[PATCH] Hot-plug CPU Boot Changes

This patch alters the boot sequence to "plug in" each CPU, one at a
time.  You need the patch for each architecture, as well.  The
interface used to be "smp_boot_cpus()", "smp_commence()", and each
arch implemented the "maxcpus" boot arg itself.  With this patch,
it is:
  smp_prepare_cpus(maxcpus): probe for cpus and set up cpu_possible(cpu).
  __cpu_up(cpu): called *after* initcalls, for each cpu where
     cpu_possible(cpu) is true.
  smp_cpus_done(maxcpus): called after every cpu has been brought up

1 files changed, 54 insertions, 0 deletions

diff --git a/kernel/cpu.c b/kernel/cpu.c
new file mode 100644
index 000000000000..b1820a5536d6
--- /dev/null
+++ b/kernel/cpu.c
@@ -0,0 +1,54 @@
+/* CPU control.
+ * (C) 2001 Rusty Russell
+ * This code is licenced under the GPL.
+ */
+#include <linux/proc_fs.h>
+#include <linux/smp.h>
+#include <linux/init.h>
+#include <linux/notifier.h>
+#include <linux/sched.h>
+#include <linux/unistd.h>
+#include <asm/semaphore.h>
+
+/* This protects CPUs going up and down... */
+DECLARE_MUTEX(cpucontrol);
+
+static struct notifier_block *cpu_chain = NULL;
+
+/* Need to know about CPUs going up/down? */
+int register_cpu_notifier(struct notifier_block *nb)
+{
+	return notifier_chain_register(&cpu_chain, nb);
+}
+
+void unregister_cpu_notifier(struct notifier_block *nb)
+{
+	notifier_chain_unregister(&cpu_chain,nb);
+}
+
+int __devinit cpu_up(unsigned int cpu)
+{
+	int ret;
+
+	if ((ret = down_interruptible(&cpucontrol)) != 0) 
+		return ret;
+
+	if (cpu_online(cpu)) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	/* Arch-specific enabling code. */
+	ret = __cpu_up(cpu);
+	if (ret != 0) goto out;
+	if (!cpu_online(cpu))
+		BUG();
+
+	/* Now call notifier in preparation. */
+	printk("CPU %u IS NOW UP!\n", cpu);
+	notifier_call_chain(&cpu_chain, CPU_ONLINE, (void *)cpu);
+
+ out:
+	up(&cpucontrol);
+	return ret;
+}