Re: question on flushing buffers and spinning down disk
Alan Stern <[email protected]>
| Newsgroups | gmane.linux.usb.devel,gmane.linux.scsi |
|---|---|
| Message-ID | <[email protected]> |
On Fri, 28 Sep 2007, Oliver Neukum wrote: > Am Donnerstag 27 September 2007 schrieb Alan Stern: > > There's also a philosophical objection. Who is in a better position to > > judge when a device like a SCSI drive should be autosuspended: its own > > driver (sd) or someone else (usb-storage)? > > Then a philosophical answer. The highest entity which understands what > it is doing when using power management. Highest here to be understood > not as a position in the device tree, but in the flow of information. In this sense, sd is higher than usb-storage, right? Because I/O requests pass through sd first, then usb-storage, on their way to the device. My point is that when dealing with SCSI disks, sd understands the implications of Power Management better than usb-storage does. Similarly, when dealing with SCSI cd drives, sr understands the implications of Power Management better than usb-storage. Hence by your own argument, the SCSI high-level drivers should be responsible for autosuspending their respective devices. usb-storage, on the other hand, should be responsible only for suspending the transport, since that's what it does understand. > That is in our case usb-storage. Sr or sd can't do it because they don't > and can't understand power management. That's simply not true. If sd didn't understand Power Management then sd_suspend() and sd_resume() would be empty. > Now they might be asked to provide some helpers. An open count and > notifications about the state of the queue would be obvious. Other > suggestions? I still think you're trying to go about it all backwards. Alan Stern ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2005. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ [email protected] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel