[build] Allow error message URI to be customised via config/branding.h

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/config/branding.h

@@ -28,6 +28,51 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #define PRODUCT_SHORT_NAME "iPXE"
 #define PRODUCT_URI "http://ipxe.org"
 
+/*
+ * Error messages
+ *
+ * iPXE error messages comprise a summary error message
+ * (e.g. "Permission denied") and a 32-bit error number.  This number
+ * is incorporated into an error URI such as
+ *
+ *   "No such file or directory (http://ipxe.org/2d0c613b)"
+ *
+ * or
+ *
+ *   "Operation not supported (http://ipxe.org/3c092003)"
+ *
+ * Users may browse to the URI within the error message, which is
+ * provided by a database running on the iPXE web site
+ * (http://ipxe.org).  This database provides details for all possible
+ * errors generated by iPXE, including:
+ *
+ * - the detailed error message (e.g. "Not an OCSP signing
+ *   certificate") to complement the summary message (e.g. "Permission
+ *   denied") which is compiled into the iPXE binary.
+ *
+ * - an instruction to the user to upgrade, if the error cannot be
+ *   generated by the latest version of iPXE.
+ *
+ * - hints on how to fix the error (e.g. "This error indicates that
+ *   the file was not found on the TFTP server.  Check that you can
+ *   retrieve the file using an alternative TFTP client, such as
+ *   tftp-hpa on Linux.")
+ *
+ * - details of which source file within the iPXE codebase generated
+ *   the error.
+ *
+ * - a direct link to the line(s) of code which generated the error.
+ *
+ * If you have a customer support team and would like your customers
+ * to contact your support team for all problems, instead of using the
+ * existing support infrastructure provided by http://ipxe.org, then
+ * you may define a custom URI to be included within error messages.
+ *
+ * Note that the custom URI is a printf() format string which must
+ * include a format specifier for the 32-bit error number.
+ */
+#define PRODUCT_ERROR_URI "http://ipxe.org/%08x"
+
 #include <config/local/branding.h>
 
 #endif /* CONFIG_BRANDING_H */

src/hci/strerror.c

@@ -2,6 +2,7 @@
 #include <string.h>
 #include <stdio.h>
 #include <ipxe/errortab.h>
+#include <config/branding.h>
 
 /** @file
  *
@@ -88,11 +89,11 @@ const char * strerror ( int errno ) {
 	/* Construct the error message */
 	if ( errortab ) {
 		snprintf ( errbuf, sizeof ( errbuf ),
-			   "%s (http://ipxe.org/%08x)",
+			   "%s (" PRODUCT_ERROR_URI ")",
 			   errortab->text, errno );
 	} else {
 		snprintf ( errbuf, sizeof ( errbuf ),
-			   "Error %#08x (http://ipxe.org/%08x)",
+			   "Error %#08x (" PRODUCT_ERROR_URI ")",
 			   errno, errno );
 	}