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Date:	Sun, 2 May 2010 23:23:30 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Arve Hjønnevåg <arve@...roid.com>
Cc:	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Alan Stern <stern@...land.harvard.edu>,
	Tejun Heo <tj@...nel.org>, Oleg Nesterov <oleg@...hat.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ryusuke Konishi <konishi.ryusuke@....ntt.co.jp>,
	Jim Collar <jim.collar@...are.net>,
	"Greg Kroah-Hartman" <gregkh@...e.de>, Avi Kivity <avi@...hat.com>,
	Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
	Magnus Damm <damm@...l.co.jp>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Nigel Cunningham <nigel@...onice.net>,
	linux-doc@...r.kernel.org
Subject: Re: [PATCH 2/8] PM: suspend_block: Add driver to access suspend blockers from user-space

On Saturday 01 May 2010, Arve Hjønnevåg wrote:
> Add a misc device, "suspend_blocker", that allows user-space processes
> to block auto suspend. The device has ioctls to create a suspend_blocker,
> and to block and unblock suspend. To delete the suspend_blocker, close
> the device.
> 
> Signed-off-by: Arve Hjønnevåg <arve@...roid.com>
> ---
>  Documentation/ioctl/ioctl-number.txt          |    3 +-
>  Documentation/power/opportunistic-suspend.txt |   17 ++++
>  include/linux/suspend_block_dev.h             |   25 +++++
>  kernel/power/Kconfig                          |    9 ++
>  kernel/power/Makefile                         |    1 +
>  kernel/power/user_suspend_blocker.c           |  128 +++++++++++++++++++++++++
>  6 files changed, 182 insertions(+), 1 deletions(-)
>  create mode 100644 include/linux/suspend_block_dev.h
>  create mode 100644 kernel/power/user_suspend_blocker.c
> 
> diff --git a/Documentation/ioctl/ioctl-number.txt b/Documentation/ioctl/ioctl-number.txt
> index dd5806f..e2458f7 100644
> --- a/Documentation/ioctl/ioctl-number.txt
> +++ b/Documentation/ioctl/ioctl-number.txt
> @@ -254,7 +254,8 @@ Code  Seq#(hex)	Include File		Comments
>  'q'	80-FF	linux/telephony.h	Internet PhoneJACK, Internet LineJACK
>  		linux/ixjuser.h		<http://www.quicknet.net>
>  'r'	00-1F	linux/msdos_fs.h and fs/fat/dir.c
> -'s'	all	linux/cdk.h
> +'s'	all	linux/cdk.h	conflict!
> +'s'	all	linux/suspend_block_dev.h	conflict!
>  't'	00-7F	linux/if_ppp.h
>  't'	80-8F	linux/isdn_ppp.h
>  't'	90	linux/toshiba.h
> diff --git a/Documentation/power/opportunistic-suspend.txt b/Documentation/power/opportunistic-suspend.txt
> index 3d060e8..f2b145e 100644
> --- a/Documentation/power/opportunistic-suspend.txt
> +++ b/Documentation/power/opportunistic-suspend.txt
> @@ -117,3 +117,20 @@ if (list_empty(&state->pending_work))
>  else
>  	suspend_block(&state->suspend_blocker);
>  
> +User-space API
> +==============
> +
> +To create a suspend_blocker from user-space, open the suspend_blocker device:
> +    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
> +then call:
> +    ioctl(fd, SUSPEND_BLOCKER_IOCTL_INIT(strlen(name)), name);
> +
> +To activate a suspend_blocker call:
> +    ioctl(fd, SUSPEND_BLOCKER_IOCTL_BLOCK);
> +
> +To unblock call:
> +    ioctl(fd, SUSPEND_BLOCKER_IOCTL_UNBLOCK);
> +
> +To destroy the suspend_blocker, close the device:
> +    close(fd);
> +
> diff --git a/include/linux/suspend_block_dev.h b/include/linux/suspend_block_dev.h
> new file mode 100644
> index 0000000..24bc5c7
> --- /dev/null
> +++ b/include/linux/suspend_block_dev.h
> @@ -0,0 +1,25 @@
> +/* include/linux/suspend_block_dev.h
> + *
> + * Copyright (C) 2009 Google, Inc.
> + *
> + * This software is licensed under the terms of the GNU General Public
> + * License version 2, as published by the Free Software Foundation, and
> + * may be copied, distributed, and modified under those terms.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + */
> +
> +#ifndef _LINUX_SUSPEND_BLOCK_DEV_H
> +#define _LINUX_SUSPEND_BLOCK_DEV_H
> +
> +#include <linux/ioctl.h>
> +
> +#define SUSPEND_BLOCKER_IOCTL_INIT(len)		_IOC(_IOC_WRITE, 's', 0, len)
> +#define SUSPEND_BLOCKER_IOCTL_BLOCK		_IO('s', 1)
> +#define SUSPEND_BLOCKER_IOCTL_UNBLOCK		_IO('s', 2)
> +
> +#endif
> diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
> index 55a06a1..fe5a2f2 100644
> --- a/kernel/power/Kconfig
> +++ b/kernel/power/Kconfig
> @@ -146,6 +146,15 @@ config OPPORTUNISTIC_SUSPEND
>  	  determines the sleep state the system will be put into when there are
>  	  no active suspend blockers.
>  
> +config USER_SUSPEND_BLOCKERS
> +	bool "Userspace suspend blockers"
> +	depends on OPPORTUNISTIC_SUSPEND
> +	default y
> +	---help---
> +	  User-space suspend block api. Creates a misc device with ioctls
> +	  to create, block and unblock a suspend_blocker. The suspend_blocker
> +	  will be deleted when the device is closed.
> +
>  config HIBERNATION_NVS
>  	bool
>  
> diff --git a/kernel/power/Makefile b/kernel/power/Makefile
> index ee5276d..78f703b 100644
> --- a/kernel/power/Makefile
> +++ b/kernel/power/Makefile
> @@ -8,6 +8,7 @@ obj-$(CONFIG_PM_SLEEP)		+= console.o
>  obj-$(CONFIG_FREEZER)		+= process.o
>  obj-$(CONFIG_SUSPEND)		+= suspend.o
>  obj-$(CONFIG_OPPORTUNISTIC_SUSPEND)	+= suspend_blocker.o
> +obj-$(CONFIG_USER_SUSPEND_BLOCKERS)	+= user_suspend_blocker.o
>  obj-$(CONFIG_PM_TEST_SUSPEND)	+= suspend_test.o
>  obj-$(CONFIG_HIBERNATION)	+= hibernate.o snapshot.o swap.o user.o
>  obj-$(CONFIG_HIBERNATION_NVS)	+= hibernate_nvs.o
> diff --git a/kernel/power/user_suspend_blocker.c b/kernel/power/user_suspend_blocker.c
> new file mode 100644
> index 0000000..dc1d06f
> --- /dev/null
> +++ b/kernel/power/user_suspend_blocker.c
> @@ -0,0 +1,128 @@
> +/* kernel/power/user_suspend_block.c
> + *
> + * Copyright (C) 2009-2010 Google, Inc.
> + *
> + * This software is licensed under the terms of the GNU General Public
> + * License version 2, as published by the Free Software Foundation, and
> + * may be copied, distributed, and modified under those terms.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + */
> +
> +#include <linux/fs.h>
> +#include <linux/miscdevice.h>
> +#include <linux/module.h>
> +#include <linux/uaccess.h>
> +#include <linux/slab.h>
> +#include <linux/suspend_blocker.h>
> +#include <linux/suspend_block_dev.h>
> +
> +enum {
> +	DEBUG_FAILURE	= BIT(0),
> +};
> +static int debug_mask = DEBUG_FAILURE;
> +module_param_named(debug_mask, debug_mask, int, S_IRUGO | S_IWUSR | S_IWGRP);
> +
> +static DEFINE_MUTEX(ioctl_lock);
> +
> +struct user_suspend_blocker {
> +	struct suspend_blocker	blocker;
> +	char			name[0];
> +};
> +
> +static int create_user_suspend_blocker(struct file *file, void __user *name,
> +				 size_t name_len)
> +{
> +	struct user_suspend_blocker *bl;
> +	if (file->private_data)
> +		return -EBUSY;
> +	if (name_len > NAME_MAX)
> +		return -ENAMETOOLONG;
> +	bl = kzalloc(sizeof(*bl) + name_len + 1, GFP_KERNEL);
> +	if (!bl)
> +		return -ENOMEM;
> +	if (copy_from_user(bl->name, name, name_len))
> +		goto err_fault;
> +	suspend_blocker_init(&bl->blocker, bl->name);
> +	file->private_data = bl;

Hmm.  It doesn't seem to be possible to create two different suspend blockers
using the same file handle.  So, what exactly is a process supposed to do to
use two suspend blockers at the same time?

Rafael
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