IRP_MJ_QUERY_QUOTA (FS and filter drivers)
The I/O Manager sends the IRP_MJ_QUERY_QUOTA request. This request can be sent, for example, when a user-mode application has called a Win32 method such as IDiskQuotaControl::GetQuotaState.
If the file system supports disk quotas, the file system driver should extract and decode the file object to determine whether it represents a user open of a file or directory. If it does, the driver should process the query and complete the IRP. Otherwise, the driver should complete the IRP as appropriate without processing the query.
The filter driver should pass this IRP down to the next-lower driver on the stack, unless it needs to explicitly override quota behavior.
A file system or filter driver calls IoGetCurrentIrpStackLocation for 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 query quota information request:
DeviceObject is a pointer to the target device object.
DeviceObject->Flags: The DO_BUFFERED_IO and DO_DIRECT_IO flags are used as follows to specify the method by which data is passed to the driver:
Flag Setting I/O Method ~DO_BUFFERED_IO ~DO_DIRECT_IO METHOD_NEITHER ~DO_BUFFERED_IO DO_DIRECT_IO METHOD_DIRECT DO_BUFFERED_IO ~DO_DIRECT_IO METHOD_BUFFERED DO_BUFFERED_IO DO_DIRECT_IO METHOD_BUFFERED Irp->AssociatedIrp.SystemBuffer points to a system-supplied buffer to be used as an intermediate system buffer, if the DO_BUFFERED_IO flag is set in DeviceObject->Flags. Otherwise, this member is set to NULL.
Irp->IoStatus points to an IO_STATUS_BLOCK structure that receives the final completion status and information about the requested operation.
*Irp->UserBuffer points to a caller-supplied FILE_QUOTA_INFORMATION-structured output buffer that receives the quota information for the volume.
IrpSp->FileObject points to the file object that is associated with DeviceObject.
The IrpSp->FileObject parameter contains a pointer to the RelatedFileObject field, which is also a FILE_OBJECT structure. The RelatedFileObject field of the FILE_OBJECT structure isn't valid during the processing of IRP_MJ_QUERY_QUOTA and shouldn't be used.
IrpSp->Flags can be one or more of the following values:
| Flag | Meaning |
|---|---|
| SL_INDEX_SPECIFIED | Begin the scan at the entry in the quota list whose index is given by IrpSp->Parameters.QueryQuota.StartSid |
| SL_RESTART_SCAN | Begin the scan at the first entry in the list. If this flag isn't set, resume the scan from a previous IRP_MJ_QUERY_QUOTA request. |
| SL_RETURN_SINGLE_ENTRY | Return only the first entry that is found. |
IrpSp->MajorFunction is set to IRP_MJ_QUERY_QUOTA.
IrpSp->Parameters.QueryQuota.Length is the length, in bytes, of the buffer pointed to by Irp->UserBuffer.
IrpSp->Parameters.QueryQuota.SidList is an optional pointer to a list of SIDs whose quota information is to be returned. Each entry in the list is a FILE_GET_QUOTA_INFORMATION structure. This structure is defined as follows:
typedef struct _FILE_GET_QUOTA_INFORMATION { ULONG NextEntryOffset; ULONG SidLength; SID Sid; } FILE_GET_QUOTA_INFORMATION, *PFILE_GET_QUOTA_INFORMATION;
| Member | Meaning |
|---|---|
| NextEntryOffset | Byte offset of the next FILE_GET_QUOTA_INFORMATION entry, if multiple entries are present in a buffer. This member is zero if no other entries follow this one. |
| SidLength | Length, in bytes, of the Sid member. |
| Sid | Security identifier (SID) |
IrpSp->Parameters.QueryQuota.SidListLength is the length, in bytes, of the list of SIDs, if one is specified.
IrpSp->Parameters.QueryQuota.StartSid is an optional pointer to a SID that indicates that the returned information is to start with an entry other than the first. This parameter is ignored if a SID list is specified.