Re: [PATCH v7 14/28] tracing: Add a trace remote module for testing

[Vincent Donnefort <vdonnefort@google.com>]

On Thu, Oct 16, 2025 at 05:11:55PM -0400, Steven Rostedt wrote:
> On Thu, 16 Oct 2025 17:06:45 -0400
> Steven Rostedt <rostedt@goodmis.org> wrote:
> 
> > On Fri,  3 Oct 2025 14:38:11 +0100
> > Vincent Donnefort <vdonnefort@google.com> wrote:
> > 
> > > diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> > > index 918afcc1fcaf..52131d89993c 100644
> > > --- a/kernel/trace/Kconfig
> > > +++ b/kernel/trace/Kconfig
> > > @@ -1244,4 +1244,12 @@ config TRACE_REMOTE
> > >  config SIMPLE_RING_BUFFER
> > >  	bool
> > >  
> > > +config TRACE_REMOTE_TEST
> > > +	tristate "Test module for remote tracing"
> > > +	select TRACE_REMOTE
> > > +	select SIMPLE_RING_BUFFER
> > > +	help
> > > +	  This trace remote includes a ring-buffer writer implementation using
> > > +	  "simple_ring_buffer". This is solely intending for testing.
> > > +  
> > 
> > Nit, this should go up a few places so that it's with the other "test module" selections.
> 
> And when I tried to build it, I hit this:
> 
>   GEN     .vmlinux.objs
>   MODPOST Module.symvers
> ERROR: modpost: "simple_ring_buffer_reserve" [kernel/trace/remote_test.ko] undefined!
> ERROR: modpost: "simple_ring_buffer_commit" [kernel/trace/remote_test.ko] undefined!
> ERROR: modpost: "simple_ring_buffer_unload" [kernel/trace/remote_test.ko] undefined!
> ERROR: modpost: "trace_remote_free_buffer" [kernel/trace/remote_test.ko] undefined!
> ERROR: modpost: "trace_remote_alloc_buffer" [kernel/trace/remote_test.ko] undefined!
> ERROR: modpost: "simple_ring_buffer_init" [kernel/trace/remote_test.ko] undefined!
> ERROR: modpost: "trace_remote_register" [kernel/trace/remote_test.ko] undefined!
> ERROR: modpost: "simple_ring_buffer_reset" [kernel/trace/remote_test.ko] undefined!
> ERROR: modpost: "simple_ring_buffer_swap_reader_page" [kernel/trace/remote_test.ko] undefined!
> ERROR: modpost: "simple_ring_buffer_enable_tracing" [kernel/trace/remote_test.ko] undefined!
> WARNING: modpost: suppressed 1 unresolved symbol warnings because there were too many)
> make[3]: *** [/work/git/linux-trace.git/scripts/Makefile.modpost:147: Module.symvers] Error 1
> make[2]: *** [/work/git/linux-trace.git/Makefile:1960: modpost] Error 2
> make[1]: *** [/work/git/linux-trace.git/Makefile:248: __sub-make] Error 2
> make[1]: Leaving directory '/work/build/nobackup/debiantesting-x86-64'
> make: *** [Makefile:248: __sub-make] Error 2

And of course, I forgot to check CONFIG_REMOTE_TEST=M ...

The following snippet should do.

Do you want a v8 now (and with your previous comment) or shall I wait a bit more?

--

diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
index 0c023941a316..aa305be834f9 100644
--- a/fs/tracefs/inode.c
+++ b/fs/tracefs/inode.c
@@ -665,6 +665,7 @@ struct dentry *tracefs_create_file(const char *name, umode_t mode,
        fsnotify_create(d_inode(dentry->d_parent), dentry);
        return tracefs_end_creating(dentry);
 }
+EXPORT_SYMBOL_GPL(tracefs_create_file);
 
 static struct dentry *__create_dir(const char *name, struct dentry *parent,
                                   const struct inode_operations *ops)
diff --git a/kernel/trace/simple_ring_buffer.c b/kernel/trace/simple_ring_buffer.c
index c2ec6017c37c..02303161aab7 100644
--- a/kernel/trace/simple_ring_buffer.c
+++ b/kernel/trace/simple_ring_buffer.c
@@ -162,6 +162,7 @@ int simple_ring_buffer_swap_reader_page(struct simple_rb_per_cpu *cpu_buffer)
 
        return 0;
 }
+EXPORT_SYMBOL_GPL(simple_ring_buffer_swap_reader_page);
 
 static struct simple_buffer_page *simple_rb_move_tail(struct simple_rb_per_cpu *cpu_buffer)
 {
@@ -267,6 +268,7 @@ void *simple_ring_buffer_reserve(struct simple_rb_per_cpu *cpu_buffer, unsigned
 
        return &rb_event->array[1];
 }
+EXPORT_SYMBOL_GPL(simple_ring_buffer_reserve);
 
 void simple_ring_buffer_commit(struct simple_rb_per_cpu *cpu_buffer)
 {
@@ -280,6 +282,7 @@ void simple_ring_buffer_commit(struct simple_rb_per_cpu *cpu_buffer)
         */
        smp_store_release(&cpu_buffer->status, SIMPLE_RB_READY);
 }
+EXPORT_SYMBOL_GPL(simple_ring_buffer_commit);
 
 static u32 simple_rb_enable_tracing(struct simple_rb_per_cpu *cpu_buffer, bool enable)
 {
@@ -337,6 +340,7 @@ int simple_ring_buffer_reset(struct simple_rb_per_cpu *cpu_buffer)
 
        return 0;
 }
+EXPORT_SYMBOL_GPL(simple_ring_buffer_reset);
 
 int __simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer,
                              struct simple_buffer_page *bpages,
@@ -427,6 +431,7 @@ int simple_ring_buffer_init(struct simple_rb_per_cpu *cpu_buffer, struct simple_
 {
        return __simple_ring_buffer_init(cpu_buffer, bpages, desc, __load_page, __unload_page);
 }
+EXPORT_SYMBOL_GPL(simple_ring_buffer_init);
 
 void __simple_ring_buffer_unload(struct simple_rb_per_cpu *cpu_buffer,
                                 void (*unload_page)(void *))
@@ -449,6 +454,7 @@ void simple_ring_buffer_unload(struct simple_rb_per_cpu *cpu_buffer)
 {
        return __simple_ring_buffer_unload(cpu_buffer, __unload_page);
 }
+EXPORT_SYMBOL_GPL(simple_ring_buffer_unload);
 
 int simple_ring_buffer_enable_tracing(struct simple_rb_per_cpu *cpu_buffer, bool enable)
 {
@@ -459,3 +465,4 @@ int simple_ring_buffer_enable_tracing(struct simple_rb_per_cpu *cpu_buffer, bool
 
        return 0;
 }
+EXPORT_SYMBOL_GPL(simple_ring_buffer_enable_tracing);
diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c
index dc6bc387ebca..e54cc3e75dc5 100644
--- a/kernel/trace/trace_remote.c
+++ b/kernel/trace/trace_remote.c
@@ -895,6 +895,7 @@ int trace_remote_register(const char *name, struct trace_remote_callbacks *cbs,
 
        return ret;
 }
+EXPORT_SYMBOL_GPL(trace_remote_register);
 
 void trace_remote_free_buffer(struct trace_buffer_desc *desc)
 {
@@ -910,6 +911,7 @@ void trace_remote_free_buffer(struct trace_buffer_desc *desc)
                        free_page(rb_desc->page_va[id]);
        }
 }
+EXPORT_SYMBOL_GPL(trace_remote_free_buffer);
 
 int trace_remote_alloc_buffer(struct trace_buffer_desc *desc, size_t desc_size, size_t buffer_size,
                              const struct cpumask *cpumask)
@@ -960,6 +962,7 @@ int trace_remote_alloc_buffer(struct trace_buffer_desc *desc, size_t desc_size,
        trace_remote_free_buffer(desc);
        return ret;
 }
+EXPORT_SYMBOL_GPL(trace_remote_alloc_buffer);
 
 static int
 trace_remote_enable_event(struct trace_remote *remote, struct remote_event *evt, bool enable)