File based volumes and file systems
A file-mapped volume is a logical volume in which the data storage of the logical volume is the data storage of a regular file associated with the logical volume. The regular file can be a file of a first file system, and a second file system can be built upon the file-mapped volume. These two file systems can have distinct inode address spaces, yet files of the first file system are easily moved to the second file system by changing pointers to inodes of these files. The second file system can be easily copied, attached, or transported by copying, attaching, or transporting the regular file containing the second file system, yet files in the second file system can be accessed in real time via file access routines of the operating system.
1. A computer-implemented method of operating a data processing apparatus, said method comprising:
configuring a logical volume of computer data storage so that the logical volume is mapped to storage of an associated file of the computer data storage and the logical volume is contained in the associated file;
a file system manager of an operating system of the data processing apparatus creating and maintaining a file system on the logical volume; and
the file system manager accessing the associated file in response to a file access request from a user or application program for access to the file system;
which includes the file system manager producing a volume I/O request for access to the logical volume in response to the file access request from the user or application program, and the operating system converting the volume I/O request to a file I/O request to access the associated file and returning the file I/O request to the file system manager; and
wherein the configuring of the logical volume of computer data storage so that the logical volume is mapped to storage of the associated file of the computer data storage and the logical volume is contained in the associated file includes setting a file-mapped logical volume type attribute of the logical volume and setting an associated file name attribute of the logical volume to specify that the associated file is the associated file for containing the logical volume; and
the operating system converting the volume I/O request to a file I/O request to access the associated file includes the operating system producing the file I/O request to access the associated file in response to finding that the logical volume has the file-mapped logical volume type attribute and an associated file name attribute specifying the associated file.
2. The computer-implemented method as claimed in claim 1 , wherein the operating system returns the file I/O request to the file system manager by sending a recursive call to the file system manager for reading or writing to the associated file.
3. The computer-implemented method as claimed in claim 1 , wherein the file system manager has support for sparse files, the logical volume has more logical blocks than the number of physical blocks allocated to the logical volume, the associated file is a sparse file supported by the file system manager, and the file system manager allocates physical blocks to the logical volume as data are written to the logical volume.
4. The computer-implemented method as claimed in claim 1 , wherein the configuring of the logical volume of computer data storage so that the logical volume is mapped to storage of the associated file of the computer data storage and the logical volume is contained in the associated file further includes setting an associated file type attribute of the associated file and setting a volume name attribute of the associated file to specify that the logical volume is the file-mapped logical volume that uses the storage of the associated file.
5. A data processing apparatus comprising:
computer data storage; and
at least one data processor coupled to the computer data storage for access to data stored in the computer data storage;
wherein said at least one data processor is programmed with an operating system defining a file-mapped volume type in which a logical volume of the computer data storage is mapped to storage of an associated file of the computer data storage and the logical volume is contained in the associated file; and
said at least one data processor is programmed to configure the logical volume of computer data storage so that the logical volume is mapped to storage of the associated file of the computer data storage by setting a file-made logical volume type attribute of the logical volume and setting an associated file name attribute of the logical volume to specify that the associated file is the associated file for containing the logical volume; and
wherein the operating system is programmed with a file system manager for maintaining file systems on logical volumes of the computer data storage, and the operating system is programmed for using the file system manager for maintaining a file system on a file-mapped volume; and
the operating system is programmed with a file mapped volume interface that, when executed by said at least one data processor, receives a volume I/O request from the file system manager for access to the logical volume and converts the volume I/O request to a file I/O request to access the associated file by producing the file I/O request to access the associated file in response to finding that the logical volume has the file-mapped logical volume type attribute and an associated file name attribute specifying the associated file, and returns the file I/O request to the file system manager.
6. The data processing apparatus as claimed in claim 5 , wherein the file mapped volume interface returns the file I/O request to the file system manager by sending a recursive call to the file system manager for reading or writing to the associated file.
7. The data processing apparatus as claimed in claim 5 , wherein the operating system includes a volume layer for responding to volume I/O requests for access to the computer data storage of the logical volumes, a file system program layer including the file system manager for processing file access requests from users or applications, and a file-mapped volume interface layer between the file system layer and the volume layer, the file-mapped volume interface layer including the file-mapped volume interface and being programmed to receive volume I/O requests from the file system layer for access to specified logical volumes, and
when a volume I/O request from the file system layer is not a request for access to a specified file-mapped volume, to pass the volume I/O request from the file system layer to the volume layer.
8. The data processing apparatus as claimed in claim 5 , wherein the file system manager has support for sparse files, the logical volume has more logical blocks than the number of physical blocks allocated to the logical volume, the associated file is a sparse file supported by the file system manager, and when executed by said at least one data processor, the file system manager allocates physical blocks to the logical volume as data are written to the logical volume.
9. The data processing apparatus as claimed in claim 5 , wherein said at least one data processor is further programmed to configure the logical volume of computer data storage so that the logical volume is mapped to storage of the associated file of the computer data by setting an associated file type attribute of the associated file and setting a volume name attribute of the associated file to specify that the logical volume is the file-mapped logical volume that uses the storage of the associated file.