The operating system sends an IRP_MJ_CREATE request to open a handle to a file object or device object. For example, when a driver calls ZwCreateFile, the operating system sends an IRP_MJ_CREATE request to perform the actual open operation.
The Parameters.Create.SecurityContext member points to an IO_SECURITY_CONTEXT structure that describes the security context for the request. The Parameters.Create.SecurityContext->DesiredAccess member is an access mask that specifies the access rights that are being requested by the caller.
The Parameters.Create.Options member is a ULONG value that describes the options that are used when opening the handle. The high 8 bits correspond to the value of the CreateDisposition parameter of ZwCreateFile, and the low 24 bits correspond to the value of the CreateOptions parameter of ZwCreateFile.
The Parameters.Create.ShareAccess member is a USHORT value that describes the type of share access. This value corresponds to the value of the ShareAccess parameter of ZwCreateFile.
The Parameters.Create.FileAttributes and Parameters.Create.EaLength members are reserved for use by file systems and file system filter drivers. For more information, see the IRP_MJ_CREATE topic in the Installable File System (IFS) documentation.
Most device and intermediate drivers set STATUS_SUCCESS in the I/O status block of the IRP and complete the create request, but drivers can optionally use their DispatchCreate routine to reserve resources for any subsequent I/O requests for that handle. For example, the system serial driver maps its paged-out code and allocates any resources that are necessary to handle subsequent I/O requests for the user-mode thread that is attempting to open the device for input and output.