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

[Pantelis Antoniou]

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);

A verbose format specifier (1-2) can be used to print extra
information about the node like its phandle and node flags.

Signed-off-by: Pantelis Antoniou <pantelis.antoniou@xxxxxxxxxxxx>
---
 Documentation/printk-formats.txt | 18 +++++++++++
 lib/vsprintf.c                   | 67 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 85 insertions(+)

diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
index 5a615c1..6ad199f 100644
--- a/Documentation/printk-formats.txt
+++ b/Documentation/printk-formats.txt
@@ -231,6 +231,24 @@ 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{,1,2}
+
+	For printing device tree nodes. The (optional) number is the verbosity
+	level.
+
+	Examples:
+
+	%pO	/foo/bar@0		- Node full name
+	%pO0	/foo/bar@0		- Same as above
+	%pO1	/foo/bar@0[10]		- Node full name + phandle
+	%pO2	/foo/bar@0[10:DdPB]	- Node full name + phandle + 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
index ec337f6..72896cc 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -29,6 +29,7 @@
 #include <linux/dcache.h>
 #include <linux/cred.h>
 #include <net/addrconf.h>
+#include <linux/of.h>
 
 #include <asm/page.h>		/* for PAGE_SIZE */
 #include <asm/sections.h>	/* for dereference_function_descriptor() */
@@ -1240,6 +1241,68 @@ char *address_val(char *buf, char *end, const void *addr,
 	return number(buf, end, num, spec);
 }
 
+#if IS_ENABLED(CONFIG_OF)
+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:xxxx]") + 1];
+	const char *full_name;
+	int verbosity, len, flen, i;
+
+	if ((unsigned long)dn < PAGE_SIZE)
+		return string(buf, end, "(null)", spec);
+
+	full_name = of_node_full_name(dn);
+	verbosity = 0;
+	if (fmt[1] >= '0' && fmt[1] <= '2')
+		verbosity = fmt[1] - '0';
+
+	/* fast and simple case */
+	switch (verbosity) {
+	default:
+	case 0:
+		tbuf[0] = '\0';
+		break;
+	case 1:
+		snprintf(tbuf, sizeof(tbuf), "[%u]",
+			(u32)dn->phandle);
+		break;
+	case 2:
+		snprintf(tbuf, sizeof(tbuf), "[%u:%c%c%c%c]",
+			(u32)dn->phandle,
+			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' : '-');
+		break;
+	}
+	flen = strlen(full_name);
+	len = flen + strlen(tbuf);
+	if (spec.precision > 0 && len > spec.precision)
+		len = spec.precision;
+
+	if (!(spec.flags & LEFT)) {
+		while (len < spec.field_width--) {
+			if (buf < end)
+				*buf = ' ';
+			++buf;
+		}
+	}
+	for (i = 0; i < len; ++i) {
+		if (buf < end)
+			*buf = i < flen ? full_name[i] : tbuf[i - flen];
+		++buf;
+	}
+	while (len < spec.field_width--) {
+		if (buf < end)
+			*buf = ' ';
+		++buf;
+	}
+	return buf;
+}
+#endif
+
 int kptr_restrict __read_mostly;
 
 /*
@@ -1459,6 +1522,10 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 		return dentry_name(buf, end,
 				   ((const struct file *)ptr)->f_path.dentry,
 				   spec, fmt);
+#if IS_ENABLED(CONFIG_OF)
+	case 'O':
+		return device_node_string(buf, end, ptr, spec, fmt);
+#endif
 	}
 	spec.flags |= SMALL;
 	if (spec.field_width == -1) {
-- 
1.7.12

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/