Re: [PATCH 7/8] tracing: Show module names and addresses of last boot

[Google]

On Wed, 05 Feb 2025 17:50:38 -0500
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> From: Steven Rostedt <rostedt@xxxxxxxxxxx>
> 
> Add the last boot module's names and addresses to the last_boot_info file.
> This only shows the module information from a previous boot. If the buffer
> is started and is recording the current boot, this file still will only
> show "current".
> 
>   # cat instances/boot_mapped/last_boot_info
>   Offset: 10c00000
>   ffffffffc00ca000 usb_serial_simple
>   ffffffffc00ae000 usbserial
>   ffffffffc008b000 bfq

This is just a suggestion, what about using the same format for all
lines? For example,

# cat instances/boot_mapped/last_boot_info
10c00000         [kernel]
ffffffffc00ca000 usb_serial_simple
ffffffffc00ae000 usbserial
ffffffffc008b000 bfq

> 
>   # echo function > instances/boot_mapped/current_tracer
>   # cat instances/boot_mapped/last_boot_info
>   Offset: current

And this one is empty if it is already for the current.
(because last boot information is cleared)

Thank you,

> 
> Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
> ---
>  kernel/trace/trace.c | 103 +++++++++++++++++++++++++++++++++++++------
>  1 file changed, 90 insertions(+), 13 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index a8e5f7ac2193..7b4027804cd4 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -6005,6 +6005,8 @@ struct trace_scratch {
>  	struct trace_mod_entry	entries[];
>  };
>  
> +static DEFINE_MUTEX(scratch_mutex);
> +
>  static int save_mod(struct module *mod, void *data)
>  {
>  	struct trace_array *tr = data;
> @@ -6012,6 +6014,8 @@ static int save_mod(struct module *mod, void *data)
>  	struct trace_mod_entry *entry;
>  	unsigned int size;
>  
> +	guard(mutex)(&scratch_mutex);
> +
>  	tscratch = tr->scratch;
>  	if (!tscratch)
>  		return -1;
> @@ -6882,15 +6886,47 @@ tracing_total_entries_read(struct file *filp, char __user *ubuf,
>  	return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
>  }
>  
> -static ssize_t
> -tracing_last_boot_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t *ppos)
> +#define LAST_BOOT_HEADER ((void *)1)
> +
> +static void *l_next(struct seq_file *m, void *v, loff_t *pos)
>  {
> -	struct trace_array *tr = filp->private_data;
> +	struct trace_array *tr = m->private;
>  	struct trace_scratch *tscratch = tr->scratch;
> -	struct seq_buf seq;
> -	char buf[64];
> +	unsigned int index = *pos;
> +
> +	(*pos)++;
> +
> +	if (*pos == 1)
> +		return LAST_BOOT_HEADER;
> +
> +	/* Only show offsets of the last boot data */
> +	if (!tscratch || !(tr->flags & TRACE_ARRAY_FL_LAST_BOOT))
> +		return NULL;
> +
> +	/* *pos 0 is for the header, 1 is for the first module */
> +	index--;
> +
> +	if (index >= tscratch->nr_entries)
> +		return NULL;
>  
> -	seq_buf_init(&seq, buf, 64);
> +	return &tscratch->entries[index];
> +}
> +
> +static void *l_start(struct seq_file *m, loff_t *pos)
> +{
> +	mutex_lock(&scratch_mutex);
> +
> +	return l_next(m, NULL, pos);
> +}
> +
> +static void l_stop(struct seq_file *m, void *p)
> +{
> +	mutex_unlock(&scratch_mutex);
> +}
> +
> +static void show_last_boot_header(struct seq_file *m, struct trace_array *tr)
> +{
> +	struct trace_scratch *tscratch = tr->scratch;
>  
>  	/*
>  	 * Do not leak KASLR address. This only shows the KASLR address of
> @@ -6900,11 +6936,52 @@ tracing_last_boot_read(struct file *filp, char __user *ubuf, size_t cnt, loff_t
>  	 * should not be the same as the current boot.
>  	 */
>  	if (!tscratch || !(tr->flags & TRACE_ARRAY_FL_LAST_BOOT))
> -		seq_buf_puts(&seq, "Offset: current\n");
> +		seq_puts(m, "Offset: current\n");
>  	else
> -		seq_buf_printf(&seq, "Offset: %lx\n", tscratch->kaslr_addr);
> +		seq_printf(m, "Offset: %lx\n", tscratch->kaslr_addr);
> +}
>  
> -	return simple_read_from_buffer(ubuf, cnt, ppos, buf, seq_buf_used(&seq));
> +static int l_show(struct seq_file *m, void *v)
> +{
> +	struct trace_array *tr = m->private;
> +	struct trace_mod_entry *entry = v;
> +
> +	if (v == LAST_BOOT_HEADER) {
> +		show_last_boot_header(m, tr);
> +		return 0;
> +	}
> +
> +	seq_printf(m, "%lx %s\n", entry->mod_addr, entry->mod_name);
> +	return 0;
> +}
> +
> +static const struct seq_operations last_boot_seq_ops = {
> +	.start		= l_start,
> +	.next		= l_next,
> +	.stop		= l_stop,
> +	.show		= l_show,
> +};
> +
> +static int tracing_last_boot_open(struct inode *inode, struct file *file)
> +{
> +	struct trace_array *tr = inode->i_private;
> +	struct seq_file *m;
> +	int ret;
> +
> +	ret = tracing_check_open_get_tr(tr);
> +	if (ret)
> +		return ret;
> +
> +	ret = seq_open(file, &last_boot_seq_ops);
> +	if (ret) {
> +		trace_array_put(tr);
> +		return ret;
> +	}
> +
> +	m = file->private_data;
> +	m->private = tr;
> +
> +	return 0;
>  }
>  
>  static int tracing_buffer_meta_open(struct inode *inode, struct file *filp)
> @@ -7533,10 +7610,10 @@ static const struct file_operations trace_time_stamp_mode_fops = {
>  };
>  
>  static const struct file_operations last_boot_fops = {
> -	.open		= tracing_open_generic_tr,
> -	.read		= tracing_last_boot_read,
> -	.llseek		= generic_file_llseek,
> -	.release	= tracing_release_generic_tr,
> +	.open		= tracing_last_boot_open,
> +	.read		= seq_read,
> +	.llseek		= seq_lseek,
> +	.release	= tracing_seq_release,
>  };
>  
>  #ifdef CONFIG_TRACER_SNAPSHOT
> -- 
> 2.45.2
> 
> 


-- 
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>