Linux Kernel Markers: support multiple probes

RCU style multiple probes support for the Linux Kernel Markers.  Common case
(one probe) is still fast and does not require dynamic allocation or a
supplementary pointer dereference on the fast path.

- Move preempt disable from the marker site to the callback.

Since we now have an internal callback, move the preempt disable/enable to the
callback instead of the marker site.

Since the callback change is done asynchronously (passing from a handler that
supports arguments to a handler that does not setup the arguments is no
arguments are passed), we can safely update it even if it is outside the
preempt disable section.

- Move probe arm to probe connection. Now, a connected probe is automatically
  armed.

Remove MARK_MAX_FORMAT_LEN, unused.

This patch modifies the Linux Kernel Markers API : it removes the probe
"arm/disarm" and changes the probe function prototype : it now expects a
va_list * instead of a "...".

If we want to have more than one probe connected to a marker at a given
time (LTTng, or blktrace, ssytemtap) then we need this patch. Without it,
connecting a second probe handler to a marker will fail.

It allow us, for instance, to do interesting combinations :

Do standard tracing with LTTng and, eventually, to compute statistics
with SystemTAP, or to have a special trigger on an event that would call
a systemtap script which would stop flight recorder tracing.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Mike Mason <mmlnx@us.ibm.com>
Cc: Dipankar Sarma <dipankar@in.ibm.com>
Cc: David Smith <dsmith@redhat.com>
Cc: "Paul E. McKenney" <paulmck@us.ibm.com>
Cc: "Frank Ch. Eigler" <fche@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 11 insertions, 20 deletions

diff --git a/arch/powerpc/platforms/cell/spufs/sputrace.c b/arch/powerpc/platforms/cell/spufs/sputrace.c
index 2b1953f6f12e..01974f7776e1 100644
--- a/arch/powerpc/platforms/cell/spufs/sputrace.c
+++ b/arch/powerpc/platforms/cell/spufs/sputrace.c
@@ -146,34 +146,28 @@ static void sputrace_log_item(const char *name, struct spu_context *ctx,
         wake_up(&sputrace_wait);
 }
 
-static void spu_context_event(const struct marker *mdata,
-                void *private, const char *format, ...)
+static void spu_context_event(void *probe_private, void *call_data,
+                const char *format, va_list *args)
 {
-        struct spu_probe *p = mdata->private;
-        va_list ap;
+        struct spu_probe *p = probe_private;
         struct spu_context *ctx;
         struct spu *spu;
 
-        va_start(ap, format);
-        ctx = va_arg(ap, struct spu_context *);
-        spu = va_arg(ap, struct spu *);
+        ctx = va_arg(*args, struct spu_context *);
+        spu = va_arg(*args, struct spu *);
 
         sputrace_log_item(p->name, ctx, spu);
-        va_end(ap);
 }
 
-static void spu_context_nospu_event(const struct marker *mdata,
-                void *private, const char *format, ...)
+static void spu_context_nospu_event(void *probe_private, void *call_data,
+                const char *format, va_list *args)
 {
-        struct spu_probe *p = mdata->private;
-        va_list ap;
+        struct spu_probe *p = probe_private;
         struct spu_context *ctx;
 
-        va_start(ap, format);
-        ctx = va_arg(ap, struct spu_context *);
+        ctx = va_arg(*args, struct spu_context *);
 
         sputrace_log_item(p->name, ctx, NULL);
-        va_end(ap);
 }
 
 struct spu_probe spu_probes[] = {
@@ -219,10 +213,6 @@ static int __init sputrace_init(void)
                 if (error)
                         printk(KERN_INFO "Unable to register probe %s\n",
                                         p->name);
-
-                error = marker_arm(p->name);
-                if (error)
-                        printk(KERN_INFO "Unable to arm probe %s\n", p->name);
         }
 
         return 0;
@@ -238,7 +228,8 @@ static void __exit sputrace_exit(void)
         int i;
 
         for (i = 0; i < ARRAY_SIZE(spu_probes); i++)
-                marker_probe_unregister(spu_probes[i].name);
+                marker_probe_unregister(spu_probes[i].name,
+                        spu_probes[i].probe_func, &spu_probes[i]);
 
         remove_proc_entry("sputrace", NULL);
         kfree(sputrace_log);