Re: [PATCH] of: Custom printk format specifier for device node

[Joe Perches]

On Wed, 2015-01-21 at 19:06 +0200, Pantelis Antoniou wrote:
> 90% of the usage of device node's full_name is printing it out
> in a kernel message. Preparing for the eventual delayed allocation
> introduce a custom printk format specifier that is both more
> compact and more pleasant to the eye.
> 
> For instance typical use is:
> 	pr_info("Frobbing node %s\n", node->full_name);
> 
> Which can be written now as:
> 	pr_info("Frobbing node %pO\n", node);

Still disliking use of %p0.

> More fine-grained control of formatting includes printing the name,
> flag, path-spec name, reference count and others, explained in the
> documentation entry.
> 
> Signed-off-by: Pantelis Antoniou <pantelis.antoniou@xxxxxxxxxxxx>
> 
> dt-print
> ---
>  Documentation/printk-formats.txt |  29 ++++++++
>  lib/vsprintf.c                   | 151 +++++++++++++++++++++++++++++++++++++++
>  2 files changed, 180 insertions(+)
> 
> diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
> index 5a615c1..2d42c04 100644
> --- a/Documentation/printk-formats.txt
> +++ b/Documentation/printk-formats.txt
> @@ -231,6 +231,35 @@ struct va_format:
>  	Do not use this feature without some mechanism to verify the
>  	correctness of the format string and va_list arguments.
>  
> +Device tree nodes:
> +
> +	%pO[fnpPcCFr]
> +
> +	For printing device tree nodes. The optional arguments are:
> +            f device node full_name
> +            n device node name
> +            p device node phandle
> +            P device node path spec (name + @unit)
> +            F device node flags
> +            c major compatible string
> +            C full compatible string
> +            r node reference count
> +	Without any arguments prints full_name (same as %pOf)
> +	The separator when using multiple arguments is '|'
> +
> +	Examples:
> +
> +	%pO	/foo/bar@0			- Node full name
> +	%pOf	/foo/bar@0			- Same as above
> +	%pOfp	/foo/bar@0|10			- Node full name + phandle
> +	%pOfcF	/foo/bar@0|foo,device|--P-	- Node full name +
> +	                                          major compatible string +
> +						  node flags
> +							D - dynamic
> +							d - detached
> +							P - Populated
> +							B - Populated bus
> +
>  u64 SHOULD be printed with %llu/%llx:
>  
>  	printk("%llu", u64_var);
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
[]

Add #ifdef back ?

> +static noinline_for_stack
> +char *device_node_string(char *buf, char *end, struct device_node *dn,
> +			 struct printf_spec spec, const char *fmt)
> +{
> +	char tbuf[sizeof("xxxxxxxxxx") + 1];
> +	const char *fmtp, *p;
> +	int len, ret, i, j, pass;
> +	char c;
> +
> +	if (!IS_ENABLED(CONFIG_OF))
> +		return string(buf, end, "(!OF)", spec);

Not very descriptive output, maybe the address would be better.

> +
> +	if ((unsigned long)dn < PAGE_SIZE)
> +		return string(buf, end, "(null)", spec);
> +
> +	/* simple case without anything any more format specifiers */
> +	if (fmt[1] == '\0' || isspace(fmt[1]))
> +		fmt = "Of";

why lower case here but upper case above?

> +
> +	len = 0;
> +
> +	/* two passes; the first calculates length, the second fills in */
> +	for (pass = 1; pass <= 2; pass++) {
> +		if (pass == 2 && !(spec.flags & LEFT)) {
> +			/* padding */
> +			while (len < spec.field_width--) {
> +				if (buf < end)
> +					*buf = ' ';
> +				++buf;
> +			}
> +		}
> +#undef _HANDLE_CH
> +#define _HANDLE_CH(_ch) \
> +	do { \
> +		if (pass == 1) \
> +			len++; \
> +		else \
> +			if (buf < end) \
> +				*buf++ = (_ch); \
> +	} while (0)
> +#undef _HANDLE_STR
> +#define _HANDLE_STR(_str) \
> +	do { \
> +		const char *str = (_str); \
> +		if (pass == 1) \
> +			len += strlen(str); \
> +		else \
> +			while (*str && buf < end) \
> +				*buf++ = *str++; \
> +	} while (0)

This isn't pretty.  Perhaps there's a better way?

> +
> +		for (fmtp = fmt + 1, j = 0; (c = *fmtp++) != '\0'; ) {
> +			switch (c) {
> +			case 'f':	/* full_name */
> +				if (j++ > 0)
> +					_HANDLE_CH(':');
> +				_HANDLE_STR(of_node_full_name(dn));
> +				break;
> +			case 'n':	/* name */
> +				if (j++ > 0)
> +					_HANDLE_CH('|');
> +				_HANDLE_STR(dn->name);
> +				break;
> +			case 'p':	/* phandle */
> +				if (j++ > 0)
> +					_HANDLE_CH('|');
> +				snprintf(tbuf, sizeof(tbuf), "%u",
> +						(unsigned int)dn->phandle);
> +				_HANDLE_STR(tbuf);
> +				break;
> +			case 'P':	/* path-spec */
> +				if (j++ > 0)
> +					_HANDLE_CH('|');
> +				_HANDLE_STR(dn->name);
> +				/* need to tack on the @ postfix */
> +				p = strchr(of_node_full_name(dn), '@');
> +				if (p)
> +					_HANDLE_STR(p);
> +				break;
> +			case 'F':	/* flags */
> +				if (j++ > 0)
> +					_HANDLE_CH('|');
> +				snprintf(tbuf, sizeof(tbuf), "%c%c%c%c",
> +					of_node_check_flag(dn, OF_DYNAMIC) ?
> +						'D' : '-',
> +					of_node_check_flag(dn, OF_DETACHED) ?
> +						'd' : '-',
> +					of_node_check_flag(dn, OF_POPULATED) ?
> +						'P' : '-',
> +					of_node_check_flag(dn,
> +						OF_POPULATED_BUS) ?  'B' : '-');
> +				_HANDLE_STR(tbuf);
> +				break;
> +			case 'c':	/* major compatible string */
> +				if (j++ > 0)
> +					_HANDLE_CH('|');
> +				ret = of_property_read_string(dn, "compatible",
> +						&p);
> +				if (ret == 0)
> +					_HANDLE_STR(p);
> +				break;
> +			case 'C':	/* full compatible string */
> +				if (j++ > 0)
> +					_HANDLE_CH('|');
> +				i = 0;
> +				while (of_property_read_string_index(dn,
> +						"compatible", i, &p) == 0) {
> +					if (i == 0)
> +						_HANDLE_STR("\"");
> +					else
> +						_HANDLE_STR("\",\"");
> +					_HANDLE_STR(p);
> +					i++;
> +				}
> +				if (i > 0)
> +					_HANDLE_STR("\"");
> +				break;
> +			case 'r':	/* node reference count */
> +				if (j++ > 0)
> +					_HANDLE_CH('|');
> +				snprintf(tbuf, sizeof(tbuf), "%u",
> +					atomic_read(&dn->kobj.kref.refcount));
> +				_HANDLE_STR(tbuf);
> +				break;
> +			default:
> +				break;
> +			}
> +		}
> +	}
> +	/* finish up */
> +	while (buf < end && len < spec.field_width--)
> +		*buf++ = ' ';
> +#undef _HANDLE_CH
> +#undef _HANDLE_STR


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