VMware vSphere SDKs and Tools 6.7

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Access Files on Virtual Disks

It might be necessary for a backup application to access individual files or groups of files on the virtual disks. For example, data protection applications might need to restore individual files on demand.
You can find the interfaces to accomplish this in the
VixMntapi
 library associated with
VixDiskLib
. The
VixMntapi
 library allows disks or volumes of a virtual machine to be mounted and examined as needed.
VixMntapi
 provides access at the file system level, whereas
VixDiskLib
 provides access at the sector level.
To mount a virtual disk
  1. Locate the path names of all the virtual disks associated with a snapshot.
  2. Call
    VixDiskLib_Open()
     to open all of these virtual disks. This gives you a number of
    VixDiskLib
     handles, which you should store in an array.
  3. Call
    VixMntapi_OpenDiskSet()
     to create a
    VixDiskSetHandle
    , passing in the array of
    VixDiskLib
     handles that you created in step 2.
  4. Pass
    VixDiskSetHandle
     as a parameter to
    VixMntapi_GetVolumeHandles()
     to obtain an array of
    VixVolumeHandle
     pointers to all volumes in the disk set.
  5. Call
    VixMntapi_GetOsInfo()
     to determine what kind of operating system is involved, and decide where important pieces of information are to be found.
  6. For important volumes, call
    VixMntapi_MountVolume()
     then
    VixMntapi_GetVolumeInfo()
    , which reveals how the volume is set up. (Unimportant volumes include swap partitions.)
  7. If you need information about how the guest operating system sees the data on this volume, you can look in the data structure
    VixVolumeInfo
     returned by
    VixMntapi_GetVolumeInfo()
    . For example,
    VixVolumeInfo::symbolicLink
    , obtained using
    VixMntapi_GetVolumeInfo()
    , is the path on the proxy where you can access the virtual disk’s file system using ordinary open, read, and write calls.
Once you are done accessing files in a mounted volume, there are
VixMntapi
 procedures for taking down the abstraction that you created. These calls are:
  • VixMntapi_DismountVolume()
     for each volume handle
  • VixMntapi_FreeOsInfo()
     and
    VixMntapi_FreeVolumeInfo()
  • VixMntapi_CloseDiskSet()
This leaves the
VixDiskLib
 handles that you obtained in the beginning; you must dispose of them properly.

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