System and method for filtering write operations to a storage medium containing an operating system image

• US 7,290,115 B2
• Filed: 12/29/2004
• Issued: 10/30/2007
• Est. Priority Date: 05/21/2002
• Status: Expired due to Fees

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Beachman, Bruce J., Hill, Timothy J.
• Primary Examiner(s): Bragdon; Reginald
• Assistant Examiner(s): Namazi; Mehdi
• Application Number:
  US11/024,533
• Publication Number:
  US 20050144519A1
• Time in Patent Office: 1,035 Days
• Field of Search: None
• US Class Current: 711/207
• CPC Class Codes: G06F 11/1435 using file system or storage system metadata
• CPC Class Codes: Y10S 707/99943 Generating database or data structure, e.g. via user interface
• CPC Class Codes: Y10S 707/99953 Recoverability

Abstract

A write filter is used to handle write operations by an operating system of a computing device that has a main storage medium in which the operating system image is stored. The write filter is placed in the operating system to intercept write commands for writing state data into the main storage medium and to write the state data onto a non-volatile auxiliary storage medium to prevent the state data from being lost when the device is shut down. The write filter creates checkpoints (or watermarks) for the state data in the non-volatile memory to protect them from being written over and to allow the system to roll back to a previous state. The write filter also enables the operating system image in a writable main storage medium of the computing device to be replaced with a new operating system image while the operating system is still running through by gradually copying the new image into the main storage while moving the old image into a look-aside buffer in the RAM.

Claims

1. A computing device comprising:

a main storage medium having stored therein an operating system image, the operating image including a write filter; and

a non-volatile auxiliary storage medium,

the write filter being programmed for performing;

intercepting a write request from the operating system to write data into the main storage medium at a specified location;

writing the data of the write request and data representing the specified location into an auxiliary storage medium, the auxiliary storage medium being non-volatile;

receiving a checkpoint request to watermark data stored on the auxiliary storage medium;

creating a checkpoint for watermarking data stored in the auxiliary storage medium as of a time of the checkpoint for preventing the data stored of the time of the checkpoint from being written over;

receiving a rollback request;

in response to the rollback request, deleting data in the auxiliary storage medium stored after the checkpoint; and

removing the checkpoint to allow the data stored as of the time of the checkpoint to be written over.

2. A computing device as in claim 1, wherein the main storage medium is a read-only memory device.

3. A computing device as in claim 1, wherein the main storage medium is an optical storage device.

4. A computing device as in claim 1, wherein the auxiliary storage medium is a flash memory.

5. A computing device as in claim 1, wherein the operating system includes system file drivers and physical device drivers, and wherein the writer filter is disposed between the file drivers and physical device drivers.

6. A method of controlling write operations in a computing device having a main storage medium storing an operating system and an auxiliary storage medium, comprising:

intercepting a write request from the operating system to write data into the main storage medium at a specified location;

writing the data of the write request and data representing the specified location into an auxiliary storage medium, the auxiliary storage medium being non-volatile;

creating a checkpoint for watermarking data stored in the auxiliary storage medium as of a time of the checkpoint for preventing the data stored of the time of the checkpoint from being written over;

receiving a rollback request;

in response to the rollback request, deleting data in the auxiliary storage medium stored after the checkpoint; and

removing the checkpoint to allow the data stored as of the time of the checkpoint to be written over.

7. A method as in claim 6, wherein the main storage medium is a read-only memory device.

8. A method as in claim 6, wherein the auxiliary storage medium is a flash memory.

9. A computing device comprising:

a main storage medium having an existing operating system image stored therein; and

a look-aside buffer,

the main storage medium having stored therein a write filter programmed to replace the existing operating system in the main storage medium with a new operating system image by performing;

receiving a write request to write new data representing a portion of the new operating system image to a specific location of a virtual storage device;

checking, by the write filter, whether old data at the location in the main storage medium corresponding to the specified location of said each write request has been copied into a look-aside buffer;

if said old data has not been copied, copying said old data into the look-aside buffer; and

writing said new data into the main storage medium.

10. A computing device as in claim 9, where in the write filter is further programmed to perform:

receiving a write request directed to the main storage medium;

writing data of said write request directed to the main storage medium into the look-aside buffer;

receiving a read request directed to the main storage medium for data at a specified location;

checking whether the look-aside buffer contains buffered data corresponding the specified location of the read request; and

if the look-aside buffer contains buffered data corresponding the specified location of the read request, returning the buffered data in response to the read request.

11. A computing device as in claim 9, wherein the main storage medium is a flash memory.

12. A computing device as in claim 9, wherein the look-aside buffer is in a random access memory of the computing device.

13. A computing device as in claim 9, having computer-executable instructions for performing the step of issuing a write request to copy state data of the existing operating system image from the main storage medium to the virtual storage device.

14. A method of replacing an old software program image in a main storage medium of a computing device with a new software program image, comprising:

turning on a write filter in an operating system of the computing device;

issuing write requests to progressively copy portions of the new software program image into a virtual storage device;

receiving, by the write filter, a write request to write new data to a specific location of the virtual storage device;

checking, by the write filter, whether old data at the location in the main storage medium corresponding to the specified location of said each write request has been copied into a look-aside buffer;

if said old data has not been copied, copying said old data into the look-aside buffer; and

writing said new data into the main storage medium.

15. A method as in claim 14, wherein the old and new software program images are operating system images.

16. A method as in claim 14, further comprising steps performed by the write filter:

receiving a write request directed to the main storage medium;

writing data of said write request directed to the main storage medium into the look-aside buffer;

receiving a read request directed to the main storage medium for data at a specified location;

checking whether the look-aside buffer contains buffered data corresponding the specified location of the read request; and

if the look-aside buffer contains buffered data corresponding the specified location of the read request, returning the buffered data in response to the read request.

17. A method as in claim 14, wherein the main storage medium is a flash memory.