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VSS_APPLICATION_LEVEL enumeration (vss.h)

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The VSS_APPLICATION_LEVEL enumeration indicates the application level, the point in the course of the creation of a shadow copy that a writer is notified of a freeze.

VSS first sends a Freeze event to writers initialized with VSS_APP_FRONT_END (called front-end level applications), then to writers initialized with VSS_APP_BACK_END (called back-end level applications), and finally to writers initialized with VSS_APP_SYSTEM (called system-level applications).

Syntax

typedef enum _VSS_APPLICATION_LEVEL {
  VSS_APP_UNKNOWN = 0,
  VSS_APP_SYSTEM = 1,
  VSS_APP_BACK_END = 2,
  VSS_APP_FRONT_END = 3,
  VSS_APP_SYSTEM_RM = 4,
  VSS_APP_AUTO = -1
} VSS_APPLICATION_LEVEL, *PVSS_APPLICATION_LEVEL;

Constants

 
VSS_APP_UNKNOWN
Value: 0
The level at which this writer's freeze state will occur is not known. This indicates an application
error.
VSS_APP_SYSTEM
Value: 1
This writer freeze state will occur at the system application level.
VSS_APP_BACK_END
Value: 2
This writer freeze state will occur at the back-end application level.
VSS_APP_FRONT_END
Value: 3
This writer freeze state will occur at the front-end application level.
VSS_APP_SYSTEM_RM
Value: 4
VSS_APP_AUTO
Value: -1
This writer freeze state will be determined automatically. This enumeration value is reserved for future
use.

Remarks

VSS_APPLICATION_LEVEL is provided to allow application developers to control at what point a writer will receive a Freeze event. This may be important if one writer uses or depends on another writer.

For instance, if an application X is storing data using application Y as an intermediate layer (for example, if Y implements a database used by X), we would describe X as a front-end application, and Y as a back-end application.

In this example, when freezing applications that participate in a shadow copy, you would want X (the front-end application) to suspend its writes to the database prior to freezing Y (the back-end application), the database service itself.

The application level of a writer is set by CVssWriter::Initialize and retrieved by CVssWriter::GetCurrentLevel.

Requirements

Requirement Value
Minimum supported client Windows XP [desktop apps only]
Minimum supported server Windows Server 2003 [desktop apps only]
Header vss.h

See also

CVssWriter::GetCurrentLevel

CVssWriter::Initialize