Patent Publication Number: US-2021182239-A1

Title: Trusted File Indirection

Description:
CROSS REFERENCE TO RELATED CASES 
     This application is a continuation of U.S. application Ser. No. 15/992,235, filed May 30, 2018, which is a continuation of U.S. application Ser. No. 14/335,466, filed Jul. 18, 2014, now U.S. Pat. No. 10,013,421, issued Jul. 3, 2018, which is a continuation of U.S. application Ser. No. 13/453,188, filed Apr. 23, 2012, now U.S. Pat. No. 8,819,090, issued Aug. 26, 2014, the disclosures of which are hereby incorporated by reference in their entirety for all purposes. 
    
    
     FIELD 
     This application generally relates to computers and computer networks. In particular, this application relates to methods and systems for transferring files between virtual machines when at least one of the machines is untrusted. 
     BACKGROUND 
     Traditionally, personal computers included operating systems, applications, and user settings for a single user. Personal computers were generally both used and managed by their owners. However, many organizations are now using virtualization, remote access and/or clouds of computing resources to fulfill their computing needs. Clouds of virtualized computing resources generally allow for the operating systems, applications, and user settings of multiple users to be included on a single physical machine. Desktop virtualization technology allows multiple instances of an operating system to be kept separate, so the activities of one user does not affect the experience of other users. Cloud computing environments allow for computers owned by the cloud operator to be managed by the cloud operator but used by cloud users, who may be customers of the cloud operator. Cloud users, however, may include any person who signs up or enrolls in such a service, and therefore little may be known about the integrity of any given cloud subscriber or user. Thus, access to files on a trusted domain is not given to users of guest domains. 
     SUMMARY 
     In light of the foregoing background, the following presents a simplified summary of the present disclosure in order to provide a basic understanding of some aspects described herein. This summary is not an extensive overview, and it is not intended to identify key or critical elements or to delineate the scope of the claims. The following summary merely presents various described aspects in a simplified form as a prelude to the more detailed description provided below. 
     According to an aspect of the disclosure, a method of transferring data may be performed by receiving an indication that a data update is available to a guest domain executing on a hypervisor, where the data update includes one or more data files in a file system of a trusted domain executing on the hypervisor, and then aliasing each of the one or more data files to be accessible through a file system of the guest domain. Shared data may include one or more files, directories, and/or other locations of data. 
     According to one aspect, aliasing may be performed by a proxy driver intercepting file system calls within the guest domain and determining whether to execute each file system call within the file system of the guest domain or to pass the file system call to the trusted domain. 
     Aspects described herein may be performed by a virtualization server, or by software stored on computer readable media and executed by one or more processors. For example, one or more computer readable storage media may store computer executable instructions that, when executed, perform data transfer between a trusted domain and a guest domain executing on a hypervisor. The guest domain may receive an indication that shared data is available. A proxy driver executing in the guest domain may intercept a file system call associated with the shared data. The driver may send the file system call associated with the shared data to the trusted domain. The trusted domain may execute the file system call associated with the shared data, and return information to the guest domain based on execution of the file system call associated with the shared data. 
     In some aspects, the proxy driver may pass each file system call to the trusted domain using one or more pages of shared memory allocated to the guest domain. The trusted domain may execute the file system call on an associated data file in the file system of the trusted domain, and pass a response (e.g., requested data, an acknowledgement, etc.) back to the guest domain via the shared memory. 
     According to some aspects, the trusted domain may store a key value store (or database) that stores file metadata regarding shared files. A key value monitor executing in a guest domain may monitor the key value store for changes, and update a file system database administered by a proxy driver in the guest domain based on the shared file metadata (e.g., file name, file type, file location, file size, file date(s), etc.). 
     In one embodiment, a processor of a virtualization server may execute instructions stored in a memory to perform trusted file indirection. The virtualization server may include a hypervisor for managing execution of a multiple virtual machine (VM) instances, where each VM is allocated a different portion of memory. There may be a first VM instance executing on the hypervisor, where the first VM instance is a trusted server domain for administration of the server. The first VM instance may be allocated a first region of memory. There may be a second VM instance executing on the hypervisor, where the second VM instance is an untrusted domain associated with a customer user of the server device. The second VM instance may be allocated a second region of memory. The server may further store or access shared data stored in the first region of memory allocated to the first VM instance and designated as accessible by the second VM instance. There may further be a proxy driver executing within the second VM instance, where the proxy driver is configured to intercept file system calls within the second VM instance and, when an intercepted file system call is associated with the shared data, proxy the file system call to the first VM instance for execution. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Having thus described aspects of the disclosure in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
         FIG. 1  illustrates an example operating environment in which various aspects of the disclosure may be implemented. 
         FIG. 2  illustrates a computing device that may be used in accordance with one or more illustrative aspects described herein. 
         FIG. 3  illustrates a computing device that may be used in accordance with one or more illustrative aspects described herein. 
         FIG. 4  is a block diagram that depicts embodiments of a virtualization server in accordance with one or more illustrative aspects described herein. 
         FIG. 5  illustrates an example system architecture in which aspects described herein may be performed. 
         FIG. 6  illustrates a method of updating shared file information according to one or more aspects describe herein. 
         FIG. 7  illustrates a method of performing trusted file indirection according to one or more aspects described herein. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description of the various embodiments, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration various embodiments in which aspects described herein may be practiced. It is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope and spirit of the present disclosure. 
     As will be appreciated by one of skill in the art upon reading the following disclosure, various aspects described herein may be embodied as a method, a data processing system, or a computer program product. Accordingly, those aspects may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, such aspects may take the form of a computer program product stored by one or more computer-readable storage media having computer-readable program code, or instructions, embodied in or on the storage media. Any suitable computer readable storage media may be utilized, including hard disks, CD-ROMs, optical storage devices, magnetic storage devices, and/or any combination thereof. In addition, various signals representing data or events as described herein may be transferred between a source and a destination in the form of electromagnetic waves traveling through signal-conducting media such as metal wires, optical fibers, and/or wireless transmission media (e.g., air and/or space). 
       FIG. 1  illustrates an example block diagram of a generic computing device  101  (e.g., a computer server  106   a ) in an example computing environment  100  that may be used according to one or more illustrative embodiments of the disclosure. According to one or more aspects, generic computing device  101  may be a server  106   a  in a single-server or multi-server desktop virtualization system (e.g., a cloud system) configured to provide virtual machines for client access devices. The generic computing device  101  may have a processor  103  for controlling overall operation of the server and its associated components, including random access memory (RAM)  105 , read-only memory (ROM)  107 , input/output (I/O) module  109 , and memory  115 . 
     I/O module  109  may include a mouse, keypad, touch screen, scanner, optical reader, and/or stylus (or other input device(s)) through which a user of generic computing device  101  may provide input, and may also include one or more of a speaker for providing audio output and a video display device for providing textual, audiovisual, and/or graphical output. Software may be stored within memory  115  and/or other storage to provide instructions to processor  103  for enabling generic computing device  101  to perform various functions. For example, memory  115  may store software used by the generic computing device  101 , such as an operating system  117 , application programs  119 , and an associated database  121 . Alternatively, some or all of the computer executable instructions for generic computing device  101  may be embodied in hardware or firmware (not shown). 
     The generic computing device  101  may operate in a networked environment supporting connections to one or more remote computers, such as terminals  140  (also referred to as client devices). The terminals  140  may be personal computers or servers that include many or all of the elements described above with respect to the generic computing device  101 . The network connections depicted in  FIG. 1  include a local area network (LAN)  125  and a wide area network (WAN)  129 , but may also include other networks. When used in a LAN networking environment, the generic computing device  101  may be connected to the LAN  125  through a network interface or adapter  123 . When used in a WAN networking environment, the generic computing device  101  may include a modem  127  or other network interface for establishing communications over the WAN  129 , such as computer network  130  (e.g., the Internet). It will be appreciated that the network connections shown are illustrative and other means of establishing a communications link between the computers may be used. 
     Generic computing device  101  and/or terminals  140  may also be mobile terminals (e.g., mobile phones, smartphones, PDAs, notebooks, etc.) including various other components, such as a battery, speaker, and antennas (not shown). 
     The disclosure is operational with numerous other general purpose or special purpose computing system environments or configurations. Examples of well-known computing systems, environments, and/or configurations that may be suitable for use with the disclosure include, but are not limited to, personal computers, server computers, hand-held or laptop devices, multiprocessor systems, microprocessor-based systems, set top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, distributed computing environments that include any of the above systems or devices, and the like. 
     As shown in  FIG. 1 , one or more client devices  140  may be in communication with one or more servers  106   a - 106   n  (generally referred to herein as “server(s)  106 ”). In one embodiment, the computing environment  100  can include an appliance installed between the server(s)  106  and client machine(s)  140 . This appliance can manage client/server connections, and in some cases can load balance client connections amongst a plurality of backend servers  106 . 
     The client machine(s)  140  can in some embodiment be referred to as a single client machine  140  or a single group of client machines  140 , while server(s)  106  may be referred to as a single server  106  or a single group of servers  106 . In one embodiment a single client machine  140  communicates with more than one server  106 , while in another embodiment a single server  106  communicates with more than one client machine  140 . In yet another embodiment, a single client machine  140  communicates with a single server  106 . 
     A client machine  140  can, in some embodiments, be referenced by any one of the following terms: client machine(s)  140 ; client(s); client computer(s); client device(s); client computing device(s); local machine; remote machine; client node(s); endpoint(s); endpoint node(s); or a second machine. The server  106 , in some embodiments, may be referenced by any one of the following terms: server(s), local machine; remote machine; server farm(s), host computing device(s), or a first machine(s). 
     In one embodiment, the client machine  140  may be a virtual machine. The virtual machine may be any virtual machine, while in some embodiments the virtual machine may be any virtual machine managed by a hypervisor developed by Citrix Systems, IBM, VMware, or any other hypervisor. In some aspects, the virtual machine may be managed by a hypervisor, while in aspects the virtual machine may be managed by a hypervisor executing on a server  106  or a hypervisor executing on a client  140 . 
     The client machine  140  may execute, operate or otherwise provide an application that can be any one of the following: software; a program; executable instructions; a virtual machine; a hypervisor; a web browser; a web-based client; a client-server application; a thin-client computing client; an ActiveX control; a Java applet; software related to voice over internet protocol (VoIP) communications like a soft IP telephone; an application for streaming video and/or audio; an application for facilitating real-time-data communications; a HTTP client; a FTP client; an Oscar client; a Telnet client; or any other set of executable instructions. Still other embodiments include a client device  140  that displays application output generated by an application remotely executing on a server  106  or other remotely located machine. In these embodiments, the client device  140  can display the application output in an application window, a browser, or other output window. In one example, the application is a desktop, while in other examples the application is an application that generates a desktop. A desktop may include a graphical shell providing a user interface for an instance of an operating system in which local and/or remote applications can be integrated. Applications, as used herein, are programs that execute after an instance of an operating system (and, optionally, also the desktop) has been loaded. 
     The server  106 , in some embodiments, executes a remote presentation client or other client or program that uses a thin-client or remote-display protocol to capture display output generated by an application executing on a server  106  and transmits the application display output to a remote client  140 . The thin-client or remote-display protocol can be any one of the following protocols: the Independent Computing Architecture (ICA) protocol manufactured by Citrix Systems, Inc. of Ft. Lauderdale, Fla.; or the Remote Desktop Protocol (RDP) manufactured by the Microsoft Corporation of Redmond, Wash. 
     The computing environment can include more than one server  106 A- 106 N such that the servers  106 A- 106 N are logically grouped together into a server farm  106 , for example, in a cloud computing environment. The server farm  106  can include servers  106  that are geographically dispersed and logically grouped together in a server farm  106 , or servers  106  that are located proximate to each other and logically grouped together in a server farm  106 . Geographically dispersed servers  106 A- 106 N within a server farm  106  can, in some embodiments, communicate using a WAN, MAN, or LAN, where different geographic regions can be characterized as: different continents; different regions of a continent; different countries; different states; different cities; different campuses; different rooms; or any combination of the preceding geographical locations. In some embodiments the server farm  106  may be administered as a single entity, while in other embodiments the server farm  106  can include multiple server farms  106 . 
     In some embodiments, a server farm  106  can include servers  106  that execute a substantially similar type of operating system platform (e.g., WINDOWS NT, manufactured by Microsoft Corp. of Redmond, Wash., UNIX, LINUX, or SNOW LEOPARD.) In other embodiments, the server farm  106  can include a first group of servers  106  that execute a first type of operating system platform, and a second group of servers  106  that execute a second type of operating system platform. The server farm  106 , in other embodiments, can include servers  106  that execute different types of operating system platforms. 
     The server  106 , in some embodiments, can be any server type. In other embodiments, the server  106  can be any of the following server types: a file server; an application server; a web server; a proxy server; an appliance; a network appliance; a gateway; an application gateway; a gateway server; a virtualization server; a deployment server; a SSL VPN server; a firewall; a web server; an application server or as a master application server; a server  106  executing an active directory; or a server  106  executing an application acceleration program that provides firewall functionality, application functionality, or load balancing functionality. In some embodiments, a server  106  may be a RADIUS server that includes a remote authentication dial-in user service. In embodiments where the server  106  comprises an appliance, the server  106  can be an appliance manufactured by any one of the following manufacturers: the Citrix Application Networking Group; Silver Peak Systems, Inc.; Riverbed Technology, Inc.; F5 Networks, Inc.; or Juniper Networks, Inc. Some embodiments include a first server  106 A that receives requests from a client machine  140 , forwards the request to a second server  106   n , and responds to the request generated by the client machine  140  with a response from the second server  106   n . The first server  106 A can acquire an enumeration of applications available to the client machine  140  and well as address information associated with an application server  106  hosting an application identified within the enumeration of applications. The first server  106 A can then present a response to the client&#39;s request using a web interface, and communicate directly with the client  140  to provide the client  140  with access to an identified application. 
     The server  106  can, in some embodiments, execute any one of the following applications: a thin-client application using a thin-client protocol to transmit application display data to a client; a remote display presentation application; any portion of the CITRIX ACCESS SUITE by Citrix Systems, Inc. like the METAFRAME or CITRIX PRESENTATION SERVER; MICROSOFT WINDOWS Terminal Services manufactured by the Microsoft Corporation; or an ICA client, developed by Citrix Systems, Inc. Another embodiment includes a server  106  that is an application server such as: an email server that provides email services such as MICROSOFT EXCHANGE manufactured by the Microsoft Corporation; a web or Internet server; a desktop sharing server; a collaboration server; or any other type of application server. Still other embodiments include a server  106  that executes any one of the following types of hosted servers applications: GOTOMEETING provided by Citrix Online Division, Inc.; WEBEX provided by WebEx, Inc. of Santa Clara, Calif.; or Microsoft Office LIVE MEETING provided by Microsoft Corporation. 
     Client machines  140  can, in some embodiments, be a client node that seeks access to resources provided by a server  106 . In other embodiments, the server  106  may provide clients  140  or client nodes with access to hosted resources. The server  106 , in some embodiments, functions as a master node such that it communicates with one or more clients  140  or servers  106 . In some embodiments, the master node can identify and provide address information associated with a server  106  hosting a requested application, to one or more clients  140  or servers  106 . In still other embodiments, the master node can be a server farm  106 , a client  140 , a cluster of client nodes  140 , or an appliance. 
     One or more clients  140  and/or one or more servers  106  can transmit data over a network  130  installed between machines and appliances within the computing environment  100 . The network  130  can comprise one or more sub-networks, and can be installed between any combination of the clients  140 , servers  106 , computing machines and appliances included within the computing environment  100 . In some embodiments, the network  130  can be: a local-area network (LAN); a metropolitan area network (MAN); a wide area network (WAN); a primary network  104  comprised of multiple sub-networks located between the client machines  140  and the servers  106 ; a primary public network  130  (e.g., the Internet) with a private sub-network; a primary private network  130  with a public sub-network; or a primary private network  130  with a private sub-network. Still further embodiments include a network  130  that can be any of the following network types: a point to point network; a broadcast network; a telecommunications network; a data communication network; a computer network; an ATM (Asynchronous Transfer Mode) network; a SONET (Synchronous Optical Network) network; a SDH (Synchronous Digital Hierarchy) network; a wireless network; a wireline network; or a network that includes a wireless link where the wireless link can be an infrared channel or satellite band. The network topology of the network  130  can differ within different embodiments, possible network topologies include: a bus network topology; a star network topology; a ring network topology; a repeater-based network topology; or a tiered-star network topology. Additional embodiments may include a network of mobile telephone networks that use a protocol to communicate among mobile devices, where the protocol can be any one of the following: AMPS; TDMA; CDMA; GSM; GPRS UMTS; or any other protocol able to transmit data among mobile devices. 
     Illustrated in  FIG. 2  is an embodiment of a computing device  200 , where the client machine  140  and server  106  illustrated in  FIG. 1  may be deployed as and/or executed on any embodiment of the computing device  200  illustrated and described herein. Included within the computing device  200  is a system bus  250  that communicates with the following components: a central processing unit  221 ; a main memory  222 ; storage memory  228 ; an input/output (I/O) controller  223 ; display devices  224 A- 224 N; an installation device  216 ; and a network interface  218 . In one embodiment, the storage memory  228  includes: an operating system, software routines, and a client agent  220 . The I/O controller  223 , in some embodiments, is further connected to a keyboard  226 , and a pointing device  227 . Other embodiments may include an I/O controller  223  connected to more than one input/output device  230 A- 230 N. 
       FIG. 3  illustrates one embodiment of a computing device  300 , where the client machine  140  and server  106  illustrated in  FIG. 1  can be deployed as and/or executed on any embodiment of the computing device  300  illustrated and described herein. Included within the computing device  300  is a system bus  350  that communicates with the following components: a bridge  370 , and a first I/O device  330   a . In another embodiment, the bridge  370  is in further communication with the main central processing unit  321 , where the central processing unit  321  can further communicate with a second I/O device  330   b , a main memory  322 , and a cache memory  340 . Included within the central processing unit  321 , are I/O ports, a memory port  303 , and a main processor. 
     Embodiments of the computing machine  300  can include a central processing unit  321  characterized by any one of the following component configurations: logic circuits that respond to and process instructions fetched from the main memory unit  322 ; a microprocessor unit, such as: those manufactured by Intel Corporation; those manufactured by Motorola Corporation; those manufactured by Transmeta Corporation of Santa Clara, Calif.; the RS/6000 processor such as those manufactured by International Business Machines; a processor such as those manufactured by Advanced Micro Devices; or any other combination of logic circuits. Still other embodiments of the central processing unit  322  may include any combination of the following: a microprocessor, a microcontroller, a central processing unit with a single processing core, a central processing unit with two processing cores, or a central processing unit with more than one processing core. 
     While  FIG. 3  illustrates a computing device  300  that includes a single central processing unit  321 , in some embodiments the computing device  300  can include one or more processing units  321 . In these embodiments, the computing device  300  may store and execute firmware or other executable instructions that, when executed, direct the one or more processing units  321  to simultaneously execute instructions or to simultaneously execute instructions on a single piece of data. In other embodiments, the computing device  300  may store and execute firmware or other executable instructions that, when executed, direct the one or more processing units to each execute a section of a group of instructions. For example, each processing unit  321  may be instructed to execute a portion of a program or a particular module within a program. 
     In some embodiments, the processing unit  321  can include one or more processing cores. For example, the processing unit  321  may have two cores, four cores, eight cores, etc. In one embodiment, the processing unit  321  may comprise one or more parallel processing cores. The processing cores of the processing unit  321 , may in some embodiments access available memory as a global address space, or in other embodiments, memory within the computing device  300  can be segmented and assigned to a particular core within the processing unit  321 . In one embodiment, the one or more processing cores or processors in the computing device  300  can each access local memory. In still another embodiment, memory within the computing device  300  can be shared amongst one or more processors or processing cores, while other memory can be accessed by particular processors or subsets of processors. In embodiments where the computing device  300  includes more than one processing unit, the multiple processing units can be included in a single integrated circuit (IC). These multiple processors, in some embodiments, can be linked together by an internal high speed bus, which may be referred to as an element interconnect bus. 
     In embodiments where the computing device  300  includes one or more processing units  321 , or a processing unit  321  including one or more processing cores, the processors can execute a single instruction simultaneously on multiple pieces of data (SIMD), or in other embodiments can execute multiple instructions simultaneously on multiple pieces of data (MIMD). In some embodiments, the computing device  100  can include any number of SIMD and MIMD processors. 
     The computing device  300 , in some embodiments, can include a graphics processor or a graphics processing unit (Not Shown). The graphics processing unit can include any combination of software and hardware, and can further input graphics data and graphics instructions, render a graphic from the inputted data and instructions, and output the rendered graphic. In some embodiments, the graphics processing unit can be included within the processing unit  321 . In other embodiments, the computing device  300  can include one or more processing units  321 , where at least one processing unit  321  is dedicated to processing and rendering graphics. 
     One embodiment of the computing machine  300  includes a central processing unit  321  that communicates with cache memory  340  via a secondary bus also known as a backside bus, while another embodiment of the computing machine  300  includes a central processing unit  321  that communicates with cache memory via the system bus  350 . The local system bus  350  can, in some embodiments, also be used by the central processing unit to communicate with more than one type of I/O device  330   a - 330   n . In some embodiments, the local system bus  350  can be any one of the following types of buses: a VESA VL bus; an ISA bus; an EISA bus; a MicroChannel Architecture (MCA) bus; a PCI bus; a PCI-X bus; a PCI-Express bus; or a NuBus. Other embodiments of the computing machine  300  include an I/O device  330   a - 330   n  that includes a video display  224  that communicates with the central processing unit  321 . Still other versions of the computing machine  300  include a processor  321  connected to an I/O device  330   a - 330   n  via any one of the following connections: HyperTransport, Rapid I/O, or InfiniBand. Further embodiments of the computing machine  300  include a processor  321  that communicates with one I/O device  330   a  using a local interconnect bus and a second I/O device  330   b  using a direct connection. 
     The computing device  300 , in some embodiments, includes a main memory unit  322  and cache memory  340 . The cache memory  340  can be any memory type, and in some embodiments can be any one of the following types of memory: SRAM; BSRAM; or EDRAM. Other embodiments include cache memory  340  and a main memory unit  322  that can be any one of the following types of memory: Static random access memory (SRAM), Burst SRAM or SynchBurst SRAM (BSRAM); Dynamic random access memory (DRAM); Fast Page Mode DRAM (FPM DRAM); Enhanced DRAM (EDRAM), Extended Data Output RAM (EDO RAM); Extended Data Output DRAM (EDO DRAM); Burst Extended Data Output DRAM (BEDO DRAM); Enhanced DRAM (EDRAM); synchronous DRAM (SDRAM); JEDEC SRAM; PC100 SDRAM; Double Data Rate SDRAM (DDR SDRAM); Enhanced SDRAM (ESDRAM); SyncLink DRAM (SLDRAM); Direct Rambus DRAM (DRDRAM); Ferroelectric RAM (FRAM); or any other type of memory. Further embodiments include a central processing unit  321  that can access the main memory  322  via: a system bus  350 ; a memory port  303 ; or any other connection, bus or port that allows the processor  321  to access memory  322 . 
     One embodiment of the computing device  200 / 300  provides support for any one of the following installation devices  216 : a CD-ROM drive, a CD-R/RW drive, a DVD-ROM drive, tape drives of various formats, USB device, a bootable medium, a bootable CD, a bootable CD for GNU/Linux distribution such as KNOPPIX®, a hard-drive or any other device suitable for installing applications or software. Applications can in some embodiments include a client agent  220 , or any portion of a client agent  220 . The computing device  200 / 300  may further include a storage device  228  that can be either one or more hard disk drives, or one or more redundant arrays of independent disks; where the storage device is configured to store an operating system, software, programs applications, or at least a portion of the client agent  220 . A further embodiment of the computing device  200 ,  300  includes an installation device  216  that is used as the storage device  228 . 
     The computing device  200 ,  300  may further include a network interface  218  to interface to a Local Area Network (LAN), Wide Area Network (WAN) or the Internet through a variety of connections including, but not limited to, standard telephone lines, LAN or WAN links (e.g., 802.11, T1, T3, 56 kb, X.25, SNA, DECNET), broadband connections (e.g., ISDN, Frame Relay, ATM, Gigabit Ethernet, Ethernet-over-SONET), wireless connections, or some combination of any or all of the above. Connections can also be established using a variety of communication protocols (e.g., TCP/IP, IPX, SPX, NetBIOS, Ethernet, ARCNET, SONET, SDH, Fiber Distributed Data Interface (FDDI), RS232, RS485, IEEE 802.11, IEEE 802.11a, IEEE 802.11b, IEEE 802.11g, CDMA, GSM, WiMax and direct asynchronous connections). One version of the computing device  200 ,  300  includes a network interface  218  able to communicate with additional computing devices  200 ′,  300 ′ via any type and/or form of gateway or tunneling protocol such as Secure Socket Layer (SSL) or Transport Layer Security (TLS), or the Citrix Gateway Protocol manufactured by Citrix Systems, Inc. Versions of the network interface  218  can comprise any one of: a built-in network adapter; a network interface card; a PCMCIA network card; a card bus network adapter; a wireless network adapter; a USB network adapter; a modem; or any other device suitable for interfacing the computing device  200 ,  300  to a network capable of communicating and performing the methods and systems described herein. 
     Embodiments of the computing device  200 ,  300  include any one of the following I/O devices  230   a - 230   n : a keyboard  226 ; a pointing device  227 ; mice; trackpads; an optical pen; trackballs; microphones; drawing tablets; video displays; speakers; inkjet printers; laser printers; and dye-sublimation printers; or any other input/output device able to perform the methods and systems described herein. An I/O controller  223  may in some embodiments connect to multiple I/O devices  230   a - 230   n  to control the one or more I/O devices. Some embodiments of the I/O devices  230   a - 230   n  may be configured to provide storage or an installation medium  216 , while others may provide a universal serial bus (USB) interface for receiving USB storage devices such as the USB Flash Drive line of devices manufactured by Twintech Industry, Inc. Still other embodiments include an I/O device  230  that may be a bridge between the system bus  250  and an external communication bus, such as: a USB bus; an Apple Desktop Bus; an RS-232 serial connection; a SCSI bus; a FireWire bus; a FireWire 800 bus; an Ethernet bus; an AppleTalk bus; a Gigabit Ethernet bus; an Asynchronous Transfer Mode bus; a HIPPI bus; a Super HIPPI bus; a SerialPlus bus; a SCI/LAMP bus; a FibreChannel bus; or a Serial Attached small computer system interface bus. 
     In some embodiments, the computing machine  200 ,  300  can connect to multiple display devices  224   a - 224   n , in other embodiments the computing device  100  can connect to a single display device  224 , while in still other embodiments the computing device  200 ,  300  connects to display devices  224   a - 224   n  that are the same type or form of display, or to display devices that are different types or forms. Embodiments of the display devices  224   a - 224   n  can be supported and enabled by the following: one or multiple I/O devices  230   a - 230   n ; the I/O controller  223 ; a combination of I/O device(s)  230   a - 230   n  and the I/O controller  223 ; any combination of hardware and software able to support a display device  224   a - 224   n ; any type and/or form of video adapter, video card, driver, and/or library to interface, communicate, connect or otherwise use the display devices  224   a - 224   n . The computing device  200 ,  300  may in some embodiments be configured to use one or multiple display devices  224 A- 224 N, these configurations include: having multiple connectors to interface to multiple display devices  224 A- 224 N; having multiple video adapters, with each video adapter connected to one or more of the display devices  224 A- 224 N; having an operating system configured to support multiple displays  224 A- 224 N; using circuits and software included within the computing device  200  to connect to and use multiple display devices  224 A- 224 N; and executing software on the main computing device  200  and multiple secondary computing devices to enable the main computing device  200  to use a secondary computing device&#39;s display as a display device  224 A- 224 N for the main computing device  200 . Still other embodiments of the computing device  200  may include multiple display devices  224 A- 224 N provided by multiple secondary computing devices and connected to the main computing device  200  via a network. 
     In some embodiments, the computing machine  200  can execute any operating system, while in other embodiments the computing machine  200  can execute any of the following operating systems: versions of the MICROSOFT WINDOWS operating systems such as WINDOWS 3.x; WINDOWS 95; WINDOWS 98; WINDOWS 2000; WINDOWS NT 3.51; WINDOWS NT 4.0; WINDOWS CE; WINDOWS XP; and WINDOWS VISTA; the different releases of the Unix and Linux operating systems; any version of the MAC OS manufactured by Apple Computer; OS/2, manufactured by International Business Machines; any embedded operating system; any real-time operating system; any open source operating system; any proprietary operating system; any operating systems for mobile computing devices; or any other operating system. In still another embodiment, the computing machine  200  can execute multiple operating systems. For example, the computing machine  200  can execute PARALLELS or another virtualization platform that can execute or manage a virtual machine executing a first operating system, while the computing machine  200  executes a second operating system different from the first operating system. 
     The computing machine  200  can be embodied in any one of the following computing devices: a computing workstation; a desktop computer; a laptop or notebook computer; a server; a handheld computer; a mobile telephone; a portable telecommunication device; a media playing device; a gaming system; a mobile computing device; a netbook; a device of the IPOD family of devices manufactured by Apple Computer; any one of the PLAYSTATION family of devices manufactured by the Sony Corporation; any one of the Nintendo family of devices manufactured by Nintendo Co; any one of the XBOX family of devices manufactured by the Microsoft Corporation; or any other type and/or form of computing, telecommunications or media device that is capable of communication and that has sufficient processor power and memory capacity to perform the methods and systems described herein. In other embodiments the computing machine  100  can be a mobile device such as any one of the following mobile devices: a JAVA-enabled cellular telephone or personal digital assistant (PDA), such as the i55sr, i58sr, i85s, i88s, i90c, i95c1, or the im1100, all of which are manufactured by Motorola Corp; the 6035 or the 7135, manufactured by Kyocera; the i300 or i330, manufactured by Samsung Electronics Co., Ltd; the TREO 180, 270, 600, 650, 680, 700p, 700w, or 750 smart phone manufactured by Palm, Inc; any computing device that has different processors, operating systems, and input devices consistent with the device; or any other mobile computing device capable of performing the methods and systems described herein. In still other embodiments, the computing device  200  can be any one of the following mobile computing devices: any one series of Blackberry, or other handheld device manufactured by Research In Motion Limited; the iPhone manufactured by Apple Computer; Palm Pre; a Pocket PC; a Pocket PC Phone; or any other handheld mobile device. 
     In some embodiments, the computing device  200  may have different processors, operating systems, and input devices consistent with the device. For example, in one embodiment, the computing device  200  is a TREO 180, 270, 600, 650, 680, 700p, 700w, or 750 smart phone manufactured by Palm, Inc. In some of these embodiments, the TREO smart phone is operated under the control of the PalmOS operating system and includes a stylus input device as well as a five-way navigator device. 
     In other embodiments the computing device  200  is a mobile device, such as a JAVA-enabled cellular telephone or personal digital assistant (PDA), such as the i55sr, i58sr, i85s, i88s, i90c, i95c1, or the im1100, all of which are manufactured by Motorola Corp. of Schaumburg, Ill., the 6035 or the 7135, manufactured by Kyocera of Kyoto, Japan, or the i300 or i330, manufactured by Samsung Electronics Co., Ltd., of Seoul, Korea. In some embodiments, the computing device  200  is a mobile device manufactured by Nokia of Finland, or by Sony Ericsson Mobile Communications AB of Lund, Sweden. 
     In still other embodiments, the computing device  200  is a Blackberry handheld or smart phone, such as the devices manufactured by Research In Motion Limited, including the Blackberry 7100 series, 8700 series, 7700 series, 7200 series, the Blackberry 7520, or the Blackberry Pearl 8100. In yet other embodiments, the computing device  200  is a smart phone, Pocket PC, Pocket PC Phone, or other handheld mobile device supporting Microsoft Windows Mobile Software. Moreover, the computing device  200  can be any workstation, desktop computer, laptop or notebook computer, server, handheld computer, mobile telephone, any other computer, or other form of computing or telecommunications device that is capable of communication and that has sufficient processor power and memory capacity to perform the operations described herein. 
     In some embodiments, the computing device  200  is a digital audio player. In one of these embodiments, the computing device  200  is a digital audio player such as the Apple IPOD, IPOD Touch, IPOD NANO, and IPOD SHUFFLE lines of devices, manufactured by Apple Computer of Cupertino, Calif. In another of these embodiments, the digital audio player may function as both a portable media player and as a mass storage device. In other embodiments, the computing device  200  is a digital audio player such as the DigitalAudioPlayer Select MP3 players, manufactured by Samsung Electronics America, of Ridgefield Park, N.J., or the Motorola m500 or m25 Digital Audio Players, manufactured by Motorola Inc. of Schaumburg, Ill. In still other embodiments, the computing device  200  is a portable media player, such as the Zen Vision W, the Zen Vision series, the Zen Portable Media Center devices, or the Digital MP3 line of MP3 players, manufactured by Creative Technologies Ltd. In yet other embodiments, the computing device  200  is a portable media player or digital audio player supporting file formats including, but not limited to, MP3, WAV, M4A/AAC, WMA Protected AAC, AIFF, Audible audiobook, Apple Lossless audio file formats and .mov, .m4v, and .mp4 MPEG-4 (H.264/MPEG-4 AVC) video file formats. 
     In some embodiments, the computing device  200  comprises a combination of devices, such as a mobile phone combined with a digital audio player or portable media player. In one of these embodiments, the computing device  200  is a Motorola RAZR or Motorola ROKR line of combination digital audio players and mobile phones. In another of these embodiments, the computing device  200  is an iPhone smartphone, manufactured by Apple Computer of Cupertino, Calif. While  FIGS. 1-3  may be described with respect to specific examples of hardware and/or software that may be used, such examples are in no way limiting, but instead are merely illustrative of the type of resources that may be utilized as technology progresses. 
       FIGS. 1-3  show a high-level architecture of an illustrative desktop virtualization system. As shown, the desktop virtualization system may be single-server or multi-server system, or cloud system, including at least one virtualization server  106  configured to provide virtual desktops and/or virtual applications to one or more client access devices  140 . As used herein, a desktop refers to a graphical environment or space in which one or more applications may be hosted and/or executed. A desktop may include a graphical shell providing a user interface for an instance of an operating system in which local and/or remote applications can be integrated. Applications, as used herein, are programs that execute after an instance of an operating system (and, optionally, also the desktop) has been loaded. Each instance of the operating system may be physical (e.g., one operating system per device) or virtual (e.g., many instances of an OS running on a single device). Each application may be executed on a local device, or executed on a remotely located device (e.g., remoted). 
     Illustrated in  FIG. 4  is one embodiment of a computer device  401  configured as a virtualization server in a virtualization environment, for example, a single-server, multi-server, or cloud computing environment. The virtualization server  401  illustrated in FIG.  1  can be deployed as and/or implemented by one or more embodiments of the server  106  illustrated in  FIG. 1  or the computing devices  200  and  300  illustrated in  FIGS. 2 and 3 . Included in virtualization server  401  is a hardware layer that can include one or more physical disks  404 , one or more physical devices  406 , one or more physical processors  408  and a physical memory  416 . In some embodiments, firmware  412  can be stored within a memory element in the physical memory  416  and can be executed by one or more of the physical processors  408 . The virtualization server  401  may further include an operating system  414  that may be stored in a memory element in the physical memory  416  and executed by one or more of the physical processors  408 . Still further, a hypervisor  402  may be stored in a memory element in the physical memory  416  and can be executed by one or more of the physical processors  408 . Executing on one or more of the physical processors  408  may be one or more virtual machines  432 A-C (generally  432 ). Each virtual machine  432  may have a virtual disk  426 A-C and a virtual processor  428 A-C. In some embodiments, a first virtual machine  432 A may execute, on a virtual processor  428 A, a control program  420  that includes a tools stack  424 . In other embodiments, one or more virtual machines  432 B-C can executed, on a virtual processor  428 B-C, a guest operating system  430 A-B. 
     Further referring to  FIG. 4 , and in more detail, the virtualization server  401  may include a hardware layer  410  with one or more pieces of hardware that communicate with the virtualization server  401 . In some embodiments, the hardware layer  410  can include one or more physical disks  404 , one or more physical devices  406 , one or more physical processors  408 , and one or more memory  416 . Physical components  404 ,  406 ,  408 , and  416  may include, for example, any of the components described above in  FIGS. 1-3 . For instance, physical disks  404  may include permanent memory storage, temporary memory storage, disk drives (e.g. optical, floppy, tape), hard disks, external hard drives, flash memory, network-attached storage, a storage-area network, or any other storage repository that the virtualization server  401  can access. Physical devices  406  may include any device included in the virtualization server  401  and/or any combination of devices included in the virtualization server  401  and external devices that communicate with the virtualization server  401 . A physical device  406  may be, for example, a network interface card, a video card, a keyboard, a mouse, an input device, a monitor, a display device, speakers, an optical drive, a storage device, a universal serial bus connection, a printer, a scanner, a network element (e.g., router, firewall, network address translator, load balancer, virtual private network (VPN) gateway, Dynamic Host Configuration Protocol (DHCP) router, etc.), or any device connected to or communicating with the virtualization server  401 . The physical memory  416  in the hardware layer  410  may include any type of memory. The physical memory  416  may store data, and in some embodiments may store one or more programs, or set of executable instructions.  FIG. 4  illustrates an embodiment where firmware  412  is stored within the physical memory  416  of the virtualization server  401 . Programs or executable instructions stored in the physical memory  416  can be executed by the one or more processors  408  of the virtualization server  401 . 
     Virtualization server  401  may also include a hypervisor  402 . In some embodiments, hypervisor  402  may be a program executed by processors  408  on the virtualization server  401  to create and manage any number of virtual machines  432 . The hypervisor  402  can be referred to as a virtual machine monitor, or platform virtualization software. In some embodiments, a hypervisor  402  can be any combination of executable instructions and hardware that monitors virtual machines executing on a computing machine. Hypervisor  402  may be Type 2 hypervisor, or a hypervisor that executes within an operating system  414  executing on the virtualization server  401 . A Type 2 hypervisor, in some embodiments, executes within an operating system  414  environment and virtual machines execute at a level above the hypervisor. In many embodiments, the Type 2 hypervisor executes within the context of a user&#39;s operating system such that the Type 2 hypervisor interacts with the user&#39;s operating system. In other embodiments, one or more virtualization servers  401  in a virtualization environment may include a Type 1 hypervisor (Not Shown). A Type 1 hypervisor may execute on the virtualization server  401  by directly accessing the hardware and resources within the hardware layer  410 . That is, while a Type 2 hypervisor  402  accesses system resources through a host operating system  414 , a Type 1 hypervisor may directly access all system resources without needing a host operating system  414 . A Type 1 hypervisor may execute directly on one or more physical processors of  408  the virtualization server  401 , and may include program data stored in the physical memory  416 . 
     The hypervisor  402 , in some embodiments, can provide virtual resources to operating systems  430  or control programs  420  executing on virtual machines  432  in any manner that simulates the operating systems  430  or control programs  420  having direct access to system resources. System resources can include: physical devices  406 ; physical disks; physical processors; physical memory  416  and any other component included in the virtualization server  401  hardware layer  410 . In these embodiments, the hypervisor  402  may be used to emulate virtual hardware, partition physical hardware, virtualize physical hardware, or execute virtual machines that provide access to computing environments. In still other embodiments, the hypervisor  402  controls processor scheduling and memory partitioning for a virtual machine  432  executing on the virtualization server  401 . Hypervisor  402  may include those manufactured by VMWare, Inc., of Palo Alto, Calif.; the XEN hypervisor, an open source product whose development is overseen by the open source Xen.org community; HyperV, VirtualServer or virtual PC hypervisors provided by Microsoft, or others. In some embodiments, a virtualization server  401  executes a hypervisor  402  that creates a virtual machine platform on which guest operating systems may execute. In these embodiments, the virtualization server  401  can be referred to as a host server. An example of such a virtualization server is the XEN SERVER provided by Citrix Systems, Inc., of Fort Lauderdale, Fla. 
     The hypervisor  402  may create one or more virtual machines  432 B-C (generally  432 ) in which guest operating systems  430  execute. In some embodiments, the hypervisor  402  may load a virtual machine image to create a virtual machine  432 . In other embodiments, the hypervisor  402  may executes a guest operating system  430  within the virtual machine  432 . In still other embodiments, the virtual machine  432  may execute the guest operating system  430 . 
     In addition to creating virtual machines  432 , the hypervisor  402  may control the execution of at least one virtual machine  432 . In other embodiments, the hypervisor  402  may presents at least one virtual machine  432  with an abstraction of at least one hardware resource provided by the virtualization server  401  (e.g., any hardware resource available within the hardware layer  410 ). In other embodiments, the hypervisor  402  may control the manner in which virtual machines  432  access the physical processors  408  available in the virtualization server  401 . Controlling access to the physical processors  408  may include determining whether a virtual machine  432  should have access to a processor  408 , and how physical processor capabilities are presented to the virtual machine  432 . 
     As shown in the example of  FIG. 4 , the virtualization server  401  may host or execute one or more virtual machines  432 . A virtual machine  432  is a set of executable instructions that, when executed by a processor  408 , imitate the operation of a physical computer such that the virtual machine  432  can execute programs and processes much like a physical computing device. While  FIG. 4  illustrates an embodiment where a virtualization server  401  hosts three virtual machines  432 , in other embodiments the virtualization server  401  can host any number of virtual machines  432 . The hypervisor  402 , in some embodiments, provides each virtual machine  432  with a unique virtual view of the physical hardware, memory, processor and other system resources available to that virtual machine  432 . In some embodiments, the unique virtual view can be based on any of the following: virtual machine permissions; application of a policy engine to one or more virtual machine identifiers; the user accessing a virtual machine; the applications executing on a virtual machine; networks accessed by a virtual machine; or any other similar criteria. For instance, the hypervisor  402  may create one or more unsecure virtual machines  432  and one or more secure virtual machines  432 . Unsecure virtual machines  432  may be prevented from accessing resources, hardware, memory locations, and programs that secure virtual machines  432  may be permitted to access. In other embodiments, the hypervisor  402  may provide each virtual machine  432  with a substantially similar virtual view of the physical hardware, memory, processor and other system resources available to the virtual machines  432 . 
     Each virtual machine  432  may include a virtual disk  426 A-C (generally  426 ) and a virtual processor  428 A-C (generally  428 .) The virtual disk  426 , in some embodiments, is a virtualized view of one or more physical disks  404  of the virtualization server  401 , or a portion of one or more physical disks  404  of the virtualization server  401 . The virtualized view of the physical disks  404  can be generated, provided and managed by the hypervisor  402 . In some embodiments, the hypervisor  402  provides each virtual machine  432  with a unique view of the physical disks  404 . Thus, in these embodiments, the virtual disk  426  included in each virtual machine  432  can be unique when compared with the other virtual disks  426 . 
     A virtual processor  428  can be a virtualized view of one or more physical processors  408  of the virtualization server  401 . In some embodiments, the virtualized view of the physical processors  408  can be generated, provided and managed by the hypervisor  402 . In some embodiments, the virtual processor  428  has substantially all of the same characteristics of at least one physical processor  408 . In other embodiments, the virtual processor  408  provides a modified view of the physical processors  408  such that at least some of the characteristics of the virtual processor  428  are different than the characteristics of the corresponding physical processor  408 . 
       FIG. 5  illustrates an example of a cloud-based virtualization system  500 . As seen in  FIG. 5 , system  500  may be a virtualization server such as server  401 . System  500  includes a trusted server domain  501  (e.g., virtual machine  432 A) and a guest domain  511  (e.g., virtual machine  432 B) executing on a hypervisor  521  (e.g., hypervisor  402  and/or operating system  414 , depending on whether the virtualization system is a type 1 or type 2 hypervisor system). Each of trusted domain  501  and guest domain  511  may include a corresponding kernel  502 ,  512  and file system  503 ,  513 . Virtualization system  500  may include other guest domains as well. However, for ease of understanding and for illustrative purposes, only a single guest domain is shown. Trusted domain  501  may also be referred to as domain zero (Dom 0), and may perform management and administrative functions of the virtualization system  500  in order to effect the ability of virtualization system  500  to execute one or more guest domains. 
     Trusted server domain  501  may include a key value store (also referred to as a key value database)  507  administered by a key value manager  506 . Key value store  507  may be an implementation of XenStore™ by Citrix Systems Inc. of Fort Lauderdale, Fla. XenStore™ is an information storage space shared between domains, and may be used to share configuration, metadata and status information. Each guest domain may get its own path in the key value store. When values are changed in the key value store, the corresponding driver  516  is notified. The key value store may be a shared hierarchical key value store, or may be any other type of key value store or registry. 
     Trusted server domain  501  may further include a file  504  within file system  503  that is to be shared with guest domain  511  via daemon  505 . Daemon  505  may transfer data back and forth with guest domain  511  via first shared memory  531 , which is also accessible by proxy driver  515  of guest domain  511 , as further described below. Proxy driver  515  may be installed during an update process, such as Windows Update, by a network administrator, during an installation process, or via any other known or developed technique. Guest domain  511  may further include key value database monitor  516  that monitors updates to the key value database via second shared memory  532 . Monitor  516  may be a driver separate from proxy driver  515 . When monitor  516  detects a change to the key value database indicating that one or more files are available, monitor  516  may update database  518  of proxy driver  515 . Database  518  stores a local record of files made available by trusted domain  501 , so that proxy driver  515  can determine whether to make a file system call to local file system  513  or to file system  503  of trusted domain  501 . Shared memory  531 ,  532  may be the same or different portions of physical memory. 
     Proxy driver  515  maintains database  518  and acts to intercept calls made by any application or program executing within guest domain  511  to access the guest domain&#39;s file system  513 . Database  518  stores metadata information regarding files available from trusted domain  501  rather than from guest domain  511 . When the desired file is located within file system  513 , the file system call may be sent to file system  513  as normal. However, when the desired file is actually a file shared by trusted domain  501 , proxy driver  515  proxies the request to trusted domain  501  via shared memory  531  as further described below. Metadata regarding files available in trusted domain  501  may be received via key value database  507  and shared memory  532 , whereas file contents may be received via shared memory  531  as further described herein. 
     Shared memory  531  may be a page or pages of memory allocated to or by guest domain  511  that guest domain  511  makes available to one or more other domains, e.g., to trusted domain  501 . Guest domain  511  grants rights to trusted domain  501  to access shared memory  531 , e.g., using Grant Tables, by indicating in key value database  507  which pages are available to trusted domain  501 , and/or by instructing hypervisor  521  to grant permission to trusted domain  501  to have read/write access to that page or pages of memory. Thus, when guest domain  511  shares a page or pages of memory with another domain, hypervisor  521  (or system  500 ) permits access to those pages by the other domain. 
     Memory  531 ,  532  may be shared as a circular ring or buffer. Each of the sharer (guest domain  511 ) and sharee (trusted domain  501 ) may maintain a pointer to its corresponding last read/write position in the shared memory, where the pointer moves back to the first memory location in the page after consuming the last memory location in the page. According to one aspect, when a guest domain shares a page or pages of memory, the guest domain may also allocate, designate, and/or store one or more pointers in the shared memory for use by each of the sharer (guest domain) and sharee (trusted domain) to maintain a current or last read location within the shared memory. Thus, each of the sharer and sharee can read the pointer of the other domain and ensure that one domain does not overwrite data not yet read by the other domain (e.g., does not “lap” the other domain). In another possible embodiment, pointer locations may be updated in key value database  507  so that one domain never overwrites data that has not yet been consumed by the other domain. Hypercalls may be used to as necessary to access desired information or request specific resources. A hypercall is a software trap from a domain to the hypervisor, just as a syscall is a software trap from an application to the kernel or OS. Domains may use hypercalls to request privileged operations such as updating page tables. Like a syscall, a hypercall is synchronous, but the return path from the hypervisor to the domain may use event channels. An event channel is a queue of asynchronous notifications, and notify of the same sorts of events that interrupts notify on native hardware. An event channel may be used, e.g., by each domain to notify the other domain when there is new data written to shared memory for the other domain to retrieve. 
     Methods for performing trusted file indirection will now be described with further reference to  FIG. 6  and  FIG. 7 . Trusted file indirection, generally, is the process of safely injecting one or more files into a file system of a guest domain from a trusted domain. Trusted file indirection may be used, e.g., to allow one domain access to a file in the file system of another, trusted domain, without breaching security of the trusted domain. File indirection may be useful, e.g., to apply hotfixes and inject other files into guest domains, rather than requiring comprehensive tools to be installed on the guest domain. Thus, trusted file indirection may be used instead of installing an ISO image or other utilities to perform hotfixes and updates. 
       FIG. 6  illustrates a method for updating a database storing shared file information and notifying other domains about the shared file information. Initially, in step  601 , trusted domain  501  receives one or more files  504  in one or more directories that are to be shared with guest domain  511 . The files may be placed in file system  503  by a system administrator, by an automated update routine (e.g., similar to Windows® Update), or by any other desired means. In step  603 , key value manager  506  updates key value database  507  to reflect the one or more domains with which the files are to be shared. The key value manager  506  may also update key value store  507  with metadata regarding the available files, e.g., file name, extension, size, modification date, creation date, etc. In step  605 , key value monitor  516  residing in guest domain  511  monitors for changes to key value store that are directed to guest domain  511 . When changes are detected, key value monitor in step  607  updates file system DB  518  within proxy driver  515  to reflect the availability of the one or more files (and/or directories). The method then ends, and may be repeated when additional shared file(s) are stored in trusted domain  501 . 
       FIG. 7  illustrates a method for intercepting file system calls to provide guest domain  511  with access to shared files stored on trusted domain  501 . In step  709  proxy driver  515  intercepts a file system call by an application or program executing within guest domain  511 . The file system call may be a read, write, directory listing, file open, or any other file system call. In step  711  proxy driver  515  queries database  518  to determine whether the requested data is stored locally within file system  513 , or externally in file system  503  associated with trusted domain  501 . In step  713 , when the requested data is stored locally within file system  513 , proxy driver  515  sends the file system command to file system  513  for execution, and the results are returned to proxy driver  515  in step  719 . If the requested data is stored in file system  503  of trusted domain  501 , then in step  715  proxy driver  515  sends the file system call to trusted domain  501  by placing the file system call in shared memory  531 . 
     After receiving the file system call, in step  717  daemon  505  on trusted domain  501  executes the file system call on file system  503 . For example, when the file system call is a write command, daemon  505  may write to file  504 . When the file system call is a read comment, daemon  505  may fetch data from file  504 . In step  719  daemon  505  returns the results of the file system call to proxy driver  515  by placing the results in shared memory  531 . In step  719  proxy driver  515  retrieves and/or receives the file system call result. When the file system call is a write command, the results may include a success acknowledgement. When the file system call is a read command, the results may include all or a portion of the read data, e.g., streamed through shared memory  531  as data is retrieved by daemon  505  and received by proxy driver  515 . After the file system call is completed by either daemon  505  or file system  513 , in step  721  proxy driver  515  responds to the entity from which the original file system call was received in step  709 . 
     Various steps of the above method may be combined, split, or reordered to accomplish a similar result. Using a method similar to that described above, a trusted domain can inject one or more files (and/or directories) into a guest domain so that the data appears to be within the local file system of the guest domain, when in fact the data resides within another domain sharing the data. For example, when guest domain  511  makes a file system call requesting information to present in a file directory, e.g., within Windows Explorer, proxy driver  515  may combine information available from both local file system  513  and trusted domain file system  503  to enumerate and present a single file structure that appears unified, or may alternatively enumerate and present files from trusted domain  501  to appear in a separate directory or location from those files located in guest domain file system  513 . When a user requests a file from the directory or location corresponding to trusted domain  501 , proxy driver  515  actually proxies that request to trusted domain  501  using a method such as that described above with respect to  FIG. 7 . Data can thus “appear” to be within a guest domain&#39;s file system, when in fact the data resides in a different domain, even when the guest domain has no network connection and without emulating any virtual hardware (e.g., mounting a virtual CD-ROM, DVD, or other mountable file storage). 
     Various modifications may be made to implement trusted file indirection using slightly different techniques. For example, instead of shared memory, all data may be passed through the key value store. However, key value store transfers may be slower than using directly accessed shared memory. In another alternative, a single shared memory may be used for all transfers, rather than separate shared memory  531 ,  532 . In some embodiments, techniques described herein may be used to emulate a disk in the guest domain. However, disk emulation may be under operating system control and can introduce unnecessary complexities resulting from not being able to trap requests using proxy driver  515 . In yet other embodiments, file transfer may occur over a shared network volume. However, network security issues must then be taken into account, and guest domain network access may be blocked according to user security settings. 
     Aspects of the disclosure have been described in terms of illustrative embodiments thereof. Numerous other embodiments, modifications, and variations within the scope and spirit of the appended claims will occur to persons of ordinary skill in the art from a review of this disclosure. For example, one of ordinary skill in the art will appreciate that the steps illustrated in the illustrative figures may be performed in other than the recited order, and that one or more steps illustrated may be optional in accordance with aspects of the disclosure. Modifications may be made by those skilled in the art, particularly in light of the foregoing teachings. For example, each of the elements of the aforementioned embodiments may be utilized alone or in combination or sub-combination with elements of the other embodiments. It will also be appreciated and understood that modifications may be made without departing from the spirit and scope of the following claims.