[PATCH v5 04/25] tracing: Add reset to trace remotes

[Vincent Donnefort]

For standard trace instance, "trace" files allow to do non-consuming
read of the ring-buffers. This is however not applicable to ring-buffer
remotes due to the lack of support in the meta-page. Nonetheless this
file is still useful to reset a ring-buffer so let's add a write-only
version.

Signed-off-by: Vincent Donnefort <vdonnef...@google.com>

diff --git a/include/linux/trace_remote.h b/include/linux/trace_remote.h
index de043a6f2fe0..1aa99da3c96a 100644
--- a/include/linux/trace_remote.h
+++ b/include/linux/trace_remote.h
@@ -11,6 +11,7 @@ struct trace_remote_callbacks {
        void    (*unload_trace_buffer)(struct trace_buffer_desc *desc, void 
*priv);
        int     (*enable_tracing)(bool enable, void *priv);
        int     (*swap_reader_page)(unsigned int cpu, void *priv);
+       int     (*reset)(unsigned int cpu, void *priv);
 };
 
 int trace_remote_register(const char *name, struct trace_remote_callbacks 
*cbs, void *priv);
diff --git a/kernel/trace/trace_remote.c b/kernel/trace/trace_remote.c
index 1a4786b7970c..18b2930186cc 100644
--- a/kernel/trace/trace_remote.c
+++ b/kernel/trace/trace_remote.c
@@ -63,6 +63,7 @@ static int trace_remote_load(struct trace_remote *remote)
        rb_remote->desc = remote->trace_buffer_desc;
        rb_remote->swap_reader_page = remote->cbs->swap_reader_page;
        rb_remote->priv = remote->priv;
+       rb_remote->reset = remote->cbs->reset;
        remote->trace_buffer = ring_buffer_remote(rb_remote);
        if (!remote->trace_buffer) {
                remote->cbs->unload_trace_buffer(remote->trace_buffer_desc, 
remote->priv);
@@ -136,6 +137,21 @@ static int trace_remote_disable_tracing(struct 
trace_remote *remote)
        return 0;
 }
 
+static void trace_remote_reset(struct trace_remote *remote, int cpu)
+{
+       lockdep_assert_held(&remote->lock);
+
+       if (!trace_remote_loaded(remote))
+               return;
+
+       if (cpu == RING_BUFFER_ALL_CPUS)
+               ring_buffer_reset(remote->trace_buffer);
+       else
+               ring_buffer_reset_cpu(remote->trace_buffer, cpu);
+
+       trace_remote_try_unload(remote);
+}
+
 static ssize_t
 tracing_on_write(struct file *filp, const char __user *ubuf, size_t cnt, 
loff_t *ppos)
 {
@@ -370,6 +386,26 @@ static const struct file_operations trace_pipe_fops = {
        .release        = trace_pipe_release,
 };
 
+static ssize_t trace_write(struct file *filp, const char __user *ubuf, size_t 
cnt, loff_t *ppos)
+{
+       struct inode *inode = file_inode(filp);
+       struct trace_remote *remote = inode->i_private;
+       int cpu = RING_BUFFER_ALL_CPUS;
+
+       if (inode->i_cdev)
+               cpu = (long)inode->i_cdev - 1;
+
+       guard(mutex)(&remote->lock);
+
+       trace_remote_reset(remote, cpu);
+
+       return cnt;
+}
+
+static const struct file_operations trace_fops = {
+       .write          = trace_write,
+};
+
 static int trace_remote_init_tracefs(const char *name, struct trace_remote 
*remote)
 {
        struct dentry *remote_d, *percpu_d;
@@ -400,7 +436,9 @@ static int trace_remote_init_tracefs(const char *name, 
struct trace_remote *remo
            !trace_create_file("buffer_size_kb", TRACEFS_MODE_WRITE, remote_d, 
remote,
                               &buffer_size_kb_fops) ||
            !trace_create_file("trace_pipe", TRACEFS_MODE_READ, remote_d, 
remote,
-                              &trace_pipe_fops))
+                              &trace_pipe_fops) ||
+           !trace_create_file("trace", 0200, remote_d, remote,
+                              &trace_fops))
                goto err;
 
        percpu_d = tracefs_create_dir("per_cpu", remote_d);
@@ -422,7 +460,9 @@ static int trace_remote_init_tracefs(const char *name, 
struct trace_remote *remo
                }
 
                if (!trace_create_cpu_file("trace_pipe", TRACEFS_MODE_READ, 
cpu_d, remote, cpu,
-                                          &trace_pipe_fops))
+                                          &trace_pipe_fops) ||
+                   !trace_create_cpu_file("trace", 0200, cpu_d, remote, cpu,
+                                          &trace_fops))
                        goto err;
        }
 
-- 
2.49.0.1101.gccaa498523-goog