linux-kernel - [RFD PATCH 2/4] cpu: sysfs interface for hotplugging bunch of CPUs.

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Date:	Tue, 16 Jun 2009 11:08:49 +0530
From:	Gautham R Shenoy <ego@...ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Balbir Singh <balbir@...ibm.com>,
	Rusty Russel <rusty@...tcorp.com.au>,
	Paul E McKenney <paulmck@...ibm.com>,
	Nathan Lynch <ntl@...ox.com>, Ingo Molnar <mingo@...e.hu>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Shoahua Li <shaohua.li@...ux.com>
Subject: [RFD PATCH 2/4] cpu: sysfs interface for hotplugging bunch of CPUs.

The user can currently view the online and offline CPUs in the system through
the sysfs files named "online" and "offline" respectively which
are present in the directory /sys/devices/system/cpu/. These files currently
have 0444 permissions.

For the purpose of evacuation of a bunch of CPUs, we propose to extend this
same interface and make it 0644, by which the user can use the same interface
to bring a bunch of CPUs online or take a bunch of CPUs offline.

To do this, the user is required to echo the cpu-list which is expected to be
hotplugged.

Eg:

echo 2,3 > /sys/devices/system/cpu/offline #Offlines CPUs 2 and 3
echo 4 > /sys/devices/sytem/cpu/offline    #Offlines CPU 4
echo 2-4 > /sys/devices/system/cpu/online  #Onlines CPU 2,3,4

This patch changes the permissions of these sysfs files from 0444 to 0644.
It provides a dummy store function, which currently parses the input
provided by the user and copies them to another debug cpumask structure,
which can be accessed using the sysfs interfaces:
	/sys/devices/system/cpu/debug_offline
and
	/sys/devices/system/cpu/debug_online

Thus on performing a
	echo 2,3 > /sys/devices/system/cpu/offline
the operation
	cat /sys/devices/system/cpu/debug_offline
should yield
	2-3
as the result.

Signed-off-by: Gautham R Shenoy <ego@...ibm.com>
---
 drivers/base/cpu.c |   72 ++++++++++++++++++++++++++++++++++++++++++++++++----
 1 files changed, 67 insertions(+), 5 deletions(-)

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index e62a4cc..7a15e7b 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -116,18 +116,54 @@ static ssize_t print_cpus_map(char *buf, const struct cpumask *map)
 	return n;
 }
 
-#define	print_cpus_func(type) \
+#define show_cpus_func(type)						\
 static ssize_t print_cpus_##type(struct sysdev_class *class, char *buf)	\
 {									\
 	return print_cpus_map(buf, cpu_##type##_mask);			\
-}									\
-static struct sysdev_class_attribute attr_##type##_map = 		\
+}
+
+#define print_cpus_func(type)						\
+show_cpus_func(type);							\
+static struct sysdev_class_attribute attr_##type##_map =		\
 	_SYSDEV_CLASS_ATTR(type, 0444, print_cpus_##type, NULL)
 
-print_cpus_func(online);
 print_cpus_func(possible);
 print_cpus_func(present);
 
+static struct cpumask debug_offline_mask_data;
+static struct cpumask debug_online_mask_data;
+static struct cpumask *cpu_debug_offline_mask = &debug_offline_mask_data;
+static struct cpumask *cpu_debug_online_mask = &debug_online_mask_data;
+print_cpus_func(debug_offline);
+print_cpus_func(debug_online);
+
+show_cpus_func(online);
+static ssize_t store_cpus_online(struct sysdev_class *dev_class,
+					const char *buf, size_t count)
+{
+	ssize_t ret = count;
+	cpumask_var_t store_cpus_online_mask;
+
+	if (!alloc_cpumask_var(&store_cpus_online_mask, GFP_KERNEL))
+		return count;
+
+	ret = cpulist_parse(buf, store_cpus_online_mask);
+
+	if (ret < 0)
+		goto out;
+
+	cpumask_copy(cpu_debug_online_mask, store_cpus_online_mask);
+
+out:
+	free_cpumask_var(store_cpus_online_mask);
+	if (ret >= 0)
+		ret = count;
+	return ret;
+}
+static struct sysdev_class_attribute attr_online_map =
+	_SYSDEV_CLASS_ATTR(online, 0644, print_cpus_online,
+						store_cpus_online);
+
 /*
  * Print values for NR_CPUS and offlined cpus
  */
@@ -168,7 +204,31 @@ static ssize_t print_cpus_offline(struct sysdev_class *class, char *buf)
 	n += snprintf(&buf[n], len - n, "\n");
 	return n;
 }
-static SYSDEV_CLASS_ATTR(offline, 0444, print_cpus_offline, NULL);
+
+static ssize_t store_cpus_offline(struct sysdev_class *dev_class,
+					const char *buf, size_t count)
+{
+	ssize_t ret = count;
+	cpumask_var_t store_cpus_offline_mask;
+
+	if (!alloc_cpumask_var(&store_cpus_offline_mask, GFP_KERNEL))
+		return count;
+
+	ret = cpulist_parse(buf, store_cpus_offline_mask);
+
+	if (ret < 0)
+		goto out;
+
+	cpumask_copy(cpu_debug_offline_mask, store_cpus_offline_mask);
+
+out:
+	free_cpumask_var(store_cpus_offline_mask);
+	if (ret >= 0)
+		ret = count;
+	return ret;
+}
+static SYSDEV_CLASS_ATTR(offline, 0644, print_cpus_offline,
+						store_cpus_offline);
 
 static struct sysdev_class_attribute *cpu_state_attr[] = {
 	&attr_online_map,
@@ -176,6 +236,8 @@ static struct sysdev_class_attribute *cpu_state_attr[] = {
 	&attr_present_map,
 	&attr_kernel_max,
 	&attr_offline,
+	&attr_debug_online_map,
+	&attr_debug_offline_map,
 };
 
 static int cpu_states_init(void)

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