PROVIDING MULTIPLE CONCURRENT ACCESS TO A FILE SYSTEM

• US 20110055274A1
• Filed: 11/04/2010
• Published: 03/03/2011
• Est. Priority Date: 02/06/2004
• Status: Active Grant

• Current Assignee: Vmware LLC (Broadcom, Inc.)
• Original Assignee: VMware, Inc. (Broadcom, Inc.)
• Inventors: SCALES, Daniel J., VAGHANI, Satyam B.
• Granted Patent: US 8,489,636 B2
• Time in Patent Office: Days
• US Class Current: 707/781
• CPC Class Codes: G06F 16/10 File systems; File servers
• CPC Class Codes: G06F 16/2343 Locking methods, e.g. distributed locking or locking implementation details
• CPC Class Codes: G06F 21/6218 to a system of files or objects, e.g. local or distributed file system or database

Abstract

Multiple computers are connected to a data storage unit that includes a file system, which further includes multiple data entities, including files, directories and the file system itself. The file system also includes, for each data entity, an owner field for indicating which computer, if any, has exclusive or shared access to the data entity, along with a time field for indicating when a lease of the data entity began. When a computer wants to lease a data entity, the computer uses a disk reservation capability to temporarily lock the data storage unit, and, if the data entity is not currently leased, the computer writes its own identification value into the owner field and a current time into the time field for the data entity, to claim the data entity for a renewable lease period. If a prior lease of a data entity has expired, another computer may break the lease and claim ownership for itself.

Claims

1. A computer system providing concurrent access to data stored in accordance with a file system, the computer system comprising:

a plurality of computers, wherein each of the computers accesses data in accordance with the file system;

a data storage unit networked to each of the plurality of computers and storing data in accordance with the file system, wherein the file system enables a file stored in the data storage unit to be accessible by each of the plurality of computers, without utilizing another computing entity acting on its behalf, by associating an owner field and a time field with the file, the owner field used to determine whether one of the plurality of computers currently has exclusive access to the file and the time field used to determine whether a time period for exclusive access to the file has expired.

2. The computer system of claim 1, wherein the owner field and the time field are included in a lock corresponding to the file.

3. The computer system of claim 1, wherein the lock further comprises an access field indicating whether the file is available for read-access by multiple computers.

4. The computer system of claim 3, wherein the lock further comprises a count field indicating a number of computers currently possessing read-only access to the file.

5. The computer system of claim 3, wherein the lock further comprises one or more additional owner fields and corresponding time fields to indicate computers having read-only access to the file.

6. The computer system of claim 1, wherein at least one of the computers is a virtual machine running on a server configured to support multiple virtual machines.

7. The computer system of claim 3, wherein the owner field is configured to store a unique identifier of the virtual machine when the virtual machine has acquired exclusive access to the file.

8. The computer system of claim 3, wherein the file comprises contents of a virtual disk corresponding to the virtual machine.

9. The computer system of claim 1, wherein at least one of the computers is a server supporting the running of virtual machines.

10. The computer system of claim 1, wherein the file is further associated with a queue comprising one or more additional owner fields and corresponding time fields to indicate other computers that are waiting to access the file.

11. A non-transient computer readable storage medium comprising instructions that are to be executed in a computer for accessing a file in a file system configured to provide concurrent access to the data stored in accordance with the file system, wherein the computer is one of a plurality of computers networked to a data storage unit storing data in accordance with the file system and wherein the instructions cause the computer to carry out the steps of:

reading an owner field stored in the file system and associated with the file;

if the owner field indicates that no other computer currently has exclusive access to the file, writing a unique identifier of the computer into the owner field and a time value into a corresponding time field thereby acquiring exclusive access to the file for a period of time indicated by the time value;

if the owner field indicates that another computer has exclusive access to the file, reading the corresponding time field and, if the corresponding time field indicates that a time period has lapsed, writing the unique value into the ownership field and the time value into the corresponding time field thereby acquiring exclusive access to the file for a period of time indicated by the time value, else if the corresponding time field indicates a time period has not lapsed, delaying access to the file; and

if exclusive access to the file has been acquired, accessing the file.

12. The non-transient computer readable storage medium of claim 11, wherein the owner field and the corresponding time field are included in a lock corresponding to the file.

13. The non-transient computer readable storage medium of claim 11, wherein the lock further comprises an access field indicating whether the file is available for read-access by multiple computers.

14. The non-transient computer readable storage medium of claim 13, wherein the lock further comprises a count field indicating a number of computers currently possessing read-only access to the file.

15. The non-transient computer readable storage medium of claim 11, wherein the computers is a virtual machine running on a server configured to support multiple virtual machines.

16. A method for accessing a file in a file system configured to provide concurrent access to data stored in accordance with the file system, the method performed in a computer, without utilizing another computing entity acting on its behalf, networked to a data storage unit storing data in accordance with the file system and comprising:

reading an owner field stored in the file system and associated with the file;

if the owner field indicates that no other computer currently has exclusive access to the file, writing a unique identifier of the computer into the owner field and a time value into a corresponding time field thereby acquiring exclusive access to the file for a period of time indicated by the time value;

if the owner field indicates that another computer has exclusive access to the file, reading the corresponding time field and, if the corresponding time field indicates that a time period has lapsed, writing the unique value into the ownership field and the time value into the corresponding time field thereby acquiring exclusive access to the file for a period of time indicated by the time value, else if the corresponding time field indicates a time period has not lapsed, delaying access to the file; and

if exclusive access to the file has been acquired, accessing the file.

17. The method of claim 16, wherein the owner field and the corresponding time field are included in a lock corresponding to the file.

18. The method of claim 16, wherein the lock further comprises an access field indicating whether the file is available for read-access by multiple computers.

19. The method of claim 18, wherein the lock further comprises a count field indicating a number of computers currently possessing read-only access to the file.

20. The method of claim 16, wherein the computers is a virtual machine running on a server configured to support multiple virtual machines.