EXTENSION POINT DECLARATIVE REGISTRATION FOR VIRTUALIZATION

BACKGROUND

[0001] Virtualization refers to the execution of a virtual machine by physical hardware
and then running operating systems and/or applications virtually on the virtual machine.
The virtual machine may represent a least common denominator of hardware functionality
or may represent a well-known configuration for which it is easy to prepare an operating
system and applications. Many data centers use virtualization to be able to easily move a
virtual machine to new physical hardware as resource requirements increase, for
maintenance cycles, and to balance physical server loads. Virtualization is useful for
many situations, but can also impose limitations that occur due to many virtual machines
contending for the same resources (e.g., central processing unit (CPU), memory, and
network interface card (NIC)).

[0002] Application virtualization provides a virtual machine at the level of a single
application. For example, a host operating system may natively run some applications,
while providing a virtual environment for running others. This may allow the operating
system, for example, to run applications designed for a different operating system.
Application virtualization blurs the distinction for the user between applications running
natively in the host operating system and applications running in a virtual machine. For
example, both types of applications may appear side by side in a taskbar or menu provides
by the operating system shell. MICROSOFT Application Virtualization (App-V), for
example, transforms applications into centrally managed virtual services that are not
installed and do not conflict with other applications. In a physical environment, every
application depends on its operating system (OS) for a range of services, including
memory allocation, device drivers, and much more. Incompatibility between an
application and its OS can be addressed by either server virtualization or presentation
virtualization—but for incompatibility between two applications installed on the same
instance of an OS is solved by application virtualization.
[0003] Operating systems need to have their behaviors modified to fit the needs of
customers. For example, the user may install MICROSOFT Word, which registers a file
type association. This file type association changes how the operating system behaves.
When the user clicks on a document with the Word file type association, the operating
system invokes MICROSOFT Word. File type associations are a specific example of an
operating system extension point. One part of virtualization is isolation, meaning one
application cannot see another application and that one application's actions do not affect
the operating system, or only affect the operating system through a proxy. In the file type
association case, one example of a proxy is the MICROSOFT App-V client that detects
and registers the file type association as a proxy on behalf of the application. In this way,
MICROSOFT App-V is aware of the operating system modification and can reverse it
when the virtualized application is removed.
[0004] Unfortunately, building a custom proxy for each operating system extension point
is not practical or scalable. There are over 3000 extension points in
MICROSOFTWINDOWS, making it virtually impossible to write a proxy for each one.
Moreover, with support for each new operating system, additional extension points need to
be detected and managed to keep application virtualization working as expected. The
constantly expanding number of extension points consumes development and testing time
and takes time away from other new features.

SUMMARY

[0005] An extension point virtualization system is described herein that uses operating
system-provided reparse points to provide minimal extension point registration. Reparse
points preserve application isolation while removing the scale problem of writing custom
extension point proxies for each extension point. Many extension points can be handled
by redirecting the operating system from a typical location for an application resource to a
virtualized safe location for the application resource. The extension point virtualization
system uses reparse points to eliminate the need for custom proxies for each extension
point. Instead, the system can use a single file system filter that generically handles
application virtualization reparse points, and store reparse point data for extension points
that need redirection. Thus, the system simplifies the process of handling new extension
points by allowing an application virtualization system to simply register new locations
that can be handled with reparse points and to then handle registered locations generically.
[0006] This Summary is provided to introduce a selection of concepts in a simplified form
that are further described below in the Detailed Description. This Summary is not
intended to identify key features or essential features of the claimed subject matter, nor is
it intended to be used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is a block diagram that illustrates components of the extension point
virtualization system, in one embodiment.
[0008] Figure 2 is a flow diagram that illustrates the processing of the extension point
virtualization system to identify extension points and setup application redirection for
identified extension points, in one embodiment.
[0009] Figure 3 is a flow diagram that illustrates the processing of the virtualization
system to respond to a request to access a resource through an extension point, in one
embodiment.

DETAILED DESCRIPTION

[0010] An extension point virtualization system is described herein that uses operating
system-provided reparse points to provide minimal extension point registration. Reparse
points preserve application isolation while removing the scale problem of writing custom
extension point proxies for each extension point. Many extension points can be handled
by redirecting the operating system from a typical location for an application resource to a
virtualized safe location for the application resource. For example, applications that
previously installed files into the operating system directory may be redirected to install
those files into the application's own directory (even though application virtualization
fools the application into thinking the files are still in the operating system directory).
[0011] A file or directory can contain a reparse point, which is a collection of user-defined
data. The format of this data is understood by the application that stores the data and a file
system filter, which an application developer installs to interpret the data and process the
file. When an application sets a reparse point, it stores this data, plus a reparse tag, which
uniquely identifies the data it is storing. When the file system opens a file with a reparse
point, it attempts to find the file system filter associated with the data format identified by
the reparse tag. If a file system filter is found, the filter processes the file as directed by
the reparse data. If a file system filter is not found, the file open operation fails. For
example, reparse points are used to implement NTFS file system links and the
MICROSOFT Remote Storage Server (RSS). RSS uses an administrator-defined set of
rules to move infrequently used files to long-term storage, such as tape or optical media.
RSS uses reparse points to store information about the file in the file system. This
information is stored in a stub file that contains a reparse point whose data points to the
device where the actual file is located. The file system filter can use this information to
retrieve the file. Reparse points are also used to implement mounted folders.
[0012] The extension point virtualization system uses reparse points to eliminate the need
for custom proxies for each extension point. Instead, the system can create a single file
system filter that generically handles application virtualization reparse points, and store
reparse point data for extension points that need redirection. For example, the system can
associate a reparse point with a file or registry key, regardless of the specific extension
purpose of that file or registry key. Thus, the system simplifies the process of handling
new extension points by allowing an application virtualization system to simply register
new locations that can be handled with reparse points and to then handle registered
locations generically.
[0013] Application virtualization gathers up the file and registry data for an application
and places this in a store called a package, making the application think that the files and
registry entries are installed locally, even though they are not. The previous method of
registering extension points created a proxy for each extension point. This proxy would
detect that the package was present on the system, and extract enough metadata to register
the extension point with the operating system. The proxy would be invoked when the
extension point was invoked, find the right package, and hand off the work to that
package. In contrast, the extension point virtualization system described herein uses an
operating system facility, the reparse point (or symbolic link in UNIX), to minimally
register extension points. A reparse point is an operating system facility that tells the
operating system that when a particular path is used in an operating system application programming interface (API), the operating system should instead look to a substitute path
for the data.
[0014] The extension point virtualization system causes the redirection to occur to a
location in virtual package. By doing this, the system provides a way to allow new
extension points to be added without a proxy, while continuing to isolate the application
from the operating system. Take the example of the ".txt" file type association, realizing
this technique works with other types of extension points. The file type association has a
registry key that causes the operating system to run a command line specifying a path to
an executable file when a user clicks on this file type association from the operating
system shell (e.g., MICROSOFTWINDOWS Explorer). In the default case the registry
key data is "HKEY_CLASSES_ROOT\txtfile\shell\open\command=
%SystemRoot%\system3 2\NOTEPAD.EXE %1," which causes the operating system to
run Notepad to open the file. The extension point virtualization system detects that a
package registering the ".txt" file type association is on the system, and places a reparse
point in the registry so that when the shell opens
HKEY_CLASSES_ROOT\txtfile\shell\open\command it will be reparsed to HKCR\[APP
GUID]\ txtfile\shell\open\command. In this case, [APP GUID] is a package-specific
globally unique identifier (GUID).
[0015] This technique can be generalized to other extension points as well as to extension
points that do not include a single registry entry but rather multiple registry entries across
multiple locations, as well as files and directories. The extension point virtualization
system works with the package (which is the data), the application virtualization
environment (e.g., the MICROSOFT App-V client), which performs the registration on
behalf of the package, and a set of extension points. The extension points can be
expressed in a declarative extensible markup language (XML) syntax, so that the
application virtualization environment can easily add new extension points without
requiring modifications to the environment or the package.
[0016] Figure 1 is a block diagram that illustrates components of the extension point
virtualization system, in one embodiment. The system 100 includes an extension point
identification component 110, an extension point data store 120, an application
virtualization environment 130, an extension point registration component 140, a reparse
point creation component 150, an extension point access component 160, and an extension
point redirection component 170. Each of these components is described in further detail
herein.
[0017] The extension point identification component 110 identifies extension points
through which an operating system or application can be extended by third party
programmatic code. For example, the component may detect a registry key through which
application add-ins can be registered to be invoked by the application. In some cases,
extension points are identified manually by process monitoring or other tools used by an
administrator to watch an application's behavior as the application runs. For example, the
administrator can use a registry monitoring locations to determine the registry locations
read by an application or the operating system.
[0018] The extension point data store 120 stores identified extension points in a
declarative format. The extension point data store 120 may include a file (e.g., an XML
file), a database, a network-based data store, a cloud-based storage service, or other
storage medium from which a list of identified extension points can be retrieved. An
administrator or application environment author may add new extension points over time
as they are discovered, so that even previously deployed virtualized applications can
benefit from increased operating system isolation by protection from modifications to the
operating system previously undetected by the application environment. In addition,
independent software vendors (ISVs) may contribute lists of their own application
extension points for addition to the data store 1 0 so that applications that modify their
applications can be more easily virtualized and isolated.
[0019] The application virtualization environment 130 provides a level of indirection
between the virtual application and the host operating system. The wrapper may be very
thin allowing the application to run nearly natively, such as when the application is
designed to run on the host operating system. Alternatively or additionally, the wrapper
may provide APIs and satisfy other constraints expected by applications designed for other
operating systems or operating system versions. Thus, the application virtualization
environment 130 provides a virtual application with the environment for which the
application was designed using the available resources of the host operating system.
[0020] The extension point registration component 140 detects installation of a virtual
application package that references an identified extension point. The component 140
accesses the extension point data store 1 0 to load a list of identified extension points and
compares the list to packages invoked by a user. If a match is found, the component 140
invokes the reparse point creation component 150 to create a reparse point redirecting the
application to look for the extension point data within the application package.
[0021] The reparse point creation component 150 creates a reparse point for an identified
extension point and the detected virtual application package that references the identified
extension point. For example, if the extension point registration component 140 detects a
package registering a file type association, then the reparse point creation component 150
creates a reparse point for the registry entry within the file type association that describes
the application to launch when the file type association is invoked. The created reparse
point redirects the registry entry to a location within the detected virtual application
package.
[0022] The extension point access component 160 detects access of the created reparse
point and invokes the extension point redirection component 170 to cause the operating
system to look for specified data in a location associated with the detected virtual
application package. Although described as a separate component, the extension point
virtualization system 100 may rely on default operating system behavior to allow the
operating system to perform the redirection without informing the extension point
virtualization system 100. However, the operating system does allow registration of a file
system filter that is invoked when a reparse point is accessed and the system may, in some
embodiments, use this functionality to detect access and perform custom handling. This
may be useful, for example, for debugging and auditing where application requests are
being redirected.
[0023] The extension point redirection component 170 causes the operating system or an
application to look for specified data referenced by a reparse point in a location associated
with the detected virtual application package. As noted previously, the extension point
virtualization system 100 may rely on default behavior of the operating system to perform
the redirection as a function of the reparse point without involving the extension point
virtualization system 100.
[0024] The computing device on which the extension point virtualization system is
implemented may include a central processing unit, memory, input devices (e.g., keyboard
and pointing devices), output devices (e.g., display devices), and storage devices (e.g.,
disk drives or other non-volatile storage media). The memory and storage devices are
computer-readable storage media that may be encoded with computer-executable
instructions (e.g., software) that implement or enable the system. In addition, the data
structures and message structures may be stored or transmitted via a data transmission
medium, such as a signal on a communication link. Various communication links may be
used, such as the Internet, a local area network, a wide area network, a point-to-point dialup
connection, a cell phone network, and so on.
[0025] Embodiments of the system may be implemented in various operating
environments that include personal computers, server computers, handheld or laptop
devices, multiprocessor systems, microprocessor-based systems, programmable consumer
electronics, digital cameras, network PCs, minicomputers, mainframe computers,
distributed computing environments that include any of the above systems or devices, and
so on. The computer systems may be cell phones, personal digital assistants, smart
phones, personal computers, programmable consumer electronics, digital cameras, and so
on.
[0026] The system may be described in the general context of computer-executable
instructions, such as program modules, executed by one or more computers or other
devices. Generally, program modules include routines, programs, objects, components,
data structures, and so on that perform particular tasks or implement particular abstract
data types. Typically, the functionality of the program modules may be combined or
distributed as desired in various embodiments.
[0027] Figure 2 is a flow diagram that illustrates the processing of the extension point
virtualization system to identify extension points and setup application redirection for
identified extension points, in one embodiment. Beginning in block 10, the system
identifies an extension point. For example, the system may receive a list of extension
points from an operating system vendor or ISV for addition to the extension point data
store. Alternatively or additionally, a virtualization system developer or system
administrator using application virtualization may manually identify extension points,
such as through process monitoring tools.
[0028] Continuing in block 220, the system adds the identified extension point to an
extension point data store. The extension point data store may comprise a declarative
format, such as an XML file, that lists known extension points and associated resource
paths. When the system detects a reference to an extension point path in an application
package, the system performs the steps described herein to isolate and redirect the
application's modification of the operating system. Continuing in decision block 230, if
there are more extension points to identify, then the system loops to block 210, else the
system continues at block 240. Note that although illustrated for ease of explanation in the
same flow diagram, the preceding steps may occur separately from the following steps and
may occur on an ongoing basis as new extension points are discovered. Likewise, the
following steps may occur repeatedly for many applications as each virtualized application
is executed by the system.
[0029] Continuing in block 240, the system receives an application execution request that
specifies a virtual application package. Typically, this occurs when a user runs an
application from the operating system shell that has been setup by an administrator to be
virtualized. The application generally is not even installed on the user's computer but the
user's computer contains a sufficient reference to locate and run the virtual application
package stored centrally (e.g., on a network). When a virtual application package is
invoked, the system runs the application virtualization environment described herein as a
client to guide the application virtualization process.
[0030] Continuing in block 250, the system identifies one or more application extension
point references within the specified virtual application package by comparing one or
more paths referenced by the virtual application package to those in the extension point
data store. For example, an application may register a file type association or a word
processing application add-in through a registry-based extension point. If the registry
location is on the list stored by the extension point data store, then the system determines
that the application package references an extension point. Continuing in decision block
260, if the system detects an extension point reference, then the system continues at block
270, else the system completes.
[0031] Continuing in decision block 270, the system creates a reparse point to redirect an
identified application extension point reference to an isolated location within the specified
virtual application package. The reparse point causes accesses of the extension point to
look for data within the application package and prevents the application package from
modifying the operating system directly. Continuing in decision block 280, if the system
detected additional application extension point references, then the system loops to block
270 to create reparse points for the each additional reference, else the system completes.
After block 280, these steps conclude.
[0032] Figure 3 is a flow diagram that illustrates the processing of the virtualization
system to respond to a request to access a resource through an extension point, in one
embodiment. Beginning in block 310, the system receives a resource access request that
references a resource path. For example, an application may call a file open API provided
by the operating system and specify a path to a file that the application requests to open.
Alternatively or additionally, other applications, such as the operating system shell, may
attempt to access a resource location through which applications can extend the
functionality of the operating system or application.
[0033] Continuing in block 320, the extension point virtualization system detects whether
the resource referenced by the path includes an associated reparse point. For example, the
operating system may look for data associated with the resource where reparse point data
is stored. Continuing in decision block 330, if the system detected a reparse point, then
the system continues at block 340, else the system completes. Continuing in block 340,
the extension point virtualization system identifies a virtual application package associated
with the referenced path. For example, the reparse point may include an application
GUID that identifies the application package. The system may include a common method
of mapping application GUIDs to application packages, such as storing application
packages in a well-known location using the application GUID.
[0034] Continuing in block 350, the extension point virtualization system redirects the
resource request to the identified virtual application package. For example, the operating
system may forward the resource request to a registered file system driver after detecting
the reparse point or handle the request in a default manner, such as by redirecting the
request to a specified location. As an example, the system may replace a file path
contained in the received request with a file path associated with the virtual application
package. Continuing in block 360, the extension point virtualization system responds to
the redirected resource request by providing access to the requested resource. For
example, the operating system may open an identified file and provide the file data in
response to the request. The application behaves as if the data is where the application
normally stores it and the virtualization system modifies requests to point to the location
where the data is actually stored. Because of the redirection performed by the reparse
point, the application virtualization works correctly whether the resource request comes
from the application, another process, or other sources. After block 360, these steps
conclude.
[0035] In some embodiments, the extension point virtualization system stores application
data in a package file format. A package file can be any file format capable of storing
multiple other files and types of data. For example, common existing package file formats
include ZIP, CAB, RAR, SFT, and other similar formats. Package files often include
compression for reducing file size and other features (e.g., encryption) in addition to
allowing multiple files to be stored in one archive format. A package file for a virtualized
application may include registry hives, files, databases, and other types of data that are
used by the virtual application. The operating system may mount the package files like a
directory, a volume, a disk drive, or other resource so that the virtual application can
reference the items stored within the package file using common operating system APIs
for file and other resource manipulation. In some embodiments, the extension point
virtualization system may include virtual application data in the executable of the virtual
application, so that the application can be distributed as a single EXE file with selfextracting
data. Although several examples are described here, the extension point
virtualization system is not limited to any particular manner of storing application data,
and storage mechanisms other than those described can be used to achieve similar results.
[0036] From the foregoing, it will be appreciated that specific embodiments of the
extension point virtualization system have been described herein for purposes of
illustration, but that various modifications may be made without deviating from the spirit
and scope of the invention. Accordingly, the invention is not limited except as by the
appended claims.

CLAIMS

1. A computer-implemented method for identifying extension points and isolating
application use of extension points, the method comprising:
identifying an extension point that provides a manner of extend an operating
system or application through third-party extension;
adding the identified extension point to an extension point data store;
receiving an application execution request that specifies a virtual application
package;

identifying one or more application extension point references within the specified
virtual application package by comparing one or more paths referenced by the virtual
application package to those in the extension point data store; and
creating a reparse point to redirect an identified application extension point
reference to an isolated location within the specified virtual application package,
wherein the preceding steps are performed by at least one processor.

2. The method of claim 1 wherein identifying an extension point comprises receiving
a list of extension points from an operating system vendor or independent software vendor
(ISV).

3. The method of claim 1 wherein identifying an extension point comprises
automatically identifying the extension point a process monitoring tool that detects an
application's use of operating system resources.

4. The method of claim 1 wherein the extension point data store comprises a
declarative format that lists known extension points and associated resource paths.

5. The method of claim 1 wherein receiving an application execution request
comprises receiving a user request to run a virtualized application.

6. The method of claim 1 wherein receiving an application execution request
comprises receiving a request to execute an application that is not natively installed on a
computer system from which the request was received.

7. The method of claim 1 further comprising, upon receiving the application
execution request, invoking an application virtualization environment in which to run the
requested application.

8. The method of claim 1 wherein identifying an extension point reference comprises
identifying a request to register a file type association.

9. The method of claim 1wherein creating a reparse point comprises specifying an
application identifier and an alternative path for accessing the identified application
extension point reference.

10. The method of claim 1wherein creating a reparse point further comprises
preventing the specified virtual application from directly modifying a host operating
system that executes the virtual application.

11. A computer system for generically handling virtualization of operating system and
application extension points, the system comprising:
a processor and memory configured to execute software instructions;
an extension point identification component configured to identify extension points
through which an operating system or application can be extended by third party
programmatic code;
an extension point data store configured to store identified extension points in a
declarative format;
an application virtualization environment configured to provide a level of
indirection between a virtual application and a host operating system;
an extension point registration component configured to detect installation of a
virtual application package that references an identified extension point;
a reparse point creation component configured to create a reparse point for an
identified extension point pointing to the detected virtual application package that
references the identified extension point;
an extension point access component configured to detect access of the created
reparse point and invoke an extension point redirection component; and
an extension point redirection component configured to cause the host operating
system or an application to look for specified data referenced by a reparse point in a
location associated with the detected virtual application package.

12 . The system of claim 11 wherein the extension point identification component is
further configured to automatically identify extension points based on process monitoring
to detect paths accessed by an application during execution.

13. The system of claim 11 wherein the extension point data store comprises an XML
file that includes a list of identified extension points.

14. The system of claim 11 wherein the extension point data store is further configured
to receive new extension points over time as they are discovered, so that previously
deployed virtualized applications can benefit from increased operating system isolation by
protection from modifications to the operating system previously undetected by the
application environment.

15. The system of claim 11 wherein the application virtualization environment is
further configured to provide the virtual application with an environment for which the
application was designed using the available resources of the host operating system.