[PATCH 10/15] tracing: Introduce kho serialization

[Alexander Graf]

We want to be able to transfer ftrace state from one kernel to the next.
To start off with, let's establish all the boiler plate to get a write
hook when KHO wants to serialize and fill out basic data.

Follow-up patches will fill in serialization of ring buffers and events.

Signed-off-by: Alexander Graf <g...@amazon.com>
---
 kernel/trace/trace.c | 52 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 7700ca1be2a5..3e7f61cf773e 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -32,6 +32,7 @@
 #include <linux/percpu.h>
 #include <linux/splice.h>
 #include <linux/kdebug.h>
+#include <linux/kexec.h>
 #include <linux/string.h>
 #include <linux/mount.h>
 #include <linux/rwsem.h>
@@ -866,6 +867,10 @@ static struct tracer               *trace_types 
__read_mostly;
  */
 DEFINE_MUTEX(trace_types_lock);
 
+#ifdef CONFIG_FTRACE_KHO
+static bool trace_in_kho;
+#endif
+
 /*
  * serialize the access of the ring buffer
  *
@@ -10591,12 +10596,59 @@ void __init early_trace_init(void)
        init_events();
 }
 
+#ifdef CONFIG_FTRACE_KHO
+static int trace_kho_notifier(struct notifier_block *self,
+                             unsigned long cmd,
+                             void *v)
+{
+       const char compatible[] = "ftrace-v1";
+       void *fdt = v;
+       int err = 0;
+
+       switch (cmd) {
+       case KEXEC_KHO_ABORT:
+               if (trace_in_kho)
+                       mutex_unlock(&trace_types_lock);
+               trace_in_kho = false;
+               return NOTIFY_DONE;
+       case KEXEC_KHO_DUMP:
+               /* Handled below */
+               break;
+       default:
+               return NOTIFY_BAD;
+       }
+
+       if (unlikely(tracing_disabled))
+               return NOTIFY_DONE;
+
+       err |= fdt_begin_node(fdt, "ftrace");
+       err |= fdt_property(fdt, "compatible", compatible, sizeof(compatible));
+       err |= fdt_end_node(fdt);
+
+       if (!err) {
+               /* Hold all future allocations */
+               mutex_lock(&trace_types_lock);
+               trace_in_kho = true;
+       }
+
+       return err ? NOTIFY_BAD : NOTIFY_DONE;
+}
+
+static struct notifier_block trace_kho_nb = {
+       .notifier_call = trace_kho_notifier,
+};
+#endif
+
 void __init trace_init(void)
 {
        trace_event_init();
 
        if (boot_instance_index)
                enable_instances();
+
+#ifdef CONFIG_FTRACE_KHO
+       register_kho_notifier(&trace_kho_nb);
+#endif
 }
 
 __init static void clear_boot_tracer(void)
-- 
2.40.1




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