[PATCH] kdump: Add udev events for memory online/offline

[Michael Holzheu <holzheu@linux.vnet.ibm.com>]

From: Michael Holzheu <holzheu@linux.vnet.ibm.com>

Currently no udev events for memory hotplug "online" and "offline" are
generated:

# udevadm monitor
# echo offline > /sys/devices/system/memory/memory4/state
==> No event

When kdump is loaded, kexec detects the current memory configuration and
stores it in the pre-allocated ELF core header. Therefore, for kdump it is
necessary to reload the kdump kernel with kexec when the memory
configuration changes (e.g. for online/offline hotplug memory).

In order to do this automatically, udev rules should be used. This kernel
patch adds udev events for "online" and "offline". Together with this kernel
patch, the following udev rules for online/offline have to be added to
"/etc/udev/rules.d/98-kexec.rules":

SUBSYSTEM=="memory", ACTION=="online", PROGRAM="/etc/init.d/kdump restart"
SUBSYSTEM=="memory", ACTION=="offline", PROGRAM="/etc/init.d/kdump restart"

Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
---
 drivers/base/memory.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -310,11 +310,15 @@ store_mem_state(struct sys_device *dev,
 
 	mem = container_of(dev, struct memory_block, sysdev);
 
-	if (!strncmp(buf, "online", min((int)count, 6)))
+	if (!strncmp(buf, "online", min((int)count, 6))) {
 		ret = memory_block_change_state(mem, MEM_ONLINE, MEM_OFFLINE);
-	else if(!strncmp(buf, "offline", min((int)count, 7)))
+		if (ret == 0)
+			kobject_uevent(&dev->kobj, KOBJ_ONLINE);
+	} else if (!strncmp(buf, "offline", min((int)count, 7))) {
 		ret = memory_block_change_state(mem, MEM_OFFLINE, MEM_ONLINE);
-
+		if (ret == 0)
+			kobject_uevent(&dev->kobj, KOBJ_OFFLINE);
+	}
 	if (ret)
 		return ret;
 	return count;