Re: [Libguestfs] [PATCH v2 2/4] common/utils: Move libxml2 writer macros to a common header file.

In some places when generating XML output in C code we use some clever macros: start_element ("memory") { attribute ("unit", "MiB"); string ("%d", g->memsize); } end_element (); This commit which is mostly refactoring moves the repeated definitions of these macros into a common header file. I also took this opportunity to change / clean up the macros: - The macros are now documented properly. - comment() and empty_element() macros are now available everywhere. - Error handling has been made generic. - Added do..while(0) around some of the macros to make them safe to use in all contexts. - Both string() and attribute() take a format string (previously there were string_format() and attribute_format() variants).