Abstract:
An apparatus receives virtualization manager indication of a capability selected from a virtualization manager capability subset. The apparatus receives non-virtualization manager indication of a selected capability not in said subset. The apparatus passes virtualization manager indication of a result of the capability selected from the subset. The apparatus passes non-virtualization manager indication of a result of the capability not in said subset.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates to the field of virtualization and, in particular, to the provision of access to hypervisor capabilities. 
       BACKGROUND 
       [0002]    Within a virtualization environment, a hypervisor may possess various capabilities beyond providing emulation. For instance, a hypervisor may be able to start and stop virtual machines, provide storage to virtual machines, and/or provide networking to virtual machines. 
         [0003]    Moreover, a user (e.g., a system administrator) may be afforded access to hypervisor capabilities. However, such access is typically funneled through a virtualization manager, with the user&#39;s access to hypervisor capabilities being constrained to whatever subset of those capabilities is deigned to be offered via the virtualization manager. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    The present disclosure is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings. 
           [0005]      FIG. 1  illustrates an example network architecture in which examples of the present invention may operate. 
           [0006]      FIG. 2  sets forth operations involving provision of access to hypervisor capabilities, according to an example. 
           [0007]      FIG. 3  is a flow diagram illustrating a method of providing access to hypervisor capabilities, according to an example. 
           [0008]      FIGS. 4A ,  4 B, and  4 C illustrate graphical user interfaces (GUIs), according to an example. 
           [0009]      FIG. 5  is a diagrammatic representation of a machine, according to an example. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    Within a virtualization environment, a hypervisor may possess various capabilities beyond providing emulation. For instance, a hypervisor may be able to start and stop virtual machines, provide storage to virtual machines, and/or provide networking to virtual machines. With the passage of time, the hypervisor may gain additional capabilities (e.g., in connection with releases of new version of the hypervisor). 
         [0011]    Moreover, a user (e.g., a system administrator) may be afforded access to hypervisor capabilities. However, such access is typically funneled through a virtualization manager, with the user&#39;s access to hypervisor capabilities being constrained to whatever subset of those capabilities is deigned to be offered via the virtualization manager. Not only might certain existing hypervisor capabilities be excluded from those available to the user, but the gap between broader capabilities of the hypervisor and those available to the user may widen with time as, say, version releases of the hypervisor outstrip those of the virtualization manager. 
         [0012]    Set forth herein are examples of approaches by which a user may be able to more broadly access hypervisor capabilities. According to an example, a user may be allowed access to hypervisor capabilities in a fashion that bypasses the virtualization manager. A user interface may, bypassing the virtualization manger, directly access the hypervisor via a hypervisor accessor. In so doing the user interface may allow the user to access hypervisor capabilities which would have been inaccessible had he remained limited to virtualization manager-constrained access. Moreover, according to an example, the hypervisor accessor may query the hypervisor as to the hypervisor&#39;s full range of capabilities, and then the full range of capabilities may be made available to the user via the user interface. According to an additional example, capabilities may be offered to the user which go beyond the raw capabilities of the hypervisor. 
         [0013]    The following description sets forth numerous specific details such as examples of specific systems, components, methods, and so forth, in order to provide a good understanding of several embodiments of the present invention. It will be apparent to one skilled in the art, however, that at least some embodiments of the present invention may be practiced without these specific details. In other instances, well-known components or methods are not described in detail or are presented in simple block diagram format in order to avoid unnecessarily obscuring the present invention. Thus, the specific details set forth are merely examples. Particular implementations may vary from these example-only details and still be contemplated to be within the scope of the present invention. 
         [0014]      FIG. 1  illustrates an example network architecture  100  in which examples of the present invention may operate. The network architecture  100  includes one or more host servers  103  coupled to clients  101  over a network  102 . The network  102  may be a private network (e.g., a local area network (LAN), wide area network (WAN), intranet, etc.) or a public network (e.g., the Internet). The host servers  103  may also be coupled to a host controller  107  (via the same or a different network or directly). Host controller  107  may be an independent machine such as a server computer, a desktop computer, etc. Alternatively, the host controller  107  may be part of the host servers  103 . In one example, the network architecture  100 , including host controller  107 , host servers  103  and clients  101 , may be referred to as a virtualization environment. 
         [0015]    In one example, the clients  101  may include computing devices that have a wide range of processing capabilities. Some or all of the clients  101  may be thin clients, which serve as access terminals for users and depend primarily on the host servers  103  for processing activities. For example, the client  101  may be a desktop computer, laptop computer, cellular phone, personal digital assistant (PDA), etc. The client  101  may run client applications such as a Web browser. The client  101  may also run other client applications, which receive multimedia data streams or other data from the host server  103  and re-direct the received data to a local display or other user interface. 
         [0016]    Host servers  103  may include server computers or any other computing devices capable of running one or more virtual machines  131 . Each virtual machine  131  runs a guest operating system (OS) that may be different from one virtual machine to another. The guest OS may include Microsoft Windows, Linux, Solaris, Mac OS, etc. The host server  103  may include a hypervisor  132  that emulates the underlying hardware platform for the virtual machines  131 . The hypervisor  132  may also be known as a virtual machine monitor (VMM) or a kernel-based hypervisor. The host server  103  may include hypervisor accessor  153 . As discussed in greater detail hereinbelow, hypervisor accessor  153  may perform operations including allowing a user access to hypervisor capabilities in a fashion that bypasses the virtualization manager. 
         [0017]    Each virtual machine  131  can be accessed by one or more of the clients  101  over the network  102  and can provide a virtual desktop for the client(s)  101 . From the user&#39;s point of view, the virtual desktop functions as a physical desktop (e.g., a personal computer) and is indistinguishable from a physical desktop. Each virtual machine  131  may be linked to one or more virtual disks. These virtual disks can be logical partitions of a physical disk managed by hypervisor  132 , can be cloud based storage devices, or can be some other type of virtual storage device. In one example, virtual disks may form a whole or part of a logical data center. In one example, virtual machines  131  and virtual disks, together with host servers  103 , may be collectively referred to as entities in a virtual machine system. 
         [0018]    The virtual machines  131  and virtual disks are managed by the host controller  107 . Host controller  107  may manage the allocation of resources from host server  103  to virtual machines  131 . In addition, host controller may monitor the status of virtual machines  131  as well as the progress of commands and processes being executed by virtual machines  131  and/or on virtual machines  131 . The host controller  107  may include a virtualization manager  114  to perform management operations in the virtualization system, including for example allocating resources of host servers  103  to virtual machines  131 , monitoring the status of virtual machines  131 , monitoring the progress of commands and processes being executed by virtual machines  131 , etc. The host controller  107  may include user interface  151 . As discussed in greater detail hereinbelow, user interface  151  may perform operations including directly accessing the hypervisor via hypervisor accessor  153 , thus bypassing virtualization manager  114 . The host controller  107  may also maintain a management database  109  used by the virtualization manager  114  for the above management operations. 
         [0019]    In one example, host controller  107  also includes a package maintainer  112  to install, upgrade, or configure software packages on the host controller  107  in a consistent manner. For example, the package maintainer  112  may be used to install or upgrade the virtualization manager  114  on the host controller  107 . 
         [0020]      FIG. 2  sets forth one example of operations involving provision of access to hypervisor capabilities. The operations may be performed by processing logic that comprises hardware (e.g., circuitry, dedicated logic, programmable logic, microcode, etc.), software (such as instructions run on a processing device), or a combination thereof. As one example, the operations may be performed by a user interface running on a computing device, a hypervisor accessor running on a computing device, a virtualization manager running on a computer device, and a hypervisor running on a computing device For instance, the operations may be performed by user interface  151  running on host controller  107 , hypervisor accessor  153  running on host server  103 , virtualization manager  114  running on host controller  107 , and hypervisor  132  running on host server  103 . 
         [0021]    In a first aspect, illustrated by way of  FIG. 2  is user interface  151  providing access to capabilities of hypervisor  132  via virtualization manager  114 . As one example, such provision of access may involve user interface  151  (e.g., via a Graphical User Interface (GUI)) offering one or more of that subset of hypervisor  132 &#39;s capabilities which are being made available by virtualization manager  132 , receiving user selection of one or more of those capabilities, receiving one or more elements of user input to be employed in connection with the selected capabilities, and/or passing to virtualization manager  114  that which has been received from the user. Virtualization manager  114  may then provide to hypervisor  132  corresponding indication of the one or more selected capabilities, and/or appropriate information which will allow the selected one or more capabilities to be carried out. As one illustration, a selected capability might relate to providing a virtual machine of hypervisor  132  with access to a virtual Local Area Network (vLAN), and the elements of user input may regard indication of the vLAN to be applied and of the virtual machine to which the vLAN is to be applied. 
         [0022]    Hypervisor  132  may then perform one or more operations to carry out the requested one or more capabilities (e.g., to carry out provision of the vLAN). Having done so hypervisor  132  may pass one or more capability results to virtualization manager  114  (e.g., indication of successful provision of a vLAN to a virtual machine). Virtualization manager  114  may then provide corresponding information (e.g., regarding the successful vLAN provision) to user interface  151 , and user interface  151  may display corresponding indication to the user (e.g., indication that the vLAN has been successfully provisioned). 
         [0023]    Such interplay amongst user interface  151 , virtualization manager  114 , and hypervisor  132  may, for example, involve the employ of interprocess communication (e.g., XML-Remote Procedure Call (XML-RPC) Web Toolkit-Remote Procedure Call (GWT-RPC)). User interface  151  may, for example, learn via interprocess communication of the subset of hypervisor  132 &#39;s capabilities which are being made available by virtualization manager  132 . 
         [0024]    In a second aspect, illustrated by way of  FIG. 2  is user interface  151  providing access to capabilities of hypervisor  132  without involving virtualization manager  114 . Relative at least to the via-virtualization manager capabilities access discussed hereinabove, such access not involving virtualization manager  114  might be viewed access provision which bypasses virtualization manager  114 . 
         [0025]    As one example such provision of access may involve user interface  151  (e.g., via a GUI) offering one or more of hypervisor  132 &#39;s capabilities including ones beyond the subset of capabilities which has been made available by virtualization manager  114 , receiving user selection of one or more of those capabilities, receiving one or more elements of user input to be employed in connection with the selected capabilities, and/or passing to hypervisor accessor  153  that which has been received from the user. Hypervisor accessor  153  may then provide to hypervisor  132  corresponding indication of the one or more selected capabilities, and/or appropriate information which will allow the selected one or more capabilities to be carried out. As one illustration, a selected capability might relate to a user learning of the statuses (e.g., pending, executing, and/or completed) of one or more tasks (e.g., disk image deletions) being handled by hypervisor  132 , with the user perhaps indicating particular jobs for which status is desired or indicating a desire to learn of all jobs. 
         [0026]    Hypervisor  132  may then perform one or more operations to carry out the requested one or more capabilities (e.g., to carry out provision of the requested task statuses). Having done so hypervisor  132  may pass one or more results to hypervisor accessor  153  (e.g., indication of the requested task statuses). Hypervisor accessor  153  may then provide corresponding information (e.g., regarding the requested task statuses) to user interface  151 , and user interface  151  may display corresponding indication to the user (e.g., indication of the task statuses). 
         [0027]    This interplay amongst user interface  151 , hypervisor accessor  153 , and hypervisor  132  may, for example, involve the following. In one aspect, user interface  151  employing Hypertext Markup Language (HTML) and/or JavaScript in interfacing with its user and/or in accessing one or more Common Gateway Interface (CGI) scripts hosted by hypervisor accessor  153  (e.g., via web server capability). In a further aspect hypervisor accessor  153  employing those one or more CGI scripts in interface with hypervisor  132  via a command line tool of hypervisor  132 . The CGI scripts may be written in one or more of a wide variety of languages. For instance, the scripts may be written in Perl, Python, and/or Bash. 
         [0028]    With an eye towards host controller  107 , it is observed that such employ of HTML and/or JavaScript does not call for, say, modification of virtualization manager  114 . As such, for instance, virtualization manager code need not be changed. In like vein, with an eye towards host server  103 , it is noted that such employ of CGI scripts does not call for, say, modification of hypervisor  132 . As such, for example, hypervisor code need not be changed. At least in view of the avoidance of modifying virtualization manager code and the avoidance of modifying hypervisor code, the noted use of HTML, JavaScript, and CGI scripts may be viewed as being a plugin architecture. 
         [0029]    As noted, hypervisor accessor  153  may employ the one or more CGI scripts in interface with hypervisor  132  via a command line tool of hypervisor  132 . According to an example, via the CGI scripts hypervisor  153  may evoke the command line tool of hypervisor  132  in such a way so as to provide hypervisor  132  the information called for in order to perform execution of the at-hand capability (e.g., via one or more arguments passed to the command line tool), and/or to receive from the command line tool pass of a result of the execution of the capability (e.g., via a retrieval of the output of the command line tool, such as an output which might otherwise be routed to a terminal from which the command line tool was evoked and/or to a console or log). Moreover, via the CGI script access user interface  151  may receive the result and provide appropriate indication thereof to the user (e.g., via the employ of HTML and/or JavaScript). 
         [0030]      FIG. 3  illustrates a flow diagram of one example of a method of providing access to hypervisor capabilities. The method may be performed by processing logic that comprises hardware (e.g., circuitry, dedicated logic, programmable logic, microcode, etc.), software (such as instructions run on a processing device), or a combination thereof. As one example, the method may be performed by a hypervisor accessor and a hypervisor running on a computing device. For instance, the method may be performed by hypervisor accessor  153  and hypervisor  132  running on host server  103 . As one example, the operations discussed in connection with  FIG. 3  may be performed in accordance with that which is discussed hereinabove in connection with  FIG. 2 . 
         [0031]    Referring to  FIG. 3 , at block  301  the processing logic may, in accordance with that which is discussed in connection with  FIG. 2 , receive from virtualization manager  114  indication of one or more selected capabilities and/or information which will allow the selected one or more capabilities to be carried out. 
         [0032]    At block  303  the processing logic may, in accordance with that which is discussed in connection with  FIG. 2 , receive from via user interface  151 , in a fashion not involving virtualization manager  114 , indication of one or more selected capabilities, and/or information which will allow the selected one or more capabilities to be carried out. 
         [0033]    At block  305  the processing logic may, in accordance with that which is discussed in connection with  FIG. 2 , perform one or more operations to carry out the one or more capabilities corresponding to the virtualization manager-provided indication. 
         [0034]    At block  307  the processing logic may, in accordance with that which is discussed in connection with  FIG. 2 , perform one or more operations to carry out the one or more capabilities corresponding to the user interface-provided indication. 
         [0035]    At block  309  the processing logic may, in accordance with that which is discussed in connection with  FIG. 2 , pass to virtualization manager  114  one or more results of the performance of the capabilities corresponding to the virtualization manager-provided indication. 
         [0036]    At block  311 , the processing logic may, in accordance with that which is discussed in connection with  FIG. 2 , make available to user interface  151 —in a fashion not involving virtualization manager  114 —one or more results of the performance of the capabilities corresponding to the indication received via user interface  151 . 
         [0037]    According to one example one or more particular hypervisor capabilities may be provided in a fashion that bypasses the virtualization manager. For instance, capabilities so provided may include, the ability to learn of the statuses (e.g., pending, executing, and/or completed) of one or more tasks (e.g., disk image deletions) being handled by the hypervisor (e.g., with the user perhaps indicating particular jobs for which status is desired or indicating a desire to learn of all jobs), the ability to learn of storage (e.g., storage clusters accessible to virtual machines of the hypervisor, the ability to learn of storage credential groupings (e.g., storage domains) accessible to virtual machines of the hypervisor, the ability to learn of virtual machines accessible via the hypervisor (e.g., with presentation in list and/or table form), the ability to get statistics (e.g., performance statistics) regarding the virtual machines of the hypervisor, the ability to get statistics (e.g., performance statistics) regarding the hypervisor itself, the ability to stop one or more virtual machines of the hypervisor, the ability to resume one or more virtual machines of the hypervisor, the ability to create one or more virtual machines to be hosted by the hypervisor, and/or the ability to establish user access (e.g., in a fashion employing Virtual Network Computing (VNC) or another approach allowing for GUI access) to one or more virtual machines of the hypervisor. 
         [0038]    According to another example, all hypervisor capabilities may be provided in a fashion that bypasses the virtualization manager. For instance, one or more CGI scripts hosted by hypervisor accessor  153  may act to query the hypervisor as to the entirety of its capabilities (i.e., of the full set of all of its capabilities), provide via user interface  151  (e.g., via the employ of HTML and/or JavaScript) a user with the ability to select any of the entirety of hypervisor capabilities and to provide called-for user input, interface with the hypervisor to pass to the hypervisor indication of the selected ability and the called-for information to execute the selected capability, retrieve the result of the performance of the capability, and provide via user interface  151  (e.g., via the employ of HTML and/or JavaScript) an appropriate indication of that result. 
         [0039]    According to another example, capabilities of host sever  103  beyond those of hypervisor  132  may be accessed via one or more CGI scripts hosted by the hypervisor accessor  153 . Such access might be implemented in a fashion akin to that discussed herein in connection with accessing hypervisor  153  (e.g., the CGI scripts may access such additional host server capabilities via interface with one or more command lines tools or executables). 
         [0040]    As an example, the employ of CGI scripts discussed herein—be it in connection with access to hypervisor  132 , or host server  103  capabilities beyond those of hypervisor  132 —may involve the setting of one or more permissions (e.g., by a system administrator and/or other user, and/or by the CGI scripts themselves and/or one or more automated processes). As another example there might not be such permissions setting (e.g., the CGI scripts may be able to perform called-for accesses even in absence of such permissions settings). 
         [0041]    According to an additional example, capabilities may be offered to the user which go beyond the raw capabilities of the hypervisor. For instance, one or more of those raw capabilities may be employed as base upon which new capabilities are built. For example, CGI functionality in the vein of that discussed hereinabove may employ one more hypervisor capabilities within a code structure (e.g., a loop) to effect new capabilities. As illustrations, a capability to learn of a given, identified job status may be employed within a loop to learn of all job statuses, a capability to pause a given, identified job may be employed within a loop to pause all job statuses, and/or a capability to delete a given, identified job may be employed within a loop to delete all job statuses. 
         [0042]    As discussed, hypervisor accessor employ may allow for access to hypervisor capabilities in a fashion that bypasses the virtualization manager. Such employ may allow a single user interface  153  to access multiple hypervisors. As one example, each such hypervisor may have its own hypervisor accessor (e.g., hosted by a corresponding host server of that hypervisor). As another example, a hypervisor accessor may allow access to multiple hypervisors. Such a hypervisor accessor might exist on a computing device (e.g., a server) apart from one or more host servers which include those hypervisors. Where the hypervisor accessor is on a different computing device than the hypervisor, interprocess communication may be employed (e.g., in hypervisor command line tool access). 
         [0043]      FIGS. 4A-4C  illustrate example GUIs in accordance with that which has been set forth hereinabove. Shown in  FIG. 4A  is pulldown GUI element  431  which has been displayed subsequent to activation (e.g., right-clicking) of selectable GUI element  433 . Selectable GUI element  433  sets forth “MyHost,” a name of a host server  103 . Pulldown GUI element  431  offers for selection four host server capabilities of the sort discussed herein. In particular, offered for selection by pulldown GUI element  431  are the host server capabilities “Storage Credential Groupings,” “Accessible Storage,” “Task Status,” and “All Capabilities.” “Storage Credential Groupings” refers to the discussed capability of allowing a user to learn of storage credential groupings. “Accessible Storage” refers to the discussed capability of allowing a user to learn of storage accessible to virtual machines of the hypervisor. “Task Status” refers to the discussed capability of allowing a user to learn of the statuses of one or more tasks being handled by the hypervisor. “All Capabilities” refers to the discussed capability of all hypervisor capabilities being provided in a fashion that bypasses the virtualization manager. 
         [0044]    Shown in  FIG. 4B  is an example popup window GUI element  451  corresponding to an example scenario in which “Task Status” has been selected via Pulldown GUI element  431  of  FIG. 4A . Shown is a corresponding “Task Status” output. Shown in  FIG. 4C  is an example popup window GUI element  461  corresponding to an example scenario in which, firstly, “All Capabilities” has been selected via Pulldown GUI element  431  of  FIG. 4A . Subsequently according to the example, pulldown GUI element  463  has allowed from selection amongst all of the capabilities of the hypervisor and the capability “list” has been selected. Then according to the example scenario, popup window element  461  produced information  465  regarding the selected “list” capability, with popup window element  461  further providing field GUI element  467 . Entered into this field element has been the “table” view option set forth by information  465 , and activated has been button GUI element  468 . Then, responsive to the button activation, shown has been “list” output  469 . 
         [0045]      FIG. 5  illustrates a diagrammatic representation of a machine in the example form of a computing device  500  within which a set of instructions, for causing the machine to perform any one or more of the methodologies discussed herein, may be executed. In alternative examples, the machine may be connected (e.g., networked) to other machines in a Local Area Network (LAN), an intranet, an extranet, or the Internet. The machine may operate in the capacity of a server or a client machine in a client-server network environment, or as a peer machine in a peer-to-peer (or distributed) network environment. The machine may be a personal computer (PC), a tablet computer, a set-top box (STB), a Personal Digital Assistant (PDA), a cellular telephone, a web appliance, a server, a network router, switch or bridge, or any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. Further, while only a single machine is illustrated, the term “machine” shall also be taken to include any collection of machines (e.g., computers) that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein. 
         [0046]    The example computing device  500  includes a processing device  502 , a main memory  504  (e.g., read-only memory (ROM), flash memory, dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM (RDRAM), etc.), a static memory  506  (e.g., flash memory, static random access memory (SRAM), etc.), and a secondary memory (e.g., a data storage device  518 ), which communicate with each other via a bus  508 . 
         [0047]    Processing device  502  represents one or more general-purpose processors such as a microprocessor, central processing unit, or the like. More particularly, the processing device  502  may be a complex instruction set computing (CISC) microprocessor, reduced instruction set computing (RISC) microprocessor, very long instruction word (VLIW) microprocessor, processor implementing other instruction sets, or processors implementing a combination of instruction sets. Processing device  502  may also be one or more special-purpose processing devices such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), network processor, or the like. Processing device  502  is configured to execute the processing logic (instructions  526 ) for performing the operations and steps discussed herein. 
         [0048]    The computing device  500  may further include a network interface device  522 . The computing device  500  also may include a video display unit  510  (e.g., a liquid crystal display (LCD) or a cathode ray tube (CRT)), an alphanumeric input device  512  (e.g., a keyboard), a cursor control device  514  (e.g., a mouse), and a signal generation device  520  (e.g., a speaker). 
         [0049]    The data storage device  518  may include a machine-readable storage medium (or more specifically a computer-readable storage medium)  524  on which is stored one or more sets of instructions  526  embodying any one or more of the methodologies or functions described herein. The instructions  526  may also reside, completely or at least partially, within the main memory  504 , within the static memory  506  and/or within the processing device  502  during execution thereof by the computer system  500 , the main memory  504 , static memory  506  and the processing device  502  also constituting computer-readable storage media. 
         [0050]    While the computer-readable storage medium  524  is shown in an example to be a single medium, the term “computer-readable storage medium” should be taken to include a single medium or multiple media (e.g., a centralized or distributed database, and/or associated caches and servers) that store the one or more sets of instructions. The term “computer-readable storage medium” shall also be taken to include any medium other than a carrier wave that is capable of storing or encoding a set of instructions for execution by the machine and that cause the machine to perform any one or more of the methodologies of the present invention. The term “computer-readable storage medium” shall accordingly be taken to include, but not be limited to, solid-state memories, and optical and magnetic media. 
         [0051]    Although the operations of the methods herein are shown and described in a particular order, the order of the operations of each method may be altered so that certain operations may be performed in an inverse order or so that certain operation may be performed, at least in part, concurrently with other operations. In another embodiment, instructions or sub-operations of distinct operations may be in an intermittent and/or alternating manner. It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent upon reading and understanding the above description. Although embodiments of the present invention have been described with reference to specific example embodiments, it will be recognized that the invention is not limited to the embodiments described, but can be practiced with modification and alteration within the spirit and scope of the appended claims. Accordingly, the specification and drawings are to be regarded in an illustrative sense rather than a restrictive sense. The scope of the invention should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. Furthermore, the terms “first,” “second,” “third,” “fourth,” etc. as used herein are meant as labels to distinguish among different elements and may not necessarily have an ordinal meaning according to their numerical designation.