Commit 950032ff authored by Steven Rostedt (Google)'s avatar Steven Rostedt (Google)
Browse files

ring-buffer: Add output of ring buffer meta page 

Add a buffer_meta per-cpu file for the trace instance that is mapped to
boot memory. This shows the current meta-data and can be used by user
space tools to record off the current mappings to help reconstruct the
ring buffer after a reboot.

It does not expose any virtual addresses, just indexes into the sub-buffer
pages.

Link: https://lkml.kernel.org/r/20240612232025.854471446@goodmis.org



Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Vincent Donnefort <vdonnefort@google.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vineeth Pillai <vineeth@bitbyteword.org>
Cc: Youssef Esmat <youssefesmat@google.com>
Cc: Beau Belgrave <beaub@linux.microsoft.com>
Cc: Alexander Graf <graf@amazon.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Ross Zwisler <zwisler@google.com>
Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 2124de79

kernel/trace/ring_buffer.c

+77 −0
Original line number Diff line number Diff line
@@ -32,6 +32,8 @@ 
#include <asm/local64.h>

#include <asm/local.h>



#include "trace.h"



/*

 * The "absolute" timestamp in the buffer is only 59 bits.

 * If a clock has the 5 MSBs set, it needs to be saved and
@@ -1647,6 +1649,81 @@ static void rb_range_meta_init(struct trace_buffer *buffer, int nr_pages) 
	}

}



static void *rbm_start(struct seq_file *m, loff_t *pos)

{

	struct ring_buffer_per_cpu *cpu_buffer = m->private;

	struct ring_buffer_meta *meta = cpu_buffer->ring_meta;

	unsigned long val;



	if (!meta)

		return NULL;



	if (*pos > meta->nr_subbufs)

		return NULL;



	val = *pos;

	val++;



	return (void *)val;

}



static void *rbm_next(struct seq_file *m, void *v, loff_t *pos)

{

	(*pos)++;



	return rbm_start(m, pos);

}



static int rb_meta_subbuf_idx(struct ring_buffer_meta *meta, void *subbuf);



static int rbm_show(struct seq_file *m, void *v)

{

	struct ring_buffer_per_cpu *cpu_buffer = m->private;

	struct ring_buffer_meta *meta = cpu_buffer->ring_meta;

	unsigned long val = (unsigned long)v;



	if (val == 1) {

		seq_printf(m, "head_buffer:   %d\n",

			   rb_meta_subbuf_idx(meta, (void *)meta->head_buffer));

		seq_printf(m, "commit_buffer: %d\n",

			   rb_meta_subbuf_idx(meta, (void *)meta->commit_buffer));

		seq_printf(m, "subbuf_size:   %d\n", meta->subbuf_size);

		seq_printf(m, "nr_subbufs:    %d\n", meta->nr_subbufs);

		return 0;

	}



	val -= 2;

	seq_printf(m, "buffer[%ld]:    %d\n", val, meta->buffers[val]);



	return 0;

}



static void rbm_stop(struct seq_file *m, void *p)

{

}



static const struct seq_operations rb_meta_seq_ops = {

	.start		= rbm_start,

	.next		= rbm_next,

	.show		= rbm_show,

	.stop		= rbm_stop,

};



int ring_buffer_meta_seq_init(struct file *file, struct trace_buffer *buffer, int cpu)

{

	struct seq_file *m;

	int ret;



	ret = seq_open(file, &rb_meta_seq_ops);

	if (ret)

		return ret;



	m = file->private_data;

	m->private = buffer->buffers[cpu];



	return 0;

}



static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,

		long nr_pages, struct list_head *pages)

{

kernel/trace/trace.c

+28 −2
Original line number Diff line number Diff line
@@ -5018,7 +5018,7 @@ static int show_traces_open(struct inode *inode, struct file *file) 
	return 0;

}



static int show_traces_release(struct inode *inode, struct file *file)

static int tracing_seq_release(struct inode *inode, struct file *file)

{

	struct trace_array *tr = inode->i_private;
@@ -5059,7 +5059,7 @@ static const struct file_operations show_traces_fops = { 
	.open		= show_traces_open,

	.read		= seq_read,

	.llseek		= seq_lseek,

	.release	= show_traces_release,

	.release	= tracing_seq_release,

};



static ssize_t
@@ -6860,6 +6860,22 @@ tracing_total_entries_read(struct file *filp, char __user *ubuf, 
	return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);

}



static int tracing_buffer_meta_open(struct inode *inode, struct file *filp)

{

	struct trace_array *tr = inode->i_private;

	int cpu = tracing_get_cpu(inode);

	int ret;



	ret = tracing_check_open_get_tr(tr);

	if (ret)

		return ret;



	ret = ring_buffer_meta_seq_init(filp, tr->array_buffer.buffer, cpu);

	if (ret < 0)

		__trace_array_put(tr);

	return ret;

}



static ssize_t

tracing_free_buffer_write(struct file *filp, const char __user *ubuf,

			  size_t cnt, loff_t *ppos)
@@ -7436,6 +7452,13 @@ static const struct file_operations tracing_entries_fops = { 
	.release	= tracing_release_generic_tr,

};



static const struct file_operations tracing_buffer_meta_fops = {

	.open		= tracing_buffer_meta_open,

	.read		= seq_read,

	.llseek		= seq_lseek,

	.release	= tracing_seq_release,

};



static const struct file_operations tracing_total_entries_fops = {

	.open		= tracing_open_generic_tr,

	.read		= tracing_total_entries_read,
@@ -8668,6 +8691,9 @@ tracing_init_tracefs_percpu(struct trace_array *tr, long cpu) 
	trace_create_cpu_file("buffer_size_kb", TRACE_MODE_READ, d_cpu,

				tr, cpu, &tracing_entries_fops);



	if (tr->range_addr_start)

		trace_create_cpu_file("buffer_meta", TRACE_MODE_READ, d_cpu,

				      tr, cpu, &tracing_buffer_meta_fops);

#ifdef CONFIG_TRACER_SNAPSHOT

	if (!tr->range_addr_start) {

		trace_create_cpu_file("snapshot", TRACE_MODE_WRITE, d_cpu,

kernel/trace/trace.h

+2 −0
Original line number Diff line number Diff line
@@ -645,6 +645,8 @@ trace_buffer_lock_reserve(struct trace_buffer *buffer, 
			  unsigned long len,

			  unsigned int trace_ctx);



int ring_buffer_meta_seq_init(struct file *file, struct trace_buffer *buffer, int cpu);



struct trace_entry *tracing_get_trace_entry(struct trace_array *tr,

						struct trace_array_cpu *data);