On Mon, 27 Apr 2020, Greg KH wrote: > On Sun, Apr 26, 2020 at 03:08:38PM -0400, Dave Mielke wrote: > > We're working on getting brltty to run as an unprivileged user with just a few > > required capabilities. We don't want one of those required capabilities to be > > CAP_DAC_OVERRIDE (bypass file permission checks). > > > > Some USB-connected braille devices don't respond very well to being > > autosuspended. We get around this, when running as root, by writing to the > > SYSFS power/autosuspend file associated with the device. Our problem is that > > only the root user can write to it. > > > > Other than using CAP_DAC_OVERRIDE (which we don't want to do), what other > > way(s) might we be able to use to overcome this restriction? For example, is > > there some kind of safe (enough) udev rule? > > Have a udev rule that turns autosuspend off for each specific USB device > that you know does not work with autosuspend. Do you have such a list? > > If so, we can add it to the USB core with the > USB_QUIRK_DISCONNECT_SUSPEND flag. Or is it the USB_QUIRK_NO_LPM that > they need? I can't remember, but you can test it out from userspace > by reading about those in the > Documentation/admin-guide/kernel-parameters.txt file. A udev rule will probably work a lot better than a quirk flag. In fact, I don't think we have a quirk flag for "don't autosuspend". DISCONNECT_SUSPEND doesn't affect autosuspends, only system sleeps. And NO_LPM only affects USB-3 devices. A suitable udev rule should be pretty easy to write. Alan Stern
