Working with Virtual Disk Data

The virtual disk library reads and writes sectors of data. It has no interface for character or byte-oriented I/O.

Reading and Writing Local Disk

Demonstrating random I/O, this function reads a sector at a time backwards through a VMDK. If it sees the string “VmWare” it substitutes the string “VMware” in its place and writes the sector back to VMDK.

#include <string>

static void DoEdit(void)/

{

VixDisk disk(appGlobals.connection, appGlobals.diskPath, appGlobals.openFlags);

uint8 buf[VIXDISKLIB_SECTOR_SIZE];

VixDiskLibSectorType i;

string str;

for (i = appGlobals.numSectors; i >= 0; i--) {

VixError vixError;

vixError = VixDiskLib_Read(disk.Handle(), appGlobals.startSector + i, 1, buf);

CHECK_AND_THROW(vixError);

str = buf;

if (pos = str.find("VmWare", 0)) {

str.replace(pos, 5, "VMware");

buf = str;

vixError = VixDiskLib_Write(disk.Handle(), appGlobals.startSector + i, 1, buf);

CHECK_AND_THROW(vixError);

}

}

}

Reading and Writing Remote Disk

The DoEdit() function is similar for remote managed virtual disk on ESXi hosts, but beforehand you must call VixDiskLib_Connect() with authentication credentials instead of passing NULL parameters.

if (appGlobals.isRemote) {

cnxParams.vmxSpec = NULL;

cnxParams.serverName = appGlobals.host;

cnxParams.credType = VIXDISKLIB_CRED_UID;

cnxParams.creds.uid.userName = appGlobals.userName;

cnxParams.creds.uid.password = appGlobals.password;

cnxParams.port = appGlobals.port;

}

VixError vixError = VixDiskLib_Init(1, 0, NULL, NULL, NULL, NULL);

CHECK_AND_THROW(vixError);

vixError = VixDiskLib_Connect(&cnxParams, &appGlobals.connection);

Deleting a Disk (Unlink)

The function to delete virtual disk files is VixDiskLib_Unlink(). It takes two arguments: a connection and a VMDK filename.

vixError = VixDiskLib_Unlink(appGlobals.connection, appGlobals.diskPath);

Effects of Deleting a Virtual Disk

When you delete a VMDK, you lose all the information it contained. In most cases, the host operating system prevents you from doing this when a virtual machine is running. However, if you delete a VMDK with its virtual machine powered off, that guest OS becomes unbootable.

Renaming a Disk

The function to rename virtual disk files is VixDiskLib_Rename(). It takes two arguments: the old and the new VMDK filenames.

vixError = VixDiskLib_Rename(oldGlobals.diskpath, newGlobals.diskpath);

Effects of Renaming a Virtual Disk

The server expects VMDK files of its guest OS virtual machines to be in a predictable location. Any file accesses that occur during renaming might cause I/O failure and possibly cause a guest OS to fail.