[PATCH for-4.5 1/2] xen/vsprintf: Introduce %*ph extended format specifier for hex buffers

[Andrew Cooper <andrew.cooper3@citrix.com>]

This behaves in the same way as Linux.  The 64 byte limit is arbitrary but
long enough for practical purposes.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Keir Fraser <keir@xen.org>
CC: Jan Beulich <JBeulich@suse.com>
CC: Tim Deegan <tim@xen.org>
CC: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
 docs/misc/printk-formats.txt |    6 ++++++
 xen/common/vsprintf.c        |   25 +++++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/docs/misc/printk-formats.txt b/docs/misc/printk-formats.txt
index 3b4323a..81b3651 100644
--- a/docs/misc/printk-formats.txt
+++ b/docs/misc/printk-formats.txt
@@ -18,3 +18,9 @@ Symbol/Function pointers:
 
        %pv     Domain and vCPU ID from a 'struct vcpu *' (printed as
                "d<domid>v<vcpuid>")
+
+
+Raw buffer as hex string:
+
+       %*ph    Up to 64 characters, printed as "00 01 02 ... ff".  Buffer length
+               expected via the field_width paramter. i.e. printk("%*ph", 8, buffer);
diff --git a/xen/common/vsprintf.c b/xen/common/vsprintf.c
index e68886a..4a7da1c 100644
--- a/xen/common/vsprintf.c
+++ b/xen/common/vsprintf.c
@@ -272,6 +272,31 @@ static char *pointer(char *str, char *end, const char **fmt_ptr,
     /* Custom %p suffixes. See XEN_ROOT/docs/misc/printk-formats.txt */
     switch ( fmt[1] )
     {
+    case 'h': /* Raw buffer as hex string. */
+    {
+        /*
+         * User expected to provide an explicit count using %*.  Bound between
+         * 0 and 64 bytes, defaulting to 0.
+         */
+        unsigned i, nr_bytes =
+            ((field_width < 1) || (field_width > 64)) ? 0 : field_width;
+        const uint8_t *hex_buffer = arg;
+
+        /* Consumed 'h' from the format string. */
+        ++*fmt_ptr;
+
+        for ( i = 0; i < nr_bytes; ++i )
+        {
+            /* Each byte: 2 chars, 0-padded, base 16, no hex prefix. */
+            str = number(str, end, hex_buffer[i], 16, 2, -1, ZEROPAD);
+            if ( str < end )
+                *str = ' ';
+            ++str;
+        }
+
+        return str;
+    }
+
     case 's': /* Symbol name with offset and size (iff offset != 0) */
     case 'S': /* Symbol name unconditionally with offset and size */
     {
-- 
1.7.10.4