[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);

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
index ec337f6..f3e49b9 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 +1241,144 @@ char *address_val(char *buf, char *end, const void *addr,
 	return number(buf, end, num, spec);
 }
 
+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);
+
+	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";
+
+	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)
+
+		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
+
+	return buf;
+}
+
 int kptr_restrict __read_mostly;
 
 /*
@@ -1318,6 +1457,16 @@ int kptr_restrict __read_mostly;
  *           (default assumed to be phys_addr_t, passed by reference)
  * - 'd[234]' For a dentry name (optionally 2-4 last components)
  * - 'D[234]' Same as 'd' but for a struct file
+ * - 'O[fnpPcCFr]' For an DT device node
+ *                Without any optional arguments prints the full_name
+ *                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
  *
  * Note: The difference between 'S' and 'F' is that on ia64 and ppc64
  * function pointers are really function descriptors, which contain a
@@ -1459,6 +1608,8 @@ 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);
+	case 'O':
+		return device_node_string(buf, end, ptr, spec, fmt);
 	}
 	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/