[PATCH for 4.5 v2 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>
Reviewed-by: Tim Deegan <tim@xen.org>
Release-acked-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
CC: Keir Fraser <keir@xen.org>
CC: Jan Beulich <JBeulich@suse.com>

---
v2: (Suggestions from Jan and Tim)
 * Sort position of %*ph in document.  Introduce missing title for %pv.
 * Clip limit at 64 bytes rather than defaulting back to 0.
 * Don't emit a trailing space after the last byte of the hex buffer.
---
 docs/misc/printk-formats.txt |    7 +++++++
 xen/common/vsprintf.c        |   27 +++++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/docs/misc/printk-formats.txt b/docs/misc/printk-formats.txt
index 3b4323a..dee0f3e 100644
--- a/docs/misc/printk-formats.txt
+++ b/docs/misc/printk-formats.txt
@@ -3,6 +3,11 @@ Xen custom %p format options.  A subset, borrowed from Linux.
 All parameters to a %p option should be compatible with void*.  Regular
 pointers are fine.  Numbers should make use of the _p() macro.
 
+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);
+
 Symbol/Function pointers:
 
        %ps     Symbol name with condition offset and size (iff offset != 0)
@@ -16,5 +21,7 @@ Symbol/Function pointers:
        In the case that an appropriate symbol name can't be found, %p[sS] will
        fall back to '%p' and print the address in hex.
 
+Domain and vCPU information:
+
        %pv     Domain and vCPU ID from a 'struct vcpu *' (printed as
                "d<domid>v<vcpuid>")
diff --git a/xen/common/vsprintf.c b/xen/common/vsprintf.c
index e68886a..599d52a 100644
--- a/xen/common/vsprintf.c
+++ b/xen/common/vsprintf.c
@@ -272,6 +272,33 @@ 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. */
+    {
+        /* Bound user count from %* to between 0 and 64 bytes. */
+        unsigned i, nr_bytes =
+            (field_width < 0) ? 0 : (field_width > 64) ? 64 : 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);
+
+            /* Skip trailing space after final byte. */
+            if ( i == (nr_bytes - 1) )
+                break;
+
+            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