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

• US 6,907,512 B2
• Filed: 05/21/2002
• Issued: 06/14/2005
• Est. Priority Date: 05/21/2002
• Status: Active Grant

• Current Assignee: Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Microsoft Corporation
• Inventors: Beachman, Bruce J., Hill, Timothy J.
• Primary Examiner(s): Padmanabhan, Mano
• Assistant Examiner(s): Namazi, Mehdi
• Application Number:
  US10/152,262
• Publication Number:
  US 20030221083A1
• Time in Patent Office: 1,120 Days
• Field of Search: 711/207, 711/154, 711/156, 711/161, 714/6, 707/202, 707/203, 719/328, 719/329
• 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 computer-readable medium having computer-executable instructions for performing steps by a write filter in an operating system running in a computing device, the computer having a main storage medium having stored thereon an operating system image, the steps 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;

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 computer-readable medium having computer-executable instructions for replacing an old operating system image in a computing device with a new operating system image, the old operating system image residing in a main storage medium of the computing device, the steps comprising:

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

issuing write requests to progressively copy portions of the new operating system 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.

3. A computer-readable medium as in claim 2, further computer-executable instructions for the write filter to perform the steps of:

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.

4. A computer-readable medium as in claim 2, wherein the main storage medium is a flash memory.

5. A computer-readable medium as in claim 2, wherein the look-aside buffer is in a random access memory of the computing device.

6. A computer-readable medium as in claim 2, having further computer-executable instructions for performing the step of issuing a write request to copy state data of the operating system from the main storage medium to the virtual storage device.

7. A method for replacing an old operating system image in a computing device with a new operating system image while the computing device is in operation, the old operating system image residing in a main storage medium of the computing device, comprising the steps of:

turning on a write filter component in an operating system of the computing device, the write filter being disposed in the operating system to intercept write requests and being programmed to perform the steps of;

checking, upon receiving a write request to write new data to a virtual storage device at a specified location, whether old data in the main storage medium corresponding to the specified location of said write request has been copied into a look-aside buffer;

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

writing said new data into the main storage medium, and

issuing write requests to copy portions of the new operating system image into the virtual storage device.

8. A method as in claim 7, further including the steps of requesting a name for the virtual storage device from the write filter;

and receiving the name of the virtual storage device for use in the write requests to copy portions of the new operating system image.

9. A method as in claim 7, wherein the main storage medium is a flash memory.

10. A method as in claim 7, further including the step issuing a write request to copy state data of the operating system from the main storage medium to the virtual storage device.

11. A computer-readable medium having computer-executable instructions for replacing an old software program image in a computing device with a new software program image, the old software program image residing in a main storage medium of the computing device, the steps 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.

12. A computer-readable medium as in claim 11, wherein the old and new software program images are operating system images.

13. A computer-readable medium as in claim 11, having further computer-executable instructions for the write filter to perform the steps of:

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.

14. A computer-readable medium as in claim 13, wherein the main storage medium is a flash memory.