Say you have the path to a file and you want to access the volume that the file resides on.<\/p>\n
Warning<\/b>: All error checking is removed for expository purposes.<\/p>\n
The first step on our journey is getting from the path to the volume mount point. This tells us where the root of the volume got inserted into the namespace.<\/p>\n
TCHAR volumePath[MAX_PATH]; \/\/ for expository purposes\r\nGetVolumePathName(filePath, volumePath, ARRAYSIZE(volumePath));\r\n<\/pre>\nThis information might be useful in its own right, but for us, it’s just a stepping stone to the next piece of information: The volume name.<\/p>\n
TCHAR volumeName[MAX_PATH]; \/\/ for expository purposes\r\nGetVolumeNameForVolumeMountPoint(volumePath, volumeName, ARRAYSIZE(volumeName));\r\n<\/pre>\nThe volume name is returned in the form \\\\?\\Volume{guid}\\<\/tt>, with a trailing backslash. Note that this call will fail if the path is not a local drive.<\/p>\n
Now things get weird.<\/p>\n
If you pass that path to the
CreateFile<\/code> function with the trailing backslash intact, then you are opening a handle to the root directory of the volume.<\/p>\nIf you pass that path to the
CreateFile<\/code> function with the trailing backslash removed, then you are opening a handle to the volume itself.<\/p>\nDepending on which operation you want to perform on the volume, you either must have or must not have that trailing backslash.<\/p>\n
In our case, we want to open a handle to the volume itself, so we need to remove that trailing backslash. The call to
CreateFile<\/code> looks like this:<\/p>\nHANDLE handle = CreateFile(volumeNameWithoutTrailingBackslash,\r\n 0, \/* no special access requested *\/\r\n FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,\r\n nullptr, \/* no custom security *\/\r\n OPEN_EXISTING,\r\n FILE_FLAG_BACKUP_SEMANTICS,\r\n nullptr); \/* template *\/\r\n<\/pre>\nVolume query operations do not require any specific level of access, so we’ll ask for no special access. Which is good, because regular non-elevated code doesn’t really have much in the way of special access to volumes. You won’t able to get
GENERIC_<\/code>READ<\/code>, much lessGENERIC_<\/code>WRITE<\/code>. (You’ll be able to getFILE_<\/code>READ_<\/code>ATTRIBUTES<\/code>, if that’s any consolation.)<\/p>\nYou also need to request backup semantics in order to open a volume.<\/p>\n