2019年8月25日(日) 0:53 Jacek Anaszewski <jacek.anaszew...@gmail.com>: > > On 8/23/19 6:00 PM, Akinobu Mita wrote: > > 2019年8月20日(火) 3:38 Jacek Anaszewski <jacek.anaszew...@gmail.com>: > >> > >> On 8/19/19 8:22 PM, Jacek Anaszewski wrote: > >>> On 8/19/19 4:38 PM, Pavel Machek wrote: > >>>> On Sat 2019-08-17 22:07:43, Jacek Anaszewski wrote: > >>>>> On 8/17/19 4:55 PM, Pavel Machek wrote: > >>>>>> On Fri 2019-08-16 01:59:58, Akinobu Mita wrote: > >>>>>>> This allows LEDs to be controlled by block device activity. > >>>>>>> > >>>>>>> We already have ledtrig-disk (LED disk activity trigger), but the > >>>>>>> lower > >>>>>>> level disk drivers need to utilize ledtrig_disk_activity() to make the > >>>>>>> LED blink. > >>>>>>> > >>>>>>> The LED block device trigger doesn't require the lower level drivers > >>>>>>> to > >>>>>>> have any instrumentation. The activity is collected by polling the > >>>>>>> disk > >>>>>>> stats. > >>>>>>> > >>>>>>> Example: > >>>>>>> > >>>>>>> echo block-nvme0n1 > /sys/class/leds/diy/trigger > >>>>>> > >>>>>> Lets use one trigger "block" and have the device as a parameter, > >>>>>> please. > >>>>>> > >>>>>> We already have 1000 cpu triggers on 1000 cpu machines, and yes, its a > >>>>>> disaster we'll need to fix. Lets not repeat the same mistake here. > >>>>>> > >>>>>> I guess it may be slightly more work. Sorry about that. > >>>>> > >>>>> We should be able to list available block devices to set, > >>>>> so the problem would be not avoided anyway. > >>>> > >>>> Should we? We need to list triggers, but we may not list all the > >>>> devices... > >>> > >>> This is similar to usbport trigger that lists available > >>> ports as files in a sub-directory. We might eventually go > >>> in this direction. > >> > >> I must withdraw this statement. This is not similar to usbport > >> trigger. The difference is that with ledtrig-block we have separate > >> triggers per each device and I am not aware if there is some centralized > >> mechanism similar to blocking_notifier_chain (usb_notifier_list > >> in drivers/usb/core/notify.c) available for block devices, that > >> would allow to gather all available block devs under common trigger. > >> > >> Moreover I remember Greg once discouraged using notifier chains > >> as they are unsafe, so we would need some other solution anyway. > > > > I start thinking that we should implement the LED block device activity > > trigger in userspace. The userspace application firstly activates > > one-shot LED trigger and periodically reads /sys/block/<disk>/stat and > > writes /sys/class/leds/<led>/shot if there is any disk activity. > > This would suboptimal solution. I have another idea - let's get back > to the implementation of ledtrig-blk in genhd.c. We would be registering > one trigger on module initialization in a function with __init modifier. > Then we would need to add/remove triggers to the ledtrig-blk in > register_blkdev()/unregister_blkdev(). And registered triggers would > be listed in block_devs directory created by the trigger. > > You can compare how drivers/usb/core/ledtrig-usbport.c maintains > similar directory of usb ports.
It could be possible, but I have yet another idea. What about introducing /proc/led-triggers and /sys/class/leds/<led>/current-trigger? The /sys/class/leds/<led>/trigger will be obsoleted by these two files. The /proc/led-triggers is read only and no PAGE_SIZE limitation by the seq_file interface. So we can list all triggers in this file. The /sys/class/leds/<led>/current-trigger is almost identical to /sys/class/leds/<led>/trigger. The only difference is that 'current-trigger' only shows the current trigger name.
