linux-kernel - Re: [PATCH 3/4] of: Custom printk format specifier for device node

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Date:   Thu, 15 Jun 2017 14:50:05 -0700
From:   Joe Perches <joe@...ches.com>
To:     Rob Herring <robh@...nel.org>
Cc:     Frank Rowand <frowand.list@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] of: Custom printk format specifier for device node

On Thu, 2017-06-15 at 16:26 -0500, Rob Herring wrote:
> On Wed, Jun 14, 2017 at 01:56:48PM -0700, Joe Perches wrote:
> > On Wed, 2017-06-14 at 15:30 -0500, Rob Herring wrote:
> > > From: Pantelis Antoniou <pantelis.antoniou@...sulko.com>
[]
> > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> > > []
> > > @@ -1470,6 +1471,123 @@ char *flags_string(char *buf, char *end, void *flags_ptr, const char *fmt)
> > >  	return format_flags(buf, end, flags, names);
> > >  }
> > >  
> > > +static noinline_for_stack
> > > +char *device_node_gen_full_name(const struct device_node *np, char *buf, char *end)
> > > +{
> > > +	int len, ret;
> > > +
> > > +	if (!np || !np->parent)
> > > +		return buf;
> > > +
> > > +	buf = device_node_gen_full_name(np->parent, buf, end);
> > 
> > This is recursive.  How many levels of parents could there be?
> > Perhaps there should be a recursion limit.
> 
> Okay, unlike unflattening code, we can easily calculate the depth and 
> then allocate an array on the stack. So this is what I've ended up 
> with:
> 
> static int device_node_calc_depth(const struct device_node *np)
> {
> 	int d;
> 
> 	for (d = 0; np; d++)
> 		np = np->parent;
> 
> 	return d;
> }
> 
> static noinline_for_stack
> char *device_node_gen_full_name(const struct device_node *np, char *buf, char *end)
> {
> 	int i;
> 	int depth = device_node_calc_depth(np);
> 	const struct device_node *nodes[depth];
> 	const struct printf_spec strspec = {
> 		.field_width = -1,
> 		.precision = -1,
> 	};

static const struct printf_spec strspec = { etc...
and please move strspec above *nodes

> 
> 	if (!depth)
> 		return buf;
> 	/* special case for root node */
> 	if (depth == 1)
> 		return string(buf, end, "/", strspec);
> 
> 	depth--;
> 	for (i = depth - 1; i >= 0; i--) {
> 		nodes[i] = np;
> 		np = np->parent;
> 	}
> 	for (i = 0; i < depth; i++) {
> 		buf = string(buf, end, "/", strspec);
> 		buf = string(buf, end, kbasename(nodes[i]->full_name), strspec);
> 	}
> 	return buf;
> }