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From: Grant Likely <grant.likely@secretlab.ca>
To: Pantelis Antoniou <panto@antoniou-consulting.com>,
	Joe Perches <joe@perches.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Rob Herring <robherring2@gmail.com>,
	Randy Dunlap <rdunlap@infradead.org>,
	linux-doc@vger.kernel.org, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] of: Custom printk format specifier for device node
Date: Mon, 30 Mar 2015 12:04:32 -0700	[thread overview]
Message-ID: <20150330190432.42192C40A67@trevor.secretlab.ca> (raw)
In-Reply-To: <7EBFDD59-156A-42FB-AAF0-CE4A88219794@antoniou-consulting.com>

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On Thu, 22 Jan 2015 22:31:46 +0200
, Pantelis Antoniou <panto@antoniou-consulting.com>
 wrote:
> Hi Joe,
> 
> > On Jan 21, 2015, at 19:37 , Joe Perches <joe@perches.com> wrote:
> > 
> > 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.
> > 
> 
> pO - Open Firmware
> 
> pT for tree is bad, cause we plan to use a tree type in the future in OF.

So, here's a radical thought. How about we reserve '%pO' for objects, as
in kobjects.  We'll use extra flags to narrow down specifically to
device tree nodes, but we could teach vsprintf() to treat a plain '%pO'
as plain kobject pointer, and if it is able to recognize the kobj_type,
then run a specific decoder to format it.

This also gives us a namespace for various kinds of firmware data
output. %Od could be a struct device, %On for device tree node, %Oa for
an ACPI node, etc.

> 
> >> 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@konsulko.com>
> >> 
> >> 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 ?
> > 
> 
> The whole thing is optimized away when CONFIG_OF is not defined, leaving only
> the return statement.
> 
> >> +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.
> > 
> 
> OK
> 
> >> +
> >> +	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";

s/isspace()/!isalnum() to match with what the pointer() function does
when finding the end of a format string.

> > 
> > why lower case here but upper case above?
> > 
> 
> Cause '(null)' is what’s printed in string() when null is passed as a pointer.
> 
> >> +
> >> +	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?
> > 
> 
> It’s the simplest way to do the different operations for the two passes, without
> bloating the code or adding superfluous methods.
> 
> We don’t want to allocate memory, we don’t want to use stack space. We’re probably
> printing in atomic context too since device nodes don’t usually printed out
> during normal operation.

As far as I can tell from the code, the only thing that 2 passes is used
for is when the LEFT spec.flags value is not set. Instead of doing two,
what if the code generated the string right-aligned, and then if the
LEFT flag is set, shift it over the required amount, ' ' padding as
necessary? In fact, that's exactly what the dentry_name() helper does.

This is a complicated enough block of code, that I'd like to see
unittests for it added at the same time.

...

So, I'm keen enough on this feature that I've just gone ahead and played
with it this morning. The following is what I've come up with. I got rid
of the two passes, fixed up the boundary conditions, and added
unittests. I've also switched the format key to %pOn, and the separator
to ':'. ':' is never a valid character in a node name, so it should be
safe to use as a delimiter.

I've dropped the refcount decoder. I know it is useful for debugging the
core DT code, but it isn't something that will be used generally. Plus
the returned value cannot be relied upon to be stable because there may
be other code currently iterating over the tree.

---

of: Custom printk format specifier for device node

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 %pOn\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@konsulko.com>
[grant.likely: Rework to be simpler]
Signed-off-by: Grant Likely <grant.likely@linaro.org>
---
 Documentation/printk-formats.txt             |  28 ++++++++
 drivers/of/unittest-data/tests-platform.dtsi |   4 +-
 drivers/of/unittest.c                        |  58 +++++++++++++++
 lib/vsprintf.c                               | 101 +++++++++++++++++++++++++++
 4 files changed, 190 insertions(+), 1 deletion(-)

diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
index 5a615c14f75d..f0dc2fd229e4 100644
--- a/Documentation/printk-formats.txt
+++ b/Documentation/printk-formats.txt
@@ -192,6 +192,34 @@ IPv4/IPv6 addresses (generic, with port, flowinfo, scope):
 	%pISsc		1.2.3.4		or [1:2:3:4:5:6:7:8]%1234567890
 	%pISpfc		1.2.3.4:12345	or [1:2:3:4:5:6:7:8]:12345/123456789
 
+Device tree nodes:
+
+	%pOn[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
+	Without any arguments prints full_name (same as %pOnf)
+	The separator when using multiple arguments is ':'
+
+	Examples:
+
+	%pOn	/foo/bar@0			- Node full name
+	%pOnf	/foo/bar@0			- Same as above
+	%pOnfp	/foo/bar@0:10			- Node full name + phandle
+	%pOnfcF	/foo/bar@0:foo,device:--P-	- Node full name +
+	                                          major compatible string +
+						  node flags
+							D - dynamic
+							d - detached
+							P - Populated
+							B - Populated bus
+
 UUID/GUID addresses:
 
 	%pUb	00010203-0405-0607-0809-0a0b0c0d0e0f
diff --git a/drivers/of/unittest-data/tests-platform.dtsi b/drivers/of/unittest-data/tests-platform.dtsi
index eb20eeb2b062..a0c93822aee3 100644
--- a/drivers/of/unittest-data/tests-platform.dtsi
+++ b/drivers/of/unittest-data/tests-platform.dtsi
@@ -26,7 +26,9 @@
 				#size-cells = <0>;
 
 				dev@100 {
-					compatible = "test-sub-device";
+					compatible = "test-sub-device",
+						     "test-compat2",
+						     "test-compat3";
 					reg = <0x100>;
 				};
 			};
diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
index e844907c9efa..dc43209f2064 100644
--- a/drivers/of/unittest.c
+++ b/drivers/of/unittest.c
@@ -234,6 +234,63 @@ static void __init of_unittest_check_tree_linkage(void)
 	pr_debug("allnodes list size (%i); sibling lists size (%i)\n", allnode_count, child_count);
 }
 
+static void __init of_unittest_printf_one(struct device_node *np, const char *fmt,
+					  const char *expected)
+{
+	char buf[strlen(expected)+10];
+	int size, i;
+
+	/* Baseline; check conversion with a large size limit */
+	memset(buf, 0xff, sizeof(buf));
+	size = snprintf(buf, sizeof(buf) - 2, fmt, np);
+
+	/* use strcmp() instead of strncmp() here to be absolutely sure strings match */
+	unittest((strcmp(buf, expected) == 0) && (buf[size+1] == 0xff),
+		"sprintf failed; fmt='%s' expected='%s' rslt='%s'\n",
+		fmt, expected, buf);
+
+	/* Make sure length limits work */
+	size++;
+	for (i = 0; i < 2; i++, size--) {
+		/* Clear the buffer, and make sure it works correctly still */
+		memset(buf, 0xff, sizeof(buf));
+		snprintf(buf, size+1, fmt, np);
+		unittest(strncmp(buf, expected, size) == 0 && (buf[size+1] == 0xff),
+			"snprintf failed; size=%i fmt='%s' expected='%s' rslt='%s'\n",
+			size, fmt, expected, buf);
+	}
+}
+
+static void __init of_unittest_printf(void)
+{
+	struct device_node *np;
+	const char *full_name = "/testcase-data/platform-tests/test-device@1/dev@100";
+	char phandle_str[16] = "";
+
+	np = of_find_node_by_path(full_name);
+	if (!np) {
+		unittest(np, "testcase data missing\n");
+		return;
+	}
+
+	num_to_str(phandle_str, sizeof(phandle_str), np->phandle);
+
+	of_unittest_printf_one(np, "%pOn",  full_name);
+	of_unittest_printf_one(np, "%pOnf", full_name);
+	of_unittest_printf_one(np, "%pOnp", phandle_str);
+	of_unittest_printf_one(np, "%pOnP", "dev@100");
+	of_unittest_printf_one(np, "ABC %pOnP ABC", "ABC dev@100 ABC");
+	of_unittest_printf_one(np, "%10pOnP", "   dev@100");
+	of_unittest_printf_one(np, "%-10pOnP", "dev@100   ");
+	of_unittest_printf_one(of_root, "%pOnP", "/");
+	of_unittest_printf_one(np, "%pOnF", "----");
+	of_unittest_printf_one(np, "%pOnPF", "dev@100:----");
+	of_unittest_printf_one(np, "%pOnPFPc", "dev@100:----:dev@100:test-sub-device");
+	of_unittest_printf_one(np, "%pOnc", "test-sub-device");
+	of_unittest_printf_one(np, "%pOnC",
+			"\"test-sub-device\",\"test-compat2\",\"test-compat3\"");
+}
+
 struct node_hash {
 	struct hlist_node node;
 	struct device_node *np;
@@ -1888,6 +1945,7 @@ static int __init of_unittest(void)
 	of_unittest_find_node_by_name();
 	of_unittest_dynamic();
 	of_unittest_parse_phandle_with_args();
+	of_unittest_printf();
 	of_unittest_property_string();
 	of_unittest_property_copy();
 	of_unittest_changeset();
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index b235c96167d3..8a793a4560c2 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() */
@@ -1322,6 +1323,91 @@ 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[] = "----";
+	struct property *prop;
+	const char *p;
+	int ret, i, j, n;
+	char c, *start = buf;
+	struct printf_spec str_spec =
+		{ .precision = -1, .field_width = 0, .base = 10, .flags = LEFT };
+
+	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 (!isalnum(fmt[2]))
+		fmt = "Onf";
+
+	fmt += 2;
+	for (j = 0; isalnum((c = *fmt)); j++, fmt++) {
+		if (j)
+			buf = string(buf, end, ":", str_spec);
+
+		switch (c) {
+		case 'f':	/* full_name */
+			buf = string(buf, end, of_node_full_name(dn), str_spec);
+			break;
+		case 'n':	/* name */
+			buf = string(buf, end, dn->name, str_spec);
+			break;
+		case 'p':	/* phandle */
+			buf = number(buf, end, dn->phandle, str_spec);
+			break;
+		case 'P':	/* path-spec */
+			p = strrchr(of_node_full_name(dn), '/');
+			if (p[1]) /* Root node name is just "/" */
+				p++;
+			buf = string(buf, end, p, str_spec);
+			break;
+		case 'F':	/* flags */
+			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' : '-');
+			buf = string(buf, end, tbuf, str_spec);
+			break;
+		case 'c':	/* first compatible string */
+			ret = of_property_read_string(dn, "compatible", &p);
+			if (ret == 0)
+				buf = string(buf, end, p, str_spec);
+			break;
+		case 'C':	/* full compatible string list */
+			i = 0;
+			of_property_for_each_string(dn, "compatible", prop, p) {
+				buf = string(buf, end, i ? "\",\"" : "\"", str_spec);
+				buf = string(buf, end, p, str_spec);
+				i++;
+			}
+			buf = string(buf, end, "\"", str_spec);
+			break;
+		}
+	}
+
+	/* Pad out at the front or back if field_width is specified */
+	n = buf - start;
+	if (n < spec.field_width) {
+		unsigned spaces = spec.field_width - n;
+		if (!(spec.flags & LEFT)) {
+			widen(start, end, n, spaces);
+			return buf + spaces;
+		}
+		while (spaces-- && (buf < end)) {
+			if (buf < end)
+				*buf = ' ';
+			++buf;
+		}
+	}
+	return buf;
+}
+
 int kptr_restrict __read_mostly;
 
 /*
@@ -1393,6 +1479,15 @@ int kptr_restrict __read_mostly;
  *       correctness of the format string and va_list arguments.
  * - 'K' For a kernel pointer that should be hidden from unprivileged users
  * - 'NF' For a netdev_features_t
+ * - 'On[fnpPcCF]' For a device tree object
+ *                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
  * - 'h[CDN]' For a variable-length buffer, it prints it as a hex string with
  *            a certain separator (' ' by default):
  *              C colon
@@ -1544,6 +1639,12 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 			return netdev_feature_string(buf, end, ptr, spec);
 		}
 		break;
+	case 'O':
+		switch (fmt[1]) {
+		case 'n':
+			return device_node_string(buf, end, ptr, spec, fmt);
+		}
+		break;
 	case 'a':
 		return address_val(buf, end, ptr, spec, fmt);
 	case 'd':
-- 
2.1.0



  reply	other threads:[~2015-03-31  5:16 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-21 17:06 Pantelis Antoniou
2015-01-21 17:37 ` Joe Perches
2015-01-21 17:39   ` Pantelis Antoniou
2015-01-21 17:52     ` Joe Perches
2015-01-21 17:59     ` Måns Rullgård
2015-01-22 20:31   ` Pantelis Antoniou
2015-03-30 19:04     ` Grant Likely [this message]
2015-03-31 10:03       ` Pantelis Antoniou
2015-03-31 17:02         ` Grant Likely
2015-03-31 17:14           ` Pantelis Antoniou
2015-04-01  4:52         ` Grant Likely
2015-04-01  5:07           ` Joe Perches
  -- strict thread matches above, loose matches on Subject: below --
2015-01-20 14:34 Pantelis Antoniou
2015-01-20 14:47 ` Rob Herring
2015-01-20 14:52   ` Pantelis Antoniou
2015-01-20 17:59     ` Joe Perches
2015-01-20 18:06       ` Pantelis Antoniou
2015-01-20 18:16         ` Joe Perches
2015-01-20 15:24   ` Geert Uytterhoeven
2015-01-20 15:27     ` Pantelis Antoniou
2015-01-20 16:05       ` Måns Rullgård
2015-01-20 17:13         ` Rob Herring

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