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Message-ID: <CAMbhsRQ2EPEW+=0bhE6N9-dr44H8G_gzQ7h5LqOp7Lntr2RhTg@mail.gmail.com> Date: Sat, 21 Jul 2012 08:42:12 -0700 From: Colin Cross <ccross@...roid.com> To: Richard Purdie <richard.purdie@...uxfoundation.org> Cc: Greg KH <gregkh@...uxfoundation.org>, lkml <linux-kernel@...r.kernel.org>, Bryan Wu <bryan.wu@...onical.com> Subject: Re: sysfs permissions on dynamic attributes (led delay_on and delay_off) On Sat, Jul 21, 2012 at 4:21 AM, Richard Purdie <richard.purdie@...uxfoundation.org> wrote: > On Sat, 2012-07-21 at 01:26 -0700, Colin Cross wrote: >> On Sat, Jul 21, 2012 at 12:33 AM, Richard Purdie >> <richard.purdie@...uxfoundation.org> wrote: >> > On Fri, 2012-07-20 at 21:08 -0700, Greg KH wrote: >> >> On Fri, Jul 20, 2012 at 05:46:14PM -0700, Colin Cross wrote: >> >> > I'm trying to use the standard ledtrig-timer.c code to handle led >> >> > blinking for notifications on an Android device, and I'm hitting some >> >> > issues with setting permissions on the dynamically created delay_on >> >> > and delay_off attributes. For most sysfs files, we have userspace >> >> > uevent parser that watches for device add notifications and >> >> > chowns/chmods attributes. This doesn't work for delay_on and >> >> > delay_off, because they are created later, when "timer" is written to >> >> > the trigger attribute. There is no uevent when the new files are >> >> > created, and sysfs doesn't support inotify, so I don't see any way to >> >> > receive an event to set the permissions. This issue exists any time >> >> > that device_create_file is called after device_add. >> >> > >> >> > What is the appropriate way to get an event to set the permissions? >> >> > Add inotify support for sysfs file creation? Send a KOBJ_CHANGE >> >> > uevent in device_create_file? >> >> >> >> No. >> >> >> >> > Send a KOBJ_CHANGE uevent from the driver after calling >> >> > device_create_file? >> >> >> >> Yes. >> >> >> >> > Dynamically create a timer device under /sys/class/leds/<led> so a new >> >> > add uevent gets sent? >> >> >> >> Ick. >> >> >> >> > Promote blinking to be a core led feature instead of a trigger, so the >> >> > files are always present? >> >> >> >> That's the best thing, why not just do that? >> > >> > This implies we should make every trigger a core led feature and >> > effectively do away with triggers. I'm not sure that makes sense. >> >> Blinking is already effectively a core feature. It is implemented in >> led-core.c so it can be used by other triggers besides timer, it's >> state is stored in the led_classdev structure, not in the trigger >> data, and the only thing left in ledtrig-timer.c is the sysfs files. > > Having the attributes present all the time leads to some nasty questions > like how the on/off delays interact with things like say a network > activity trigger. Not all triggers are going to respect these delay > values and I can imagine a whole new set of nasty bug reports with no > easy solutions if this change is made... The delay_on and delay_off files could easily override the values from the trigger. Sending a KOBJ_CHANGE uevent is not a great solution, it's still horribly racy in userspace. This script would never work reliably: echo timer > trigger echo 1000 > delay_on echo 1000 > delay_off echo 255 > brightness -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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