From: Kay Sievers <kay.sievers@vrfy.org>
To: Nicolas Pitre <nicolas.pitre@canonical.com>
Cc: Greg Kroah-Hartman <gregkh@suse.de>,
linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 29/49] vcs: add poll/fasync support
Date: Wed, 10 Nov 2010 02:42:10 +0100 [thread overview]
Message-ID: <AANLkTinfLT0WYDHek8+QjYKfGC0rtJ3ZFhoZj2fD8-Ri@mail.gmail.com> (raw)
In-Reply-To: <alpine.LFD.2.00.1011092013290.13911@xanadu.home>
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
next prev parent reply other threads:[~2010-11-10 1:42 UTC|newest]
Thread overview: 71+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-22 17:51 [GIT PATCH] TTY/Serial merge for .37-rc1 Greg KH
2010-10-22 18:20 ` [PATCH 01/49] tty: add tty_struct->dev pointer to corresponding device instance Greg Kroah-Hartman
2010-10-22 18:20 ` [PATCH 02/49] serport: place serport serio device correctly in the device tree Greg Kroah-Hartman
2010-10-22 18:20 ` [PATCH 03/49] serial: mfd: snprintf() returns largish values Greg Kroah-Hartman
2010-10-22 18:20 ` [PATCH 04/49] serial: Add CONSOLE_POLL support for uartlite Greg Kroah-Hartman
2010-10-22 18:20 ` [PATCH 05/49] tty: Remove __GFP_NOFAIL from tty_add_file() Greg Kroah-Hartman
2010-10-22 18:20 ` [PATCH 06/49] ioctl: Use asm-generic/ioctls.h on arm (enables termiox) Greg Kroah-Hartman
2010-10-22 18:20 ` [PATCH 07/49] ioctl: Use asm-generic/ioctls.h on avr32 " Greg Kroah-Hartman
2010-10-22 18:20 ` [PATCH 08/49] ioctl: Use asm-generic/ioctls.h on cris " Greg Kroah-Hartman
2010-10-25 14:10 ` Jesper Nilsson
2010-10-22 18:20 ` [PATCH 09/49] ioctl: Use asm-generic/ioctls.h on frv " Greg Kroah-Hartman
2010-10-22 18:20 ` [PATCH 10/49] ioctl: Use asm-generic/ioctls.h on h8300 " Greg Kroah-Hartman
2010-10-22 18:20 ` [PATCH 11/49] ioctl: Use asm-generic/ioctls.h on ia64 " Greg Kroah-Hartman
2010-10-22 18:20 ` [PATCH 12/49] ioctl: Use asm-generic/ioctls.h on m32r " Greg Kroah-Hartman
2010-10-22 18:20 ` [PATCH 13/49] ioctl: Use asm-generic/ioctls.h on m68k " Greg Kroah-Hartman
2010-10-22 18:20 ` [PATCH 14/49] ioctl: Use asm-generic/ioctls.h on mn10300 " Greg Kroah-Hartman
2010-10-22 18:20 ` [PATCH 15/49] ioctl: Use asm-generic/ioctls.h on s390 " Greg Kroah-Hartman
2010-10-22 18:20 ` [PATCH 16/49] serial-core: skip call set_termios/console_start when no_console_suspend Greg Kroah-Hartman
2010-10-22 18:20 ` [PATCH 17/49] serial-core: restore termios settings when resume console ports Greg Kroah-Hartman
2010-10-22 18:20 ` [PATCH 18/49] add ttyprintk driver Greg Kroah-Hartman
2010-10-22 18:20 ` [PATCH 19/49] Char: mxser, call pci_disable_device from probe/remove Greg Kroah-Hartman
2010-10-22 18:20 ` [PATCH 20/49] tty_io: check return code of tty_register_device Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 21/49] serial: mrst_max3110: some code cleanup Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 22/49] serial: mrst_max3110: Make the IRQ option runtime Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 23/49] serial: max3107: Fix memory leaks when returning on error Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 24/49] tty: Make tiocgicount a handler Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 25/49] tty: Convert the USB drivers to the new icount interface Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 26/49] tty: icount changeover for other main devices Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 27/49] tty: Fix warning left over from TIOCGICOUNT changes Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 28/49] tty: Add a new file /proc/tty/consoles Greg Kroah-Hartman
2010-10-23 11:24 ` Jiri Slaby
2010-10-23 11:40 ` Jiri Slaby
2010-10-23 11:51 ` Al Viro
2010-10-23 12:00 ` Jiri Slaby
2010-10-23 12:26 ` Al Viro
2010-10-23 15:46 ` Greg KH
2010-10-23 16:53 ` Greg KH
2010-10-23 17:03 ` Greg KH
2010-10-23 12:04 ` Al Viro
2010-10-25 7:51 ` Dr. Werner Fink
2010-10-27 0:50 ` Al Viro
2010-10-27 9:27 ` Dr. Werner Fink
2010-10-27 9:51 ` Jiri Slaby
2010-10-27 11:31 ` Dr. Werner Fink
2010-10-23 11:46 ` Christoph Hellwig
2010-10-22 18:21 ` [PATCH 29/49] vcs: add poll/fasync support Greg Kroah-Hartman
2010-11-10 0:12 ` Kay Sievers
2010-11-10 1:26 ` Nicolas Pitre
2010-11-10 1:42 ` Kay Sievers [this message]
2010-11-10 6:33 ` Nicolas Pitre
2010-11-10 9:35 ` Kay Sievers
2010-10-22 18:21 ` [PATCH 30/49] vcs: invoke the vt update callback when /dev/vcs* is written to Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 31/49] tty: MAINTAINERS: add drivers/serial/jsm/ as maintained driver Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 32/49] serial: 8250: Don't delay after transmitter is ready Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 33/49] serial: mark the 8250 driver as maintained Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 34/49] serial: Factor out uart_poll_timeout() from 8250 driver Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 35/49] altera_uart: Add support for polling mode (IRQ-less) Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 36/49] altera_uart: Add support for getting mapbase and IRQ from resources Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 37/49] altera_uart: Add support for different address strides Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 38/49] altera_uart: Make it possible to use Altera UART and 8250 ports together Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 39/49] altera_uart: Fixup type usage of port flags Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 40/49] altera_uart: Fix missing prototype for registering an early console Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 41/49] altera_uart: Don't use plain integer as NULL pointer Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 42/49] 8250: allow platforms to override PM hook Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 43/49] Alchemy: Add UART PM methods Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 44/49] jsm: Remove the uart port on errors Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 45/49] serial: mfd: add more baud rates support Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 46/49] serial/imx: check that the buffer is non-empty before sending it out Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 47/49] serial: abstraction for 8250 legacy ports Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 48/49] serial: bfin_sport_uart: speed up sport RX sample rate to be 3% faster Greg Kroah-Hartman
2010-10-22 18:21 ` [PATCH 49/49] serial8250: ratelimit "too much work" error Greg Kroah-Hartman
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