Added errno, strerror and the "%m" printf metacharacter. These will allow

us to return proper PXE status codes, while simultaneously allowing for
more consistent error reporting (complete with verbose error messages as a
build-time option).

src/core/errno.c

@@ -0,0 +1,29 @@
+#include "errno.h"
+#include "vsprintf.h"
+
+/* Global "last error" number */
+int errno;
+
+static struct errortab errortab_start[0] __table_start(errortab);
+static struct errortab errortab_end[0] __table_end(errortab);
+
+/*
+ * Retrieve string representation of error number.
+ *
+ * If error not found in the error table, generate a generic "Error
+ * 0x0000" message.
+ *
+ */
+const char * strerror ( int errno ) {
+	static char *generic_message = "Error 0x0000";
+	struct errortab *errortab;
+
+	for ( errortab = errortab_start ; errortab < errortab_end ;
+	      errortab++ ) {
+		if ( errortab->errno == errno )
+			return errortab->text;
+	}
+
+	sprintf ( generic_message + 8, "%hx", errno );
+	return generic_message;
+}

src/core/vsprintf.c

@@ -2,6 +2,7 @@
 #include "if_ether.h" /* for ETH_ALEN */
 #include "limits.h" /* for CHAR_BIT */
 #include "console.h"
+#include "errno.h"
 #include "vsprintf.h"
 
 #define LONG_SHIFT  ((int)((sizeof(unsigned long)*CHAR_BIT) - 4))
@@ -31,7 +32,8 @@ PRINTF and friends
 **************************************************************************/
 static int vsprintf(char *buf, const char *fmt, va_list args)
 {
-	char *p, *s;
+	const char *p;
+	char *s;
 	s = buf;
 	for ( ; *fmt != '\0'; ++fmt) {
 		if (*fmt != '%') {
@@ -49,8 +51,10 @@ static int vsprintf(char *buf, const char *fmt, va_list args)
 		if (*fmt == 's') {
 			for(p = va_arg(args, char *); *p != '\0'; p++) 
 				buf ? *s++ = *p : putchar(*p);
-		}
-		else {	/* Length of item is bounded */
+		} else if (*fmt == 'm') {
+			for(p = strerror(errno); *p != '\0'; p++)
+				buf ? *s++ = *p : putchar(*p);
+		} else {	/* Length of item is bounded */
 			char tmp[40], *q = tmp;
 			int alt = 0;
 			int shift = INT_SHIFT;
@@ -93,7 +97,7 @@ static int vsprintf(char *buf, const char *fmt, va_list args)
 					*q++ = "0123456789ABCDEF"[(h >> shift) & 0xF] | ncase;
 			}
 			else if (*fmt == 'd') {
-				char *r;
+				char *r, *t;
 				long i;
 				if (shift > INT_SHIFT) {
 					i = va_arg(args, long);
@@ -104,17 +108,17 @@ static int vsprintf(char *buf, const char *fmt, va_list args)
 					*q++ = '-';
 					i = -i;
 				}
-				p = q;		/* save beginning of digits */
+				t = q;		/* save beginning of digits */
 				do {
 					*q++ = '0' + (i % 10);
 					i /= 10;
 				} while (i);
 				/* reverse digits, stop in middle */
 				r = q;		/* don't alter q */
-				while (--r > p) {
+				while (--r > t) {
 					i = *r;
-					*r = *p;
-					*p++ = i;
+					*r = *t;
+					*t++ = i;
 				}
 			}
 			else if (*fmt == '@') {
@@ -129,7 +133,7 @@ static int vsprintf(char *buf, const char *fmt, va_list args)
 				--q;
 			}
 			else if (*fmt == '!') {
-				char *r;
+				const char *r;
 				p = va_arg(args, char *);
 				for (r = p + ETH_ALEN; p < r; ++p)
 					q += sprintf(q, "%hhX:", *p);