IRP_MJ_CREATE_MAILSLOT (FS and filter drivers)
When Sent
The I/O Manager sends the IRP_MJ_CREATE_MAILSLOT request when a new mailslot is being created or opened. Normally this IRP is sent:
- On behalf of a user-mode application that has called a Microsoft Win32 function such as CreateMailslot.
- Or, on behalf of a kernel-mode component that has called IoCreateFile or IoCreateFileSpecifyDeviceObjectHint.
If the mailslot create request is completed successfully, the application or kernel-mode component receives a handle to the mailslot file instance.
The handling of IRP_MJ_CREATE_MAILSLOT is much the same as IRP_MJ_CREATE.
Operation: File System Drivers
If the target device object is the file system's control device object, the file system driver's dispatch routine must do the following operations:
- Set Irp->IoStatus.Status and Irp->IoStatus.Information to appropriate values.
- Complete the IRP and return an appropriate NTSTATUS value.
Otherwise, the file system driver should process the create request.
Operation: Legacy File System Filter Drivers
If the target device object is the legacy filter driver's control device object, that driver's dispatch routine must complete the IRP and return an appropriate NTSTATUS value, after setting Irp->IoStatus.Status and Irp->IoStatus.Information to appropriate values.
Otherwise, the legacy filter driver should perform any needed processing. Depending on the nature of the filter, it should either complete the IRP or pass it down to the next-lower driver on the stack.
Generally, legacy filter drivers shouldn't return STATUS_PENDING in response to IRP_MJ_CREATE_MAILSLOT. However, if a lower-level driver returns STATUS_PENDING, the legacy filter driver should pass this status value up the driver chain.
Parameters
A file system or legacy filter driver calls IoGetCurrentIrpStackLocation with the given IRP to get a pointer to its own stack location in the IRP. In the following parameters, Irp points to the IRP and IrpSp points to the IO_STACK_LOCATION. The driver can use the information that is set in the following members of the IRP and the IRP stack location to process a create mailslot request.
DeviceObject is a pointer to the target device object.
Irp->Flags is set to the following flags for this request:
- IRP_CREATE_OPERATION
- IRP_DEFER_IO_COMPLETION
- IRP_SYNCHRONOUS_API
Irp->IoStatus points to an IO_STATUS_BLOCK structure that receives the final completion status and information about the requested operation. The file system sets the Information member of this structure to one of the following values:
- FILE_CREATED
- FILE_OPENED
Irp->RequestorMode indicates the execution mode of the process that requested the operation, either KernelMode or UserMode. If the SL_FORCE_ACCESS_CHECK flag is set, access checks must be performed, even if Irp->RequestorMode is KernelMode.
IrpSp->MajorFunction is set to IRP_MJ_CREATE_MAILSLOT.
IrpSp->Flags can be set to SL_FORCE_ACCESS_CHECK. If this flag is set, access checks must be performed even if the value of Irp->RequestorMode is KernelMode.
*IrpSp->Parameters.CreateMailslot.SecurityContext->AccessState is a pointer to an ACCESS_STATE structure containing the object's subject context, granted access types, and remaining desired access types.
IrpSp->Parameters.CreateMailslot.SecurityContext->DesiredAccess is an ACCESS_MASK structure specifying access rights requested for the mailslot. For more information, see the description of the DesiredAccess parameter to IoCreateFileSpecifyDeviceObjectHint.
IrpSp->Parameters.CreateMailslot.Options is a bitmask of flags that specify the options to be applied when creating or opening the mailslot, and the action to be taken if the mailslot already exists.
The high 8 bits of this parameter correspond to the Disposition parameter to IoCreateFileSpecifyDeviceObjectHint.
The low 24 bits of this member correspond to the CreateOptions parameter to IoCreateFileSpecifyDeviceObjectHint.
IrpSp->Parameters.CreateMailslot.ShareAccess is a bitmask of share access rights requested for the mailslot. If this member is zero, exclusive access is being requested. For more information, see the description of the ShareAccess parameter to IoCreateFileSpecifyDeviceObjectHint.
IrpSp->Parameters.CreateMailslot.Parameters is a pointer to a MAILSLOT_CREATE_PARAMETERS structure that contains the create parameters for when the mailslot is being created.
IrpSp->FileObject is a pointer to a file object that the I/O Manager creates to represent the mailslot to be created or opened. When the file system processes the IRP_MJ_CREATE_MAILSLOT request, it sets the FsContext and possibly FsContext2 fields in this file object to values that are file-system-specific. Thus the values of the FsContext and FsContext2 fields can't be considered valid until after the file system has processed the create request. For more information, see File Streams, Stream Contexts, and Per-Stream Contexts.
IoCancelFileOpen (and FltCancelFileOpen) set the FO_FILE_OPEN_CANCELLED flag in the file object's Flags field. Setting this flag indicates that the IRP_MJ_CREATE_MAILSLOT request has been canceled, and an IRP_MJ_CLOSE request will be issued for this file object. Once the create request has been canceled, it can't be reissued.
The IrpSp->FileObject parameter contains a pointer to the RelatedFileObject field, which is also a FILE_OBJECT structure. The RelatedFileObject field of a FILE_OBJECT structure is used to indicate that a given mailslot has been opened relative to an already open file object. This usually indicates that the relative file is a directory but stream-based files may be opened relative to an already existing stream of a file. The RelatedFileObject field of the FILE_OBJECT structure is only valid during the processing of IRP_MJ_CREATE_MAILSLOT.
See also
FLT_PARAMETERS for IRP_MJ_CREATE_MAILSLOT
IoCreateFileSpecifyDeviceObjectHint