Abstract:
A file system independent virtualized boot block with discovery volume and cover files renders a volume visible when accessed by an accessing system which differs from a source system. For example, a downlevel operating system recognizes that data is present on a volume created in an uplevel operating system, even where the uplevel data itself may not be accessible.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation application which claims priority to commonly assigned, co-pending U.S. patent application Ser. No. 12/257,938, filed Oct. 24, 2008, which application is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Access to data across multiple file systems is a significant concern for computer users. Users may encounter difficulties when trying to access file systems supported in a source system but not supported in an accessing system. For example, a source file system may incorporate features such as encryption or compression which are not recognizable by an accessing device using a different file system. 
     Attempts to access volumes containing a file system incompatible with the accessing device may have unintended consequences for users. The accessing system may not recognize the file system of the source system and present the volume as “raw.” At the least, the accessing system may not be able to determine that data is present on that volume. At worst, an accessing system which fails to recognize the volume may prompt the user to reformat the entire volume, causing loss of the data in the volume. 
     SUMMARY 
     An original boot block (or boot sector) of a volume on a computer readable storage medium and the blocks following it are moved to another location on the volume and a discovery volume is initialized and takes their place. The discovery volume comprises a file system recognizable by a desired array of accessing devices with one or more pointers in its boot block to metadata which leads to the blocks that were relocated to accommodate the discovery volume at the beginning of the volume, and acts as an overlay for the primary file system. For example, a discovery volume using a File Allocation Table (FAT) format contains boot block entries consistent with a FAT boot block, and one or more pointers to metadata which leads to the relocated boot blocks of the primary file system on the volume. 
     The discovery volume may contain an information file for users alerting them to the presence of data on the volume. The discovery volume may also store driver or access software necessary for reading the primary file system on the volume. Use of an overlay comprising a commonly recognized format, for example a FAT volume, renders the primary file system on the volume independent of a source system. 
     Thus, when attempting to mount a disk containing a primary file system unrecognized by the accessing system, the accessing system will surface the discovery volume to the user. Based on the information presented in that discovery volume, a user may ascertain that an encrypted file system is present. Additionally, the presence of the discovery volume prevents a prompt to reformat the volume. 
     Data in the primary file system may be further accessed or protected using cover files. Cover files make it appear to the accessing system as though the discovery volume claims space actually used by the primary file system. Thus, while a discovery volume may actually utilize a small number of sectors on the disk, an accessing system may see the discovery volume consuming the entire space. 
     Virtualization of the blocks where the discovery volume resides (or boot blocks) may take place at multiple levels in the operating system concurrently. 
     This summary introduces the subject matter of virtualized bootblocks, described below in the Detailed Description. This summary is not intended to identify essential features of the claimed subject matter, nor is it intended for use in determining the scope of the claimed subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure is made with reference to the accompanying figures. In the figures, the left most reference number digit identifies the figure in which the reference number first appears. The use of the same reference numbers in different figures indicates similar or identical terms. 
         FIG. 1  is a diagram of an exemplary computer system. 
         FIG. 2  is a diagram of an exemplary boot block of a discovery volume wherein the discovery volume is a FAT volume. 
         FIG. 3  is a diagram of the locations of objects by sector on a physical disk. 
         FIG. 4  is a flow diagram showing the initialization of a discovery volume. 
         FIG. 5  is a flow diagram showing the use of the discovery volume boot block. 
         FIG. 6  is a diagram of the locations of cover files to render the drive apparently full to an operating system which cannot read the primary file system. 
         FIG. 7  illustrates one exemplary implementation of how the virtualization of the boot blocks may occur concurrently at different levels in the operating system. 
     
    
    
     DETAILED DESCRIPTION 
     Initialization and use of a discovery volume are described in this specification. The data at the beginning of a volume of a computer readable storage medium is first moved to another location. A discovery volume is then written to the recently vacated space. The discovery volume boot block contains entries consistent with a file system boot block, and pointers to metadata which leads to the relocated blocks. The discovery volume may contain one or more information files describing the underlying primary file system. The information files may be visible to users and contain data which is human readable, machine readable, or both, as to the nature of the other volumes on the disk. The access software may provide for drivers, translation, decompression, decryption, etc., necessary to provide the accessing systems with the ability to read the contents of the primary volume. 
     In one implementation, FAT may be used. Because of the FAT format&#39;s wide support, the discovery volume would be visible across a wide range of platforms and operating systems. However, any file system may be utilized which provides the desired commonality across accessing systems. 
     For example, because of this commonality across accessing systems, when attempting a mount of a physical disk containing an encrypted volume by an accessing system which lacks the drivers necessary to read the encrypted data, the accessing system will still find the discovery volume accessible. Based on the information presented in that discovery volume, a user may ascertain that an encrypted volume is present. Additionally, the presence of the discovery volume prevents a prompt to reformat the volume. 
     Virtualization of the boot blocks may take place at one or more levels in the operating system concurrently, including at the Full Volume Encryption (FVE), write aggregator, and file system levels. 
     Data in the primary volume may be further protected using cover files. Cover files make it appear to the accessing system as though the discovery volume claims space actually used by the primary file system. Thus, while a discovery volume may actually utilize a small number of sectors on the disk, an accessing system may see the discovery volume consuming the entire space. Cover files may also be used to provide access to the underlying volume. 
       FIG. 1  is a diagram of an exemplary computer system  100  which may incorporate various elements including a processor, computer readable storage media such as magnetic disks, optical disks, flash memory, random access memory (RAM), and the like. 
     An operating system  102  may be executed on computer system  100 . 
     At  104 , is a file system within operating system  102 . 
     At  106 , a volume filter driver may be employed. For example, the writelog.sys filter driver may be employed to perform write aggregation. 
     At  108 , another volume filter driver may be employed. For example, the fvevol.sys filter driver may be employed to enable support of full volume encryption (FVE) including Microsoft® BitLocker™ drive encryption (BDE) made by Microsoft® of Redmond, Wash. 
     At  110 , a volume manager such as volmgr.sys is employed to manage volumes stored on physical disks  112 . 
     At  112 , the physical disk or disks which contain the volumes managed by volume manager  110  are shown. “Disks” as used herein includes magnetic and optical disks, as well as any computer readable storage medium including optical media, magnetic media, barcodes, holographic storage, solid state memory, and the like. 
     A discovery volume  114  is shown on the physical disk  112  within primary volume  118 . Within discovery volume  114  is a boot block  116 . The discovery volume may utilize any of the desired file system implementations, including FAT12, FAT16, FAT32, exFAT, FATX, UDF, NTFS, ext2, ext4, Joliet extension to the ISO 9660 file system (“compact disk file system”), Tux3, etc. Other implementations may use other types of file systems as well. 
     Also within primary volume  118  is primary file system metadata  120 . The primary volume may utilize any of the file systems describe above, in addition to compression, encryption, and other functions. For example, a primary volume may use full volume encryption (FVE) using BitLocker™ and a fvevol.sys filter driver. 
     The discovery volume may be configured to hold a selected set of files under the root directory or an equivalent data structure. These files may include the information file and accessing software discussed previously. Enforcing a read-only mount would also protect the discovery volume. 
     At  118 , a full volume encryption (FVE) volume  118  resulting from use of BitLocker™ and the fvevol.sys filter driver is shown. 
       FIG. 2  is a diagram of an exemplary discovery volume  114  containing a virtualized boot block  116 . Within the virtualized boot block  116  a BIOS parameter block may be  202  present. Also within the virtualized boot block  116  of discovery volume  114  is a pointer  210  to a metadata location  120 . This pointer  210  to metadata  120  refers to the primary volume metadata  120  located within the primary volume  118 . Also within the discovery volume is discovery volume file structure  204 . 
     At  206 , an information file may also be present within the discovery volume  114 . This information file may be visible to users and contain human readable, machine readable, or both, information as to the nature of the other volumes on the disk. This information file may be stored in plain text, or hypertext markup language (HTML), or other suitable file format. The information file may contain a warning to users that the volume contains encrypted data, and refer them to a specific Internet address for technical support. 
     At  208 , access software within discovery volume may be stored. The access software may provide for drivers, translation, decompression, decryption, and the like to provide accessing systems with the ability to read the contents of the primary file system on the volume. 
     Also within primary volume  118  are the relocated boot blocks of the primary file system  212  and data  214 . Pointer to metadata  210  may also point directly to relocated boot blocks of the primary file system  212  where the component utilizing the discovery volume does not utilize metadata. 
     For example, where the discovery volume file structure uses a FAT format, within the boot block  116  additional information such as a complete BIOS parameter block (BPB) and associated fields may be present. Because some portions of the boot block are not critical for FAT functionality other data may be stored therein including pointers to the metadata of the component utilizing the discovery volume, such as the fvevol.sys filter driver. As a result, these fields may be used to store information necessary for the FVE volume to function while still leaving a functional FAT discovery volume. 
     Within the book block  116  using a FAT format, the OEM field (0x03) may be used. For convenience, the addresses for boot block fields are given as a hexadecimal number relating to their boot block locations. These offsets are given for illustrative purposes, and other offsets are possible, depending upon implementation. 
     When BitLocker™ is implemented in a volume, the boot block OEM string contains the value of “-FVE-FS-” which is used (for example, by Microsoft® Windows Vista®) to identify that the volume is encrypted. 
     When the FAT structure is in use, the boot block contains fields representing the FAT file structure within the discovery volume. 
     A RootDirectory (or RootEntry) field (0x11) may also be present in the virtualized boot block  116  when the FAT file structure is in use. The RootDirectory field is used to determine placement of files used for end-user information, such as a “readme.txt” file or access software. 
     When the FAT file structure is used by the discovery volume, the VolumeLabel field (0x2b) may be updated to contain “BitLocker,” “BDE Volume” or a similar string useful to identify that an encrypted volume is present. 
       FIG. 3  is a diagram of the locations  300  of objects by sector on the physical disk  112 . The actual locations and relative positions of objects in a volume may vary. 
     At  114  the discovery volume is shown with boot block  116  within. Within that boot block  116  a pointer  210  points to the metadata  120 . 
     The metadata  120  contains a pointer  302  to the relocated real or original boot blocks  212 . When the primary volume  118  uses FVE, the metadata used by BitLocker™ is generally unencrypted, although portions may be encrypted. When BitLocker™ is used, three identical copies of the metadata are stored throughout the volume for backup purposes. Because the BitLocker™ metadata locations  120  are similar to one another (for example, pointer locations to the other metadata locations may change), each will also contain a pointer  302  to the relocated boot blocks  212 . For clarity, these pointers are not illustrated in  FIG. 3 . Also, a BitLocker™ metadata location may contain references  304  to other BitLocker™ metadata locations. 
       FIG. 4  is a flow diagram showing the initialization of a discovery volume  400 . 
     At  402 , a discovery volume is initialized in memory. 
     At  404 , a boot block is initialized within the discovery volume. For example, where FVE is used, this may be done during initialization of the BitLocker™ Drive Encryption (“BDE”). 
     At  406 , the original real boot block and the blocks following it are moved to a new location in the volume. This location may be encrypted or unencrypted. Alternately, the real boot blocks may be stored in the metadata. 
     At  408 , a pointer is constructed in the new boot block which points to a data structure containing information referring to a real (or original) boot blocks. For example, the pointer may refer to a BitLocker™ metadata file location which in turn refers to an encrypted real boot blocks. 
     At  410 , the discovery volume is written out to the beginning of the volume. 
       FIG. 5  is a flow diagram showing the use  500  of the boot block. At  502 , a boot block is read by the file system. 
     At  504 , when the driver or other software utilizing the discovery volume is present, at  506  the pointer in the boot block to metadata is followed. The metadata in  506  then refers to the real boot block, which at  508  is used to satisfy the read of the boot block by the file system. Thus, by redirecting the reads and writes for the blocks that the discovery volume occupies to the location where the real boot blocks were moved, the discovery volume becomes invisible (virtualized) and the primary file system is able to mount. 
     Returning to  504 , when the driver or other software utilizing the discovery volume is not present, at  510  the discovery volume is presented to the user and the discovery boot block read. The primary file system remains inaccessible. 
       FIG. 6  is a diagram of cover files rendering a volume apparently full to an operating system which cannot read the primary file system. 
       602  depicts the volume of  FIG. 3 . For example, assume the volume of  FIG. 3  is a primary volume comprising a BitLocker™ encrypted volume when accessed from a BitLocker™ capable operating system. The primary file system is recognized, and the data and metadata are visible and available for access. 
       604  depicts the volume of  602  when the primary file system is not recognized. This may occur, for example, if the Bitlocker™ encrypted volume is accessed using a computer with the Windows 98® operating system. In that case, the discovery volume  114  would be accessible, as well as the boot block  116 . However, the remainder of the volume would be unreadable by Windows98® and therefore appear as apparently unallocated space  606 . This unallocated space  606  may thus be erroneously viewed by the operating system as being available for reformatting or operations which could destroy the encrypted data  314  and metadata  304  which is actually present. 
       608  depicts the volume of  604  when cover file  610 (A)-(N) entries are present in the discovery volume  114 . For example, where the discovery volume uses a FAT format, cover files  610  exist as entries within the FAT file allocation table discovery volume  114 . Cover files  610  appear to claim the space that would otherwise appear to the operating system as unallocated space  606 . One implementation minimizes the count of cover files  610  by making as many of the cover file entries in the discovery volume as possible appear to be the maximum file size permitted by discovery volume file structure, with one cover file sized to fill any remainder of the volume. For example, if a drive is 18 gigabytes (GB), and the discovery volume file structure had a maximum file size of four GB, then four 4 GB cover files and one 2 GB cover file would appear to be on the volume. 
     The cover files  610  may also have attributes configured as permitted within the implementation of discovery volume file system used. For example, the cover files  610  may have read-only and system file attributes set. 
       FIG. 7  illustrates how the virtualization of the boot blocks may occur concurrently at different levels in an operating system  700 . By implementing the virtualization of the boot blocks as a filter driver at a given level, operations at levels above and below are unaffected. Thus, the volume may be virtualized at multiple levels concurrently. 
     At  702 , the volume as presented to the file system driver is shown. At  704 , the file system boot blocks within the volume of the file system driver are shown at the beginning of the virtualized volume. 
     At  714 , a virtualized volume shown from the perspective of a write aggregator driver is shown. At  716 , within this virtualized volume is the relocated file system boot blocks. Because the boot blocks have been virtualized at this layer, they do not need to be present at the beginning of the volume, and may be within the portion of the volume normally used for data. At  718 , the write aggregator boot blocks are shown. 
     At  720 , a virtualized volume from the perspective of the Bitlocker™ full volume encryption (FVE) perspective is shown. At  722 , within this virtualized volume is the relocated write aggregator boot blocks. Because the boot block has been virtualized at this layer, the boot block does not need to be present at the beginning of the volume. At  724 , the Bitlocker™ boot blocks are shown. This volume  720  is synonymous with volume  118  shown in  FIG. 1 . 
     The virtualization and offsets shown above prevent the boot block of one level from colliding with the boot block virtualized on another. 
     FVE may be enabled on any operating system by performing the following steps:
         1) FVE creates and pins the metadata files.   2) FVE creates and pins the boot blocks file.   3) FVE queues all reads/writes to the volume.   4) FVE reads the boot blocks by sending a read input/output request packet to the volume manager directly.   5) FVE backs up the boot blocks read from the volume manager.   6) FVE writes its metadata to the volume.   7) FVE writes the discovery volume to the volume.   8) FVE resumes all queued reads/writes to the volume.       

     CONCLUSION 
     Although specific details of exemplary methods are described with regard to the figures and other flow diagrams presented herein, it should be understood that certain acts shown in the figures need not be performed in the order described, and may be modified, and/or may be omitted entirely, depending on the circumstances. Moreover, the acts described may be implemented by a computer, processor or other computing device based on instructions stored on one or more computer-readable storage media. The computer-readable storage media can be any available media that can be accessed by a computing device to implement the instructions stored thereon.