Lagringsklassdrivrutinens releaseQueue-rutin

Unless a storage class driver ORs the SrbFlags for a given request with SRB_FLAGS_NO_QUEUE_FREEZE, the system port driver freezes a queue for a given logical unit after any of the following:

• En bussåterställning inträffade när den logiska enheten körde en begäran.

• The logical unit returned SCSISTAT_CHECK_CONDITION or SCSISTAT_COMMAND_TERMINATED, which the class driver can find in the SRB's ScsiStatus member.

• En begäran har överskriden tidsgräns.

• En begäran avslutades av ett bussmeddelandekommando, till exempel SCSIMESS_ABORT.

The port driver indicates that an LU-specific queue has been frozen by returning a request with SRB_STATUS_QUEUE_FROZEN in the SrbStatus member. Nya begäranden från klassdrivrutinen kan infogas i kön, men endast autosense-begäranden skickas till den logiska enheten så länge kön är låst.

Om du fryser kön under dessa förhållanden kan varje drivrutin för lagringsklass analysera ett fel innan andra jobb i kö körs. Till exempel kan köade jobb behöva avbrytas om mediet har ändrats. To flush the queue, the driver can send a request with the SrbFlags ORed with SRB_FLAGS_BYPASS_FROZEN_QUEUE.

A ReleaseQueue routine allocates and sets up an IRP and an SRB to either release or flush a frozen queue. The Function member of the SRB must be set to SRB_FUNCTION_RELEASE_QUEUE or SRB_FUNCTION_FLUSH_QUEUE, which both releases a frozen queue and cancels all currently queued requests for the target logical unit. The port driver completes all requests in a flushed queue with their SrbStatus members set to SRB_STATUS_REQUEST_FLUSHED.

Failing to release a frozen queue makes the device inaccessible, so a driver's ReleaseQueue routine should be designed to succeed even in low memory conditions. A ReleaseQueue routine should first attempt to allocate memory for an SRB by calling ExAllocatePool with the NonPagedPool memory type and, if that allocation fails, use an SRB that was preallocated during driver initialization. Om drivrutinen allokerar en SRB att hålla i reserven när den initierar sitt enhetstillägg, enligt beskrivningen i Konfigurera en lagringsklassdrivrutins enhetstillägg, kan dess ReleaseQueue använda den SRB om minnespoolen är låg, med en lämplig synkroniseringsmekanism om flera samtidiga versionsåtgärder skulle behövas.

Note that a class driver's ReleaseQueue routine is called asynchronously, generally from its IoCompletion routine. A class driver's IoCompletion routine cannot call ReleaseQueue to flush a queue that is not frozen. However, it can call ReleaseQueue to release an unfrozen queue, and the port driver simply ignores such a request.