[PATCH 2/8] PM: suspend_block: Add driver to access suspend blockers from user-space

[Arve HjÃnnevÃg]

Add a misc device, "suspend_blocker", that allows user-space processes
to block automatic suspend.

Opening this device creates a suspend blocker that can be used by the
opener to prevent automatic suspend from occurring.  There are ioctls
provided for blocking and unblocking suspend and for giving the
suspend blocker a meaningful name.  Closing the device special file
causes the suspend blocker to be destroyed.

For example, when select or poll indicates that input event are
available, this interface can be used by user space to block suspend
before it reads those events. This allows the input driver to release
its suspend blocker as soon as the event queue is empty. If user space
could not use a suspend blocker here the input driver would need to
delay the release of its suspend blocker until it knows (or assumes)
that user space has finished processing the events.

By careful use of suspend blockers in drivers and user space system
code, one can arrange for the system to stay awake for extremely short
periods of time in reaction to events, rapidly returning to a fully
suspended state.

Signed-off-by: Arve HjÃnnevÃg <arve@xxxxxxxxxxx>
---
 Documentation/ioctl/ioctl-number.txt          |    3 +-
 Documentation/power/opportunistic-suspend.txt |   27 +++++
 include/linux/suspend_ioctls.h                |    4 +
 kernel/power/Kconfig                          |    7 ++
 kernel/power/Makefile                         |    1 +
 kernel/power/user_suspend_blocker.c           |  143 +++++++++++++++++++++++++
 6 files changed, 184 insertions(+), 1 deletions(-)
 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 4bee7bc..93f4c24 100644
--- a/Documentation/power/opportunistic-suspend.txt
+++ b/Documentation/power/opportunistic-suspend.txt
@@ -127,3 +127,30 @@ if (list_empty(&state->pending_work))
 	suspend_unblock(&state->suspend_blocker);
 else
 	suspend_block(&state->suspend_blocker);
+
+User space API
+==============
+
+To create a suspend blocker from user space, open the suspend_blocker special
+device file:
+
+    fd = open("/dev/suspend_blocker", O_RDWR | O_CLOEXEC);
+
+then optionally call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_SET_NAME(strlen(name)), name);
+
+To activate the suspend blocker call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_BLOCK);
+
+To deactivate it call:
+
+    ioctl(fd, SUSPEND_BLOCKER_IOCTL_UNBLOCK);
+
+To destroy the suspend blocker, close the device:
+
+    close(fd);
+
+If the first ioctl called is not SUSPEND_BLOCKER_IOCTL_SET_NAME the suspend
+blocker will get the default name "(userspace)".
diff --git a/include/linux/suspend_ioctls.h b/include/linux/suspend_ioctls.h
index 0b30382..b95a6b2 100644
--- a/include/linux/suspend_ioctls.h
+++ b/include/linux/suspend_ioctls.h
@@ -30,4 +30,8 @@ struct resume_swap_area {
 #define SNAPSHOT_ALLOC_SWAP_PAGE	_IOR(SNAPSHOT_IOC_MAGIC, 20, __kernel_loff_t)
 #define SNAPSHOT_IOC_MAXNR	20
 
+#define SUSPEND_BLOCKER_IOCTL_SET_NAME(len)	_IOC(_IOC_WRITE, 's', 0, len)
+#define SUSPEND_BLOCKER_IOCTL_BLOCK		_IO('s', 1)
+#define SUSPEND_BLOCKER_IOCTL_UNBLOCK		_IO('s', 2)
+
 #endif /* _LINUX_SUSPEND_IOCTLS_H */
diff --git a/kernel/power/Kconfig b/kernel/power/Kconfig
index 6d11a45..2e665cd 100644
--- a/kernel/power/Kconfig
+++ b/kernel/power/Kconfig
@@ -146,6 +146,13 @@ 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 "User space suspend blockers"
+	depends on OPPORTUNISTIC_SUSPEND
+	---help---
+	  User space suspend blockers API.  Creates a misc device allowing user
+	  space to create, use and destroy suspend blockers.
+
 config HIBERNATION_NVS
 	bool
 
diff --git a/kernel/power/Makefile b/kernel/power/Makefile
index 95d8e6d..2015594 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)	+= opportunistic_suspend.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..d53f939
--- /dev/null
+++ b/kernel/power/user_suspend_blocker.c
@@ -0,0 +1,143 @@
+/*
+ * kernel/power/user_suspend_blocker.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.h>
+#include <linux/suspend_ioctls.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);
+
+#define USER_SUSPEND_BLOCKER_NAME_LEN 31
+
+struct user_suspend_blocker {
+	struct suspend_blocker	blocker;
+	char			name[USER_SUSPEND_BLOCKER_NAME_LEN + 1];
+	bool			registered;
+};
+
+static int user_suspend_blocker_open(struct inode *inode, struct file *filp)
+{
+	struct user_suspend_blocker *blocker;
+
+	blocker = kzalloc(sizeof(*blocker), GFP_KERNEL);
+	if (!blocker)
+		return -ENOMEM;
+
+	nonseekable_open(inode, filp);
+	strcpy(blocker->name, "(userspace)");
+	blocker->blocker.name = blocker->name;
+	filp->private_data = blocker;
+
+	return 0;
+}
+
+static int suspend_blocker_set_name(struct user_suspend_blocker *blocker,
+				    void __user *name, size_t name_len)
+{
+	if (blocker->registered)
+		return -EBUSY;
+
+	if (name_len > USER_SUSPEND_BLOCKER_NAME_LEN)
+		name_len = USER_SUSPEND_BLOCKER_NAME_LEN;
+
+	if (copy_from_user(blocker->name, name, name_len))
+		return -EFAULT;
+	blocker->name[name_len] = '\0';
+
+	return 0;
+}
+
+static long user_suspend_blocker_ioctl(struct file *filp, unsigned int cmd,
+					unsigned long _arg)
+{
+	void __user *arg = (void __user *)_arg;
+	struct user_suspend_blocker *blocker = filp->private_data;
+	long ret = 0;
+
+	mutex_lock(&ioctl_lock);
+	if ((cmd & ~IOCSIZE_MASK) == SUSPEND_BLOCKER_IOCTL_SET_NAME(0)) {
+		ret = suspend_blocker_set_name(blocker, arg, _IOC_SIZE(cmd));
+		goto done;
+	}
+	if (!blocker->registered) {
+		suspend_blocker_register(&blocker->blocker);
+		blocker->registered = true;
+	}
+	switch (cmd) {
+	case SUSPEND_BLOCKER_IOCTL_BLOCK:
+		suspend_block(&blocker->blocker);
+		break;
+
+	case SUSPEND_BLOCKER_IOCTL_UNBLOCK:
+		suspend_unblock(&blocker->blocker);
+		break;
+
+	default:
+		ret = -ENOTTY;
+	}
+done:
+	if (ret && (debug_mask & DEBUG_FAILURE))
+		pr_err("user_suspend_blocker_ioctl: cmd %x failed, %ld\n",
+			cmd, ret);
+	mutex_unlock(&ioctl_lock);
+	return ret;
+}
+
+static int user_suspend_blocker_release(struct inode *inode, struct file *filp)
+{
+	struct user_suspend_blocker *blocker = filp->private_data;
+
+	if (blocker->registered)
+		suspend_blocker_unregister(&blocker->blocker);
+	kfree(blocker);
+
+	return 0;
+}
+
+const struct file_operations user_suspend_blocker_fops = {
+	.open = user_suspend_blocker_open,
+	.release = user_suspend_blocker_release,
+	.unlocked_ioctl = user_suspend_blocker_ioctl,
+};
+
+struct miscdevice user_suspend_blocker_device = {
+	.minor = MISC_DYNAMIC_MINOR,
+	.name = "suspend_blocker",
+	.fops = &user_suspend_blocker_fops,
+};
+
+static int __init user_suspend_blocker_init(void)
+{
+	return misc_register(&user_suspend_blocker_device);
+}
+
+static void __exit user_suspend_blocker_exit(void)
+{
+	misc_deregister(&user_suspend_blocker_device);
+}
+
+module_init(user_suspend_blocker_init);
+module_exit(user_suspend_blocker_exit);
-- 
1.6.5.1

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