vsprintf: add support of '%*ph[CDN]'

There are many places in the kernel where the drivers print small buffers
as a hex string.  This patch adds a support of the variable width buffer
to print it as a hex string with a delimiter.  The idea came from Pavel
Roskin here: http://www.digipedia.pl/usenet/thread/18835/17449/

Sample output of
	pr_info("buf[%d:%d] %*phC\n", from, len, len, &buf[from]);
could be look like this:
	[ 0.726130] buf[51:8] e8:16:b6:ef:e3:74:45:6e
	[ 0.750736] buf[59:15] 31:81:b8:3f:35:49:06:ae:df:32:06:05:4a:af:55
	[ 0.757602] buf[17:5] ac:16:d5:2c:ef

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 55 insertions, 0 deletions

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 225aa683e175..0e337541f005 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -655,6 +655,50 @@ char *resource_string(char *buf, char *end, struct resource *res,
 }
 
 static noinline_for_stack
+char *hex_string(char *buf, char *end, u8 *addr, struct printf_spec spec,
+                 const char *fmt)
+{
+        int i, len = 1;         /* if we pass '%ph[CDN]', field witdh remains
+                                   negative value, fallback to the default */
+        char separator;
+
+        if (spec.field_width == 0)
+                /* nothing to print */
+                return buf;
+
+        if (ZERO_OR_NULL_PTR(addr))
+                /* NULL pointer */
+                return string(buf, end, NULL, spec);
+
+        switch (fmt[1]) {
+        case 'C':
+                separator = ':';
+                break;
+        case 'D':
+                separator = '-';
+                break;
+        case 'N':
+                separator = 0;
+                break;
+        default:
+                separator = ' ';
+                break;
+        }
+
+        if (spec.field_width > 0)
+                len = min_t(int, spec.field_width, 64);
+
+        for (i = 0; i < len && buf < end - 1; i++) {
+                buf = hex_byte_pack(buf, addr[i]);
+
+                if (buf < end && separator && i != len - 1)
+                        *buf++ = separator;
+        }
+
+        return buf;
+}
+
+static noinline_for_stack
 char *mac_address_string(char *buf, char *end, u8 *addr,
                          struct printf_spec spec, const char *fmt)
 {
@@ -974,6 +1018,13 @@ 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
+ * - 'h[CDN]' For a variable-length buffer, it prints it as a hex string with
+ *            a certain separator (' ' by default):
+ *              C colon
+ *              D dash
+ *              N no separator
+ *            The maximum supported length is 64 bytes of the input. Consider
+ *            to use print_hex_dump() for the larger input.
  *
  * Note: The difference between 'S' and 'F' is that on ia64 and ppc64
  * function pointers are really function descriptors, which contain a
@@ -1007,6 +1058,8 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
         case 'R':
         case 'r':
                 return resource_string(buf, end, ptr, spec, fmt);
+        case 'h':
+                return hex_string(buf, end, ptr, spec, fmt);
         case 'M':                       /* Colon separated: 00:01:02:03:04:05 */
         case 'm':                       /* Contiguous: 000102030405 */
                                         /* [mM]F (FDDI) */
@@ -1296,6 +1349,8 @@ qualifier:
  * %pI6c print an IPv6 address as specified by RFC 5952
  * %pU[bBlL] print a UUID/GUID in big or little endian using lower or upper
  *   case.
+ * %*ph[CDN] a variable-length hex string with a separator (supports up to 64
+ *           bytes of the input)
  * %n is ignored
  *
  * ** Please update Documentation/printk-formats.txt when making changes **