On Tue, Feb 23 2010, Alan Stern wrote: > On Tue, 23 Feb 2010, Jens Axboe wrote: > > > > P.S.: Jens, given a pointer to a struct gendisk or to a struct > > > request_queue, is there a good way to tell whether there any dirty > > > buffers for that device waiting to be written out? This is for > > > purposes of runtime power management -- in the initial implementation, > > > I want to avoid powering-down a block device if it is open or has any > > > dirty buffers. In other words, only completely idle devices should be > > > powered down (a good example would be a card reader with no memory card > > > inserted). > > > > There's no fool proof way. For most file systems I think you could get > > away with checking the q->bdi dirty lists to see if there's anything > > pending. But that wont work always, if the fs uses a different backing > > dev info than then queue itself. > > That's not what I meant. Dirty buffers on a filesystem make no > difference because they always get written out when the filesystem is > unmounted. The device file remains open as long as the filesystem > is mounted, which would prevent the device from being powered down. > > I was asking about dirty buffers on a block device that isn't holding a > filesystem -- where the raw device is being used directly for I/O. OK, so just specifically the page cache of the device. Is that really enough of an issue to warrant special checking? I mean, what normal setup would even use buffer raw device access? But if you wanted, I guess the only way would be to lookup dirty/writeback pages on the bdev inode mapping. For that you'd need the bdev, not the gendisk or the queue though. -- Jens Axboe _______________________________________________ linux-pm mailing list linux-pm@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/linux-pm
