linux-kernel - [PATCHv3] printf: Add format for 8-byte EUI-64 type

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Message-Id: <1449702413-25598-1-git-send-email-keith.busch@intel.com>
Date:	Wed,  9 Dec 2015 16:06:53 -0700
From:	Keith Busch <keith.busch@...el.com>
To:	linux-nvme@...ts.infradead.org, LKML <linux-kernel@...r.kernel.org>
Cc:	Matthew Wilcox <willy@...ux.intel.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jens Axboe <axboe@...com>,
	Christoph Hellwig <hch@...radead.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Joe Perches <joe@...ches.com>,
	Keith Busch <keith.busch@...el.com>
Subject: [PATCHv3] printf: Add format for 8-byte EUI-64 type

MAC addresses may be formed using rules based on EUI-64, which is 2 bytes
longer than a typical 6-byte MAC. This patch adds a long specifier to
the %pM format to support the extended unique identifier.

Since there are multiple valid possible permutations of format specifiers,
the decoding is done in a loop, and the default ':' separator is
initialized at declaration time. A side effect of this allows 'F' and
'R' both be specified, so these are appended to the documentation.

Signed-off-by: Keith Busch <keith.busch@...el.com>
---
>From previous version:

  Use 'while (isalpha(*++fmt))' to loop over all the format specfiers,
  and updated documentation with the new possible formats.

 Documentation/printk-formats.txt | 15 ++++++++++++---
 lib/vsprintf.c                   | 40 +++++++++++++++++++++-------------------
 2 files changed, 33 insertions(+), 22 deletions(-)

diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
index b784c27..b39eb37 100644
--- a/Documentation/printk-formats.txt
+++ b/Documentation/printk-formats.txt
@@ -136,14 +136,23 @@ Raw buffer as a hex string:
 MAC/FDDI addresses:
 
 	%pM	00:01:02:03:04:05
+	%pMl	00:01:02:03:04:05:06:07
 	%pMR	05:04:03:02:01:00
+	%pMRl	07:06:05:04:03:02:01:00
 	%pMF	00-01-02-03-04-05
+	%pMFl	00-01-02-03-04-05-06-07
+	%pMFR	05-04-03-02-01-00
+	%pMFRl	07-06-05-04-03-02-01-00
 	%pm	000102030405
+	%pml	0001020304050607
 	%pmR	050403020100
+	%pmRl	0706050403020100
 
-	For printing 6-byte MAC/FDDI addresses in hex notation. The 'M' and 'm'
-	specifiers result in a printed address with ('M') or without ('m') byte
-	separators. The default byte separator is the colon (':').
+	For printing 6 or 8-byte MAC/FDDI addresses in hex notation. The
+	'M' and 'm' specifiers result in a printed address with ('M')
+	or without ('m') byte separators. The default byte separator is
+	the colon (':'). Append 'l' to specify an 8-byte in accordance
+	with EUI-64 format.
 
 	Where FDDI addresses are concerned the 'F' specifier can be used after
 	the 'M' specifier to use dash ('-') separators instead of the default
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index f9cee8e..01b7ebd 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -889,33 +889,33 @@ static noinline_for_stack
 char *mac_address_string(char *buf, char *end, u8 *addr,
 			 struct printf_spec spec, const char *fmt)
 {
-	char mac_addr[sizeof("xx:xx:xx:xx:xx:xx")];
+	char mac_addr[sizeof("xx:xx:xx:xx:xx:xx:xx:xx")];
 	char *p = mac_addr;
-	int i;
-	char separator;
-	bool reversed = false;
-
-	switch (fmt[1]) {
-	case 'F':
-		separator = '-';
-		break;
+	int i, bytes = 6;
+	char separator = ':';
+	bool reversed = false, separate = (fmt[0] == 'M');
 
-	case 'R':
-		reversed = true;
-		/* fall through */
-
-	default:
-		separator = ':';
-		break;
+	while (isalpha(*++fmt)) {
+		switch (*fmt) {
+		case 'F':
+			separator = '-';
+			break;
+		case 'R':
+			reversed = true;
+			break;
+		case 'l':
+			bytes = 8;
+			break;
+		}
 	}
 
-	for (i = 0; i < 6; i++) {
+	for (i = 0; i < bytes; i++) {
 		if (reversed)
-			p = hex_byte_pack(p, addr[5 - i]);
+			p = hex_byte_pack(p, addr[(bytes - 1) - i]);
 		else
 			p = hex_byte_pack(p, addr[i]);
 
-		if (fmt[0] == 'M' && i != 5)
+		if (separate && i != (bytes - 1))
 			*p++ = separator;
 	}
 	*p = '\0';
@@ -1496,6 +1496,8 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
 	case 'm':			/* Contiguous: 000102030405 */
 					/* [mM]F (FDDI) */
 					/* [mM]R (Reverse order; Bluetooth) */
+					/* [mM]l (EUI-64) */
+					/* [mM][FM]l (FDDI/Reverse order EUI-64) */
 		return mac_address_string(buf, end, ptr, spec, fmt);
 	case 'I':			/* Formatted IP supported
 					 * 4:	1.2.3.4
-- 
2.6.2.307.g37023ba

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