Messages in this thread | | | From | Kay Sievers <> | Date | Wed, 10 Nov 2010 02:42:10 +0100 | Subject | Re: [PATCH 29/49] vcs: add poll/fasync support |
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On Wed, Nov 10, 2010 at 02:26, Nicolas Pitre <nicolas.pitre@canonical.com> wrote: > On Wed, 10 Nov 2010, Kay Sievers wrote: > >> On Fri, Oct 22, 2010 at 20:21, Greg Kroah-Hartman <gregkh@suse.de> wrote: >> > From: Nicolas Pitre <nico@fluxnic.net> >> > >> > The /dev/vcs* devices are used, amongst other things, by accessibility >> > applications such as BRLTTY to display the screen content onto refreshable >> > braille displays. Currently this is performed by constantly reading from >> > /dev/vcsa0 whether or not the screen content has changed. Given the >> > default braille refresh rate of 25 times per second, this easily qualifies >> > as the biggest source of wake-up events preventing laptops from entering >> > deeper power saving states. >> > >> > To avoid this periodic polling, let's add support for select()/poll() and >> > SIGIO with the /dev/vcs* devices. The implemented semantic is to report >> > data availability whenever the corresponding vt has seen some update after >> > the last read() operation. The application still has to lseek() back >> > as usual in order to read() the new data. >> >> Shouldn't it raise POLLPRI/POLLERR then, when it's not about new data >> to read? We do this for several files in the kernel where we just want >> to wakup someone, but the pretty well-defined semantics of poll() >> don't apply. > > Hmmm... Maybe POLLPRI, but POLLERR makes no sense.
I have no opinion about that, but it's what others do: http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=31b07093c44a7a442394d44423e21d783f5523b8 http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=4508a7a734b111b8b7e39986237d84acb1168dd0
The POLLIN should definitely go, it's POSIX defined. What we do here is more like an error that wakes up than a stream data to read. :)
Kay -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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