a process flow diagram is presented showing a generalized method <b>400</b> for limiting I/O access in a shared storage system <b>110</b>. Such a method <b>400</b> may be executed by the I/O authorization control module <b>300</b> previously discussed in association with <figref idref="DRAWINGS">FIG. 3</figref>. As shown, the method <b>400</b> initially determines <b>402</b> whether an I/O request has been received. If so, the method <b>400</b> determines <b>404</b> whether the I/O request is a system-level I/O request (e.g., an I/O request that is associated with operating system or system recovery operations, such as initializing devices for use and/or recovering from certain types of errors,). If the I/O request is a system-level I/O request, the method <b>400</b> passes <b>416</b> the I/O request to the logical volume <b>304</b> it is intended for (thereby allowing the I/O request to be executed on the logical volume <b>304</b>) and the method <b>400</b> returns to the top to wait <b>402</b> for the next I/O request.

0037If, at step <b>404</b>, the I/O request is not a system-level I/O request, the method <b>400</b> determines <b>406</b> the address space associated with the I/O request. The method <b>400</b> further determines <b>408</b> the logical volume <b>304</b> associated with the I/O request and, at step <b>410</b>, determines whether a filter list <b>302</b> is associated with the logical volume <b>304</b>. If a filter list <b>302</b> is associated with the logical volume <b>304</b>, the method <b>400</b> determines <b>412</b> whether the I/O request is associated with an address space in the filter list <b>302</b> (i.e., the I/O request originates from a job or application identified by address space in the filter list <b>302</b>). If so, the method <b>400</b> passes <b>416</b> the I/O request to the logical volume <b>304</b> identified at step <b>408</b> and the method <b>400</b> waits <b>402</b> for the next I/O request. If not, the method <b>400</b> blocks <b>414</b> the I/O request and, in certain embodiments, returns <b>414</b> an error code or message indicating the I/O request was blocked. The method <b>400</b> then returns to the top to wait <b>402</b> for the next I/O request.

0038Referring to <figref idref="DRAWINGS">FIG. 5</figref>, a high-level block diagram is provided showing various control blocks and data structures for use in an exemplary z/OS implementation in accordance with the invention. These control blocks and data structures are exemplary in nature and are not intended to limit the scope of the invention.

0039In the z/OS operating system environment, I/O drivers may invoke I/O Supervisor (IOS) to submit an I/O request by issuing a STARTIO macro. Today, this includes passing control through a Start Subchannel Queuing Routine, which will in turn call a Start Subchannel Module. The STARTIO interface includes passing an I/O Supervisor Block <b>500</b> (IOSB), which includes an IOSASID field <b>510</b> that contains an Address Space Identifier (ASID) of the address space that requested the I/O. The IOSB <b>500</b> may also contain a 1-byte IOSCOD field <b>512</b> indicating the result of the I/O request.

0040In z/OS, an I/O device is represented by a Unit Control Block <b>502</b> (UCB). The UCB <b>502</b> may contain a 1-byte UCBLEVEL field <b>516</b>, and a 1-byte IOSLEVEL field <b>514</b>, which together dictate a hierarchy of allowable I/O requests. An I/O request will only be passed to a device/volume if the IOSLEVEL <b>514</b> in the IOSB <b>500</b> is greater than or equal to the UCBLEVEL <b>516</b> in the UCB <b>502</b>. A UCBLEVEL <b>516</b> and IOSLEVEL <b>514</b> of one is the lowest level, which may be referred to as a User Level or Normal Level, which is used for normal application I/O. Any level greater than one may be used for system-level operations. For example, the I/O SUPERVISOR may raise the UCBLEVEL <b>516</b> to a hexadecimal value of x‘0A’ and issue I/O requests with an IOSLEVEL <b>514</b> having a hexadecimal value of x‘0A’ when establishing path groups to a device. This temporarily prevents other I/O requests from being initiated during that time, which prevents normal application I/O from interfering with system-level I/O. Systems and methods in accordance with the invention may enable only a limited number of address spaces to request I/O from particular devices/volumes, while also enabling system-level I/O to proceed without filtering.

0041In certain embodiments, a user may input one or more device exclusivity lists into a SYS1.PARMLIB member <b>506</b>, each of which may contain a range <b>524</b> of devices/volumes and names <b>526</b> of jobs that are authorized to perform I/O to the devices/volumes. In such an implementation, the jobs associated with the job names <b>526</b> are the only jobs authorized to perform I/O to the range of devices/volumes. I/O requests from other jobs will be rejected. Using this information <b>506</b>, z/OS may build the control blocks shown in <figref idref="DRAWINGS">FIG. 5</figref> when the devices/volumes are first brought online to the system, either at initial program load (IPL) time or through the device vary online process.

0042Systems and methods in accordance with the invention may introduce a new UCBAFLST field <b>518</b> within the UCB <b>502</b>, and a new control block <b>504</b> referred to herein as an address space filter list <b>504</b>, which is pointed to by the UCBAFLST field <b>518</b>. The address space filter list <b>504</b> may contain an array with a count <b>520</b> of allowable address spaces followed by an ASID <b>522</b> for each of the allowable address spaces. Alternatively, the address space filter list <b>504</b> may be embodied as a hash table containing the allowable ASIDs and the UCBAFLST field <b>518</b> may point to this hash table. The ASID may be used as the hash table key, and the hash table may contain a representation for “ASID allowed” or “ASID not allowed.”

0043Referring to <figref idref="DRAWINGS">FIG. 6</figref>, while continuing to refer generally to <figref idref="DRAWINGS">FIG. 5</figref>, a process flow diagram is provided showing how the control blocks of <figref idref="DRAWINGS">FIG. 5</figref> are utilized when limiting I/O access in a shared storage system <b>110</b>. The method <b>600</b> is a narrower implementation of the method <b>400</b> of <figref idref="DRAWINGS">FIG. 4</figref> in a particular environment, namely the z/OS environment. Systems and methods in accordance with the invention may introduce new “startability” checks within the Start Subchannel Queueing Routine. When the Start Subchannel Queueing Routine obtains control for a STARTIO request at step <b>602</b>, the I/O SUPERVISOR checks <b>604</b> whether the content of the IOSLEVEL field <b>514</b> is greater than one, which indicates that the I/O request is associated with system-level I/O. If so, the method <b>600</b> bypasses most of the processing logic in the method <b>600</b> and proceeds to build <b>620</b> I/O Queue Element (IOQ) and related control blocks <b>528</b> (See <figref idref="DRAWINGS">FIG. 5</figref>) and pass <b>622</b> information to the IOSVSSCH process to start the I/O request.

0044If, at step <b>604</b>, the content of the IOSLEVEL field <b>514</b> is not greater than one, the I/O SUPERVISOR checks <b>606</b> whether the content of the UCBFLST field <b>518</b> is nonzero to determine if an address space filter list <b>504</b> exists for the device/volume that is the target of the I/O request. If the content of the UCBFLST field <b>518</b> is not nonzero, then no address space filter list <b>504</b> exists for the device/volume and the I/O request is processed in the conventional manner without invoking the filtering logic.

0045If, on the other hand, the content of the UCBFLST field <b>518</b> is nonzero, then the I/O SUPERVISOR retrieves the address space filter list <b>504</b> and traverses the list of allowable address spaces to determine if the ASID contained in the IOSASID field <b>510</b> is referenced in the list <b>504</b>. This includes obtaining <b>608</b> the first field <b>520</b> in the address space filter list <b>504</b> to get the count of ASIDs <b>522</b>, and checking <b>608</b> the next field, which is the first ASID within the array. If the ASID in the address space filter list <b>504</b> matches <b>610</b> the ASID in the IOSASID field <b>510</b> of the IOSB control block <b>500</b>, then the I/O request is passed to the device/volume that is the target of the I/O request. If not, the remaining ASIDs in the array are checked <b>618</b> until either a match is found or the end of the address space filter list <b>504</b> is reached (i.e., the ASID count <b>520</b> is exceeded <b>612</b>).

0046If the end of the address space filter list <b>504</b> is reached and no match is found, thereby indicating that the IOSASID <b>510</b> did not match any of the allowable ASIDs in the address space filter list <b>504</b>, then the I/O request is blocked <b>613</b> (i.e., not passed to the device/volume). When this occurs, the method <b>600</b> may insert <b>614</b> an error code into the IOSCOD field <b>512</b> of the IOSB <b>500</b> to indicate that the I/O request was not allowed to complete. In certain embodiments, the method <b>600</b> further schedules an IOS post status routine to post <b>616</b> the I/O requestor with the error status.

0047The flowcharts and block diagrams in the Figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in the flowcharts or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the Figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. Other implementations may not require all of the disclosed steps to achieve the desired functionality. It will also be noted that each block of the block diagrams and/or flowchart illustrations, and combinations of blocks in the block diagrams and/or flowchart illustrations, may be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.