Virtual deletion in merged file system directories

• US 7,756,821 B2
• Filed: 11/02/2006
• Issued: 07/13/2010
• Est. Priority Date: 11/02/2006
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Khalidi, Yousef A., Talluri, Madhusudhan, Smith, Frederick J., Havens, Jeffrey L.
• Primary Examiner(s): Vo; Tim T.
• Assistant Examiner(s): Mobin; Hasanul
• Application Number:
  US11/555,745
• Publication Number:
  US 20080109394A1
• Time in Patent Office: 1,349 Days
• Field of Search: None
• US Class Current: 707/600
• CPC Class Codes: G06F 16/162 Delete operations erasing in storage systems G06F3/0652
• CPC Class Codes: G06F 16/235 Update request formulation

Abstract

An element of a file system is virtually deleted by creating a deletion marker for the element. Two or more separate physical file system directories are presented as one merged (virtual) file system directory to a process running in a silo. The operating system provides the merged view of the file system directories by monitoring file system requests made by processes in silos on a computer or computer system and filtering out those elements associated with deletion markers. Special processing is invoked in response to detecting certain types of file system access requests, including: enumeration, open, create, rename or delete.

Claims

1. A system for performing a virtual deletion of an element in a merged directory comprising:

a processor;

a memory coupled to said processor;

at least a portion of an operating system stored on said memory and configured to execute program code containing instructions that when executed by the processor;

divide processing space into a plurality of execution environments (silos);

provide a merged view of a plurality of file system directories comprising a private directory and at least one public directory for processes running in each of the plurality of silos, wherein each silo has a merged view that is specific to that silo, wherein access to the plurality of file system directories by the processes is based on the silo in which the processes are placed, wherein the program code causes the operating system to create the merged view specific to the silo by monitoring file system access requests initiating from the processes running in the silo and in response to detecting a file system deletion request, performs callback processing that creates a deletion marker for an element identified in the file system deletion request, wherein the element for which the deletion marker has been created is filtered from the merged view of the plurality of the file system directories that appears to the processes running in the silo as a single directory comprising entries in the plurality of file system directories, and wherein virtual deletion of the element identified in the deletion request in the private directory hides a same-named element in the at least one public directory.

2. The system of claim 1, wherein each of the plurality of file system directories is associated with a rank.

3. The system of claim 2, wherein the rank associated with each of the plurality of file system directories is used as a tiebreaker to determine entries included in the silo-specific view when more than one entry in the plurality of directories is known by a particular name.

4. The system of claim 1, wherein the operating system includes a filter driver that detects virtual deletions via callbacks inserted in file system access request processing paths comprising delete processing, enumeration processing, create processing, open processing and rename processing.

5. The system of claim 4, wherein the file system deletion request creates a deletion marker for the file system element identified in the file system deletion request.

6. A method for providing a view of a plurality of file system directories comprising a view of a virtual merged directory comprising a plurality of file system directories comprising a private directory and at least one public directory to processes running in a one of a plurality of execution environments contained within a single operating system environment (silo) comprising:

monitoring access requests made by processes running in the silo using a filter driver in an operating system, wherein access to the plurality of file system directories by the processes is based on the silo in which the processes are placed, wherein the filter driver detects virtual deletion of an element of a file system by presence of a deletion marker associated with the element;

in response to detecting the deletion marker, performing processing associated with a type of file access request wherein the element associated with the deletion marker is filtered from the view of the plurality of file system directories and hiding a same-named element as the element identified in the deletion request in the at least one public directory.

7. The method of claim 6, further comprising creating the deletion marker by decorating an identifier of the element with text indicating virtual deletion.

8. The method of claim 6, further comprising storing the deletion marker in an external file.

9. The method of claim 6, wherein in response to determining that the file access request is an enumerate file or enumerate directory operation, the operating system returns the view wherein the view comprises a list of entries in the first file directory and the second file directory except for entries associated with deletion markers.

10. The method of claim 6, wherein in response to determining that the file access request is an enumerate file or enumerate directory operation, the operating system returns the view wherein the view comprises a list of entries in the first file directory and the second file directory except for entries comprising deletion markers.

11. The method of claim 6, wherein a file access request that renames a file system element to a name indicating virtual deletion is prohibited.

12. The method of claim 6, wherein a file access request that attempts to open an element associated with a deletion marker fails.

13. The method of claim 6, wherein access of the process to entries in the second file directory is read-write access.

20. The method of claim 6, wherein access of the process to entries in the first file directory is restricted to read-only access via creation of the view.

14. A computer-readable storage medium having program code stored thereon that, when executed by a computing environment, causes the computing environment to:

use a filter driver of an operating system to monitor processes running in one of a plurality of execution environments contained within a single operating system environment (silo), wherein the filter driver detects a file access request made by a process running in the silo;

in response to detecting the file access request, perform processing associated with a type of file access request wherein a view of a plurality of physical file directories is provided to the process, wherein the view presents the plurality of physical file directories comprising a private directory and at least one public directory to the process as a single merged virtual directory comprising entries of the plurality of physical file directories, wherein entries associated with deletion markers are eliminated from the view, wherein access to the plurality of physical file directories by the processes is based on the silo in which the processes are placed and hiding a same-named element as the element identified in the deletion request in the at least one public directory.

15. The computer-readable storage medium of claim 14, having further program code stored thereon, that when executed by the computing environment, causes the computing environment to:

associate a deletion marker with an element identified by a delete access request, wherein the deletion marker comprises a decorated element identifier.

16. The computer-readable storage medium of claim 14, having further program code stored thereon, that when executed by the computing environment, causes the computing environment to:

associate a deletion marker with an element identified by a delete access request, wherein the deletion marker is stored in an external datastore.

17. The computer-readable storage medium of claim 14, having further program code stored thereon, that when executed by the computing environment, causes the computing environment to:

associate a deletion marker with an element identified by a delete access request, wherein the deletion marker is stored in the file system.

18. The computer-readable storage medium of claim 15, having further program code stored thereon, that when executed by the computing environment, causes the computing environment to:

filter out elements associated with deletion markers when an enumerate request is received.

19. The computer-readable storage medium of claim 15, having further program code stored thereon, that when executed by the computing environment, causes the computing environment to:

prohibit renaming an element to a name indicating that the element has been deleted.