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Date: Thu, 6 Aug 2020 14:45:30 -0400 From: Sean Paul <sean@...rly.run> To: Steven Rostedt <rostedt@...dmis.org> Cc: LKML <linux-kernel@...r.kernel.org> Subject: Re: tracing: Add trace_array_init_printk() to initialize instance trace_printk() buffers On Thu, Aug 6, 2020 at 12:57 PM Steven Rostedt <rostedt@...dmis.org> wrote: > > From: "Steven Rostedt (VMware)" <rostedt@...dmis.org> > > As trace_array_printk() used with not global instances will not add noise to > the main buffer, they are OK to have in the kernel (unlike trace_printk()). > This require the subsystem to create their own tracing instance, and the > trace_array_printk() only writes into those instances. > > Add trace_array_init_printk() to initialize the trace_printk() buffers > without printing out the WARNING message. > > Reported-by: Sean Paul <sean@...rly.run> With the addition of exporting the symbol (which you pointed out on IRC), this LGTM. Thanks again for being so accommodating! Reviewed-by: Sean Paul <sean@...rly.run> > Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org> > --- > kernel/trace/trace.c | 43 +++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 43 insertions(+) > > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c > index 06c0feae5ff9..48b608d9c5b1 100644 > --- a/kernel/trace/trace.c > +++ b/kernel/trace/trace.c > @@ -3129,6 +3129,9 @@ static int alloc_percpu_trace_buffer(void) > { > struct trace_buffer_struct *buffers; > > + if (trace_percpu_buffer) > + return 0; > + > buffers = alloc_percpu(struct trace_buffer_struct); > if (MEM_FAIL(!buffers, "Could not allocate percpu trace_printk buffer")) > return -ENOMEM; > @@ -3331,6 +3334,26 @@ int trace_array_vprintk(struct trace_array *tr, > return __trace_array_vprintk(tr->array_buffer.buffer, ip, fmt, args); > } > > +/** > + * trace_array_printk - Print a message to a specific instance > + * @tr: The instance trace_array descriptor > + * @ip: The instruction pointer that this is called from. > + * @fmt: The format to print (printf format) > + * > + * If a subsystem sets up its own instance, they have the right to > + * printk strings into their tracing instance buffer using this > + * function. Note, this function will not write into the top level > + * buffer (use trace_printk() for that), as writing into the top level > + * buffer should only have events that can be individually disabled. > + * trace_printk() is only used for debugging a kernel, and should not > + * be ever encorporated in normal use. > + * > + * trace_array_printk() can be used, as it will not add noise to the > + * top level tracing buffer. > + * > + * Note, trace_array_init_printk() must be called on @tr before this > + * can be used. > + */ > __printf(3, 0) > int trace_array_printk(struct trace_array *tr, > unsigned long ip, const char *fmt, ...) > @@ -3355,6 +3378,26 @@ int trace_array_printk(struct trace_array *tr, > } > EXPORT_SYMBOL_GPL(trace_array_printk); > > +/** > + * trace_array_init_printk - Initialize buffers for trace_array_printk() > + * @tr: The trace array to initialize the buffers for > + * > + * As trace_array_printk() only writes into instances, they are OK to > + * have in the kernel (unlike trace_printk()). This needs to be called > + * before trace_array_printk() can be used on a trace_array. > + */ > +int trace_array_init_printk(struct trace_array *tr) > +{ > + if (!tr) > + return -ENOENT; > + > + /* This is only allowed for created instances */ > + if (tr == &global_trace) > + return -EINVAL; > + > + return alloc_percpu_trace_buffer(); > +} > + > __printf(3, 4) > int trace_array_printk_buf(struct trace_buffer *buffer, > unsigned long ip, const char *fmt, ...) > -- > 2.25.4 >
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