Enumerate the \?? (\DosDevices) directory

[Magnus Wennergren]

I am currently writning a COM-redirector for Windows NT. When I create the
symbolic links in my DriverEntry, I need to know which COMx names that are
already in use. If I try to create a link that already exist, the system
crashes.

Is there a way to enumerate the symbolic links from my kernel-mode driver?

/Magnus

[Lukasz Foltyn]

Try to use ZwQuerySymbolicLinkObject, to test if a symbolic
link already exists.
Prototype is:

NTSYSAPI NTSTATUS NTAPI ZwQuerySymbolicLinkObject( HANDLE Handle,
PUNICODE_STRING
LinkName, PUINT SymLinkLen );

Lukasz Foltyn

Magnus Wennergren <magnus.w...@axis.com> wrote in message
news:7kj3tr$ff...@news.ajou.ac.kr...

[Jamey kirby]

Use QueryDosDevice()

[Walter Oney]

Jamey kirby wrote:
> Use QueryDosDevice()

But he wanted to do it in kernel-mode...

What people usually do is just construct names in a loop and wait until
IoCreateDevice or IoCreateSymbolicLink succeeds. Neither of them should
crash the system just because given an existing name -- they return an
error status.

--
Walter Oney
http://www.oneysoft.com

[Jamey kirby]

Ooops... :)

Walter Oney wrote in message <376FB27D...@oneysoft.com>...

[Jamey kirby]

Here is code I use to enumerate drive letters in KM. Maybe this can be
adopted

// FindAvailableDriveLetter()
NTSTATUS FindAvailableDriveLetter
(
PUCHAR DriveLetter
)
{
NTSTATUS ntStatus;

UNICODE_STRING ntUnicodeString;
CCHAR ntNameBuffer[MAXIMUM_FILENAME_LENGTH];
STRING ntNameString;
OBJECT_ATTRIBUTES attributes;
HANDLE directoryHandle;
HANDLE linkHandle = NULL;
ULONG i;

PAGED_CODE();

// Open the Win32 object name-space directory
RtlInitUnicodeString(&ntUnicodeString, (PWCHAR)L"\\DosDevices");

InitializeObjectAttributes
(
&attributes,
&ntUnicodeString,
OBJ_CASE_INSENSITIVE,
NULL,
NULL
);

ntStatus = ZwOpenDirectoryObject
(
&directoryHandle,
DIRECTORY_QUERY,
&attributes
);

if (!NT_SUCCESS(ntStatus))
{
RtlInitUnicodeString(&ntUnicodeString, (PWCHAR)L"\\??");

InitializeObjectAttributes
(
&attributes,
&ntUnicodeString,
OBJ_CASE_INSENSITIVE,
NULL,
NULL
);

ntStatus = ZwOpenDirectoryObject
(
&directoryHandle,
DIRECTORY_QUERY,
&attributes
);

if (!NT_SUCCESS(ntStatus))
{
goto FindAvailableDriveLetterExit;
}
}

// Open symbolic link object(s)
for (i = 2; i < 26; i++)
{
sprintf(ntNameBuffer, "%C:", i + 'A');
RtlInitString(&ntNameString, ntNameBuffer);

ntStatus = RtlAnsiStringToUnicodeString
(
&ntUnicodeString,
&ntNameString,
TRUE
);

if (!NT_SUCCESS(ntStatus))
break;

InitializeObjectAttributes
(
&attributes,
&ntUnicodeString,
OBJ_CASE_INSENSITIVE,
directoryHandle,
NULL
);

ntStatus = ZwOpenSymbolicLinkObject
(
&linkHandle,
SYMBOLIC_LINK_QUERY,
&attributes
);

if (!NT_SUCCESS(ntStatus))
{
*DriveLetter = (CHAR)((CHAR)i + (CHAR)'A');
ntStatus = STATUS_SUCCESS;
}
else
{
ZwClose(linkHandle);
ntStatus = STATUS_OBJECT_NAME_COLLISION;
}

RtlFreeUnicodeString(&ntUnicodeString);

if (NT_SUCCESS(ntStatus))
break;
}

ZwClose(directoryHandle);

FindAvailableDriveLetterExit:

return (ntStatus);