WHDC PowerPoint Template Notes & Handouts

WHDC PowerPoint Template Notes & Handouts
Saturday, June 16, 2018 Writing SCSIPORT Miniport Drivers Sid Sidhartha Software Design Engineer Windows Driver Experience

Contents WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 SCSIPORT Architecture overview SCSI Miniport model PNP/Power handling for miniport I/O handling for miniport Common Miniport Errors Debugging SCSI Miniports Resources

Need For SCSI Miniports
WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 Windows Device Driver Model is complex PNP/POWER handling for bus drivers is involved Storage vendors need to focus on writing hardware specific code, not on Windows intricacies A WDM storage driver needs to handle performance, queuing, forward progress under low memory conditions and complex synchronization problems

Advantages Of A Miniport model
WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 No synchronization issues No PNP/Power complexity Simple interface to help concentrate on actually programming the hardware Miniport shielded from OS changes

Miniport Synchronization
WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 SCSIPORTStartIO Interrupt Levels Level 14 USB Miniport Level 13 Level 12 Level 11 HwStartIO Level 10

Miniport Synchronization Issues
WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 Advantages Miniport becomes simple to write No synchronization primitives needed Disadvantages Every time any Miniport routine is called, all interrupts at that level are blocked Polling by calling “StallExecution” is not desirable

PNP Support WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 Interrupts, ports, memory for the adapter are provided to the miniport during startup and restart During a Disable/Stop, port ensures disconnecting the interrupt, freeing the resources, etc. Port supports hot plug by providing SCSIPORTNotification (BusChangeDetected) call SCSI inquiry command is used to discover LUNs Port generates unique PNP-ID-based on inquiry string

PNP Gotchas WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 SCSIPORTNotification (BusChangeDetected) is not a synchronous call The dead LUN could get lot of IO before finally being removed from the OS The whole bus is scanned again and all the devices inquired Device enumeration is an expensive operation

POWER Support WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 Port provides idle detection support for disk LUNS are powered on/off by START_STOP_UNIT Command Power to the adapter is controlled by HwScsiAdapterControl call Port driver manages all S-D IRP translations and calls miniport only during adapter start and shutdown

IO: DMA Support WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 Miniport is shielded from OS DMA routines Miniport is provided with a physically contiguous common buffer that may be shared between CPU and bus-master HBA Simple interface to obtain physical address of the common buffer A per request storage area is also allocated for the Miniport

IO: Tags And Queue Management
WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 Tags generated for I/O are on a per Adapter basis Untagged requests cause port to wait for all active I/O on the LUN to complete NextRequest / NextLuRequest, are the mechanisms for Miniport to request more I/O For LUNS that support tagged queuing, use NextLuRequest to maximize throughput

I/O: Busy Processing WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 SCSIPORT supports busy processing on a LUN as opposed to adapter Level LUN transitions to a busy state when a SRB is completed with status BUSY All requests to the LUN are stopped, and the busy request is retried after 1s Miniport must call NextRequest in response to every request being returned as Busy

I/O: Bus Resets WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 Large I/O delays lead to miniport’s HwResetBus routine being called Miniport should ensure completion of all outstanding requests in this routine No more requests are issued to the miniport for a Reset Hold Period (currently 4s) The SCSI bus may also be reset to restart a hung adapter

Callbacks WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 MiniPort may request timer callbacks MiniPort may request a callback at DPC level from it’s ISR CallDisableInterrupts / CallEnableInterrupts should be used with care

Error Processing WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 Set the SrbStatus field wisely Use SCSIPORTLogError to log real adapter/link errors, not LUN failures Update the DataTransferLength field of the SRB appropriately Fill in the SenseData carefully

Important Registry Keys
WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 NumberOfRequests TotalSenseDataBytes TimeoutValue DriverParameter(s) ResetHoldTime MaximumSGList

Debugging: Tools WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 Debugger Extensions scsikd.dll Windows 2000, Windows XP, Windows Server 2003. minipkd.dll Windows Server 2003 only. SCSI Verifier Windows XP and Windows Server 2003 only.

Debugging: SCSI Verifier
WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 SCSI verifier is a great debugging and testing aid for miniport developers Verifier thunks calls to miniport for maintaining state Verifier bug-checks with a unique error code in case of rule violations Verifier does advanced error detection like remapping SRB extensions to physically non-contiguous pages

Debugging: Locating Adapters/LUNS
WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 0: kd> !object \device\scsi Object: e12a2520 Type: (863d12c8) Directory ObjectHeader: e12a2508 HandleCount: 0 PointerCount: 9 Directory Object: e Name: Scsi Hash Address Type Name Device adpu160m1Port3Path0Target6Lun0 Device adpu160m1Port3Path0Target1Lun0 a70 Device lp6nds351 e6040 Device adpu160m1Port3Path0Target0Lun0

Debugging: Locating Adapters/LUNS
WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 0: kd> !minipkd.adapters Adapter \Driver\lp6nds DO 86334a DevExt 86334b28 Adapter \Driver\adpu160m DO 8633da DevExt 8633db28 LUN c ev pnp(00/ff) pow(0,0) DevObj 862e6040 LUN c ev p d pnp(00/ff) pow(0,0) DevObj LUN c ev pnp(00/ff) pow(0,0) DevObj 862e5040 LUN ev pnp(00/ff) pow(0,0) DevObj Adapter \Driver\adpu160m DO DevExt f8 Flags c - claimed m - missing e - enumerated v - visible p – paging d – dump h - hibernate

Common Problems WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 Bugcheck 0x7A and 0x77 Hangs and timeouts Reproducible problems Interrupt storms and no interrupts Scatter gather lists

Common Problems: Bug-Check 7A/77
WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 Reset due to device/port timeout Selection timeout Controller errors !scsikd.classext displays LUN error log !errlog often identifies useful info

Common Problems: Hangs And Timeouts
WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 SCSIPORT DPC not running !pcr, !stacks, !process 0 7 Miniport fails to ask for next request !devobj <FDO>, !scsikd.scsiext Request is stuck in SCSIPORT Waiting for map registers

Common Problems: Interrupts
WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 Problems No interrupts Interrupt storms What to do… Check if your interrupt is shared Step over ISR to see if hardware is generating interrupt storm

Resources WHDC PowerPoint Template Notes & Handouts Saturday, June 16, 2018 Microsoft Windows DDK Debugging tools OSR’S NTDEV mailing list Links

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