Bug 106497 - better error description when problem reading font configuration

https://bugs.freedesktop.org/show_bug.cgi?id=106497

configure.ac

@@ -169,7 +169,7 @@ AC_TYPE_PID_T
 # Checks for library functions.
 AC_FUNC_VPRINTF
 AC_FUNC_MMAP
-AC_CHECK_FUNCS([link mkstemp mkostemp _mktemp_s mkdtemp getopt getopt_long getprogname getexecname rand random lrand48 random_r rand_r readlink fstatvfs fstatfs lstat])
+AC_CHECK_FUNCS([link mkstemp mkostemp _mktemp_s mkdtemp getopt getopt_long getprogname getexecname rand random lrand48 random_r rand_r readlink fstatvfs fstatfs lstat strerror strerror_r])
 
 dnl AC_CHECK_FUNCS doesn't check for header files.
 dnl posix_fadvise() may be not available in older libc.

src/fcxml.c

@@ -22,6 +22,10 @@
  * PERFORMANCE OF THIS SOFTWARE.
  */
 
+#ifdef _GNU_SOURCE
+#undef _GNU_SOURCE /* To use the POSIX version of strerror_r */
+#endif
+#include <string.h>
 #include "fcint.h"
 #include <fcntl.h>
 #include <stdarg.h>
@@ -3451,7 +3455,21 @@ _FcConfigParse (FcConfig	*config,
 	len = read (fd, buf, BUFSIZ);
 	if (len < 0)
 	{
-	    FcConfigMessage (0, FcSevereError, "failed reading config file");
+	    int errno_ = errno;
+	    char ebuf[BUFSIZ+1];
+
+#if HAVE_STRERROR_R
+	    int x FC_UNUSED;
+	    x = strerror_r (errno_, ebuf, BUFSIZ); /* make sure we use the POSIX version of strerror_r */
+#elif HAVE_STRERROR
+	    char *tmp = strerror (errno_);
+	    size_t len = strlen (tmp);
+	    strncpy (ebuf, tmp, FC_MIN (BUFSIZ, len));
+	    ebuf[FC_MIN (BUFSIZ, len)] = 0;
+#else
+	    ebuf[0] = 0;
+#endif
+	    FcConfigMessage (0, FcSevereError, "failed reading config file: %s: %s (errno %d)", realfilename, ebuf, errno_);
 	    close (fd);
 	    goto bail1;
 	}