implement fmtmsg function

contributed by Isaac Dunham. this seems to be the last interface that
was missing for complete POSIX 2008 base + XSI coverage.

include/fmtmsg.h

+#ifndef _FMTMSG_H
+#define _FMTMSG_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define MM_HARD		1
+#define MM_SOFT		2
+#define MM_FIRM		4
+
+#define MM_APPL		8
+#define MM_UTIL		16
+#define MM_OPSYS	32
+
+#define MM_RECOVER	64
+#define MM_NRECOV	128
+
+#define MM_PRINT	256
+#define MM_CONSOLE	512
+
+#define MM_NULLMC	0L
+
+#define MM_HALT		1
+#define MM_ERROR	2
+#define MM_WARNING	3
+#define MM_INFO		4
+#define MM_NOSEV	0
+
+#define MM_OK		0
+#define MM_NOTOK	(-1)
+#define MM_NOMSG	1
+#define MM_NOCON	4
+
+#define MM_NULLLBL	((char*)0)
+#define MM_NULLTXT	((char*)0)
+#define MM_NULLACT	((char*)0)
+#define MM_NULLTAG	((char*)0)
+#define MM_NULLSEV	0
+
+int fmtmsg(long, const char *, int, const char *, const char *, const char *);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif

src/misc/fmtmsg.c

+/* Public domain fmtmsg()
+ * Written by Isaac Dunham, 2014
+ */
+#include <fmtmsg.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <pthread.h>
+
+/*
+ * If lstr is the first part of bstr, check that the next char in bstr
+ * is either \0 or :
+ */
+static int _strcolcmp(const char *lstr, const char *bstr)
+{
+	size_t i = 0;
+	while (lstr[i] && bstr[i] && (bstr[i] == lstr[i])) i++;
+	if ( lstr[i] || (bstr[i] && bstr[i] != ':')) return 1;
+	return 0;
+}
+
+int fmtmsg(long classification, const char *label, int severity,
+           const char *text, const char *action, const char *tag)
+{
+	int ret = 0, i, consolefd, verb = 0;
+	char *errstring = MM_NULLSEV, *cmsg = getenv("MSGVERB");
+	char *const msgs[] = {
+		"label", "severity", "text", "action", "tag", NULL
+	};
+	int cs;
+
+	pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
+
+	if (severity == MM_HALT) errstring = "HALT: ";
+	else if (severity == MM_ERROR) errstring = "ERROR: ";
+	else if (severity == MM_WARNING) errstring = "WARNING: ";
+	else if (severity == MM_INFO) errstring = "INFO: ";
+
+	if (classification & MM_CONSOLE) {
+		consolefd = open("/dev/console", O_WRONLY);
+		if (consolefd < 0) {
+			ret = MM_NOCON;
+		} else {
+			if (dprintf(consolefd, "%s%s%s%s%s%s%s%s\n",
+			            label?label:"", label?": ":"",
+			            severity?errstring:"", text?text:"",
+			            action?"\nTO FIX: ":"",
+			            action?action:"", action?" ":"",
+			            tag?tag:"" )<1)
+				ret = MM_NOCON;
+			close(consolefd);
+		}
+	}
+
+	if (classification & MM_PRINT) {
+		while (cmsg && cmsg[0]) {
+			for(i=0; msgs[i]; i++) {
+				if (!_strcolcmp(msgs[i], cmsg)) break;
+			}
+			if (msgs[i] == NULL) {
+				//ignore MSGVERB-unrecognized component
+				verb = 0xFF;
+				break;
+			} else {
+				verb |= (1 << i);
+				cmsg = strchr(cmsg, ':');
+				if (cmsg) cmsg++;
+			}
+		}
+		if (!verb) verb = 0xFF;
+		if (dprintf(2, "%s%s%s%s%s%s%s%s\n",
+		            (verb&1 && label) ? label : "",
+		            (verb&1 && label) ? ": " : "",
+		            (verb&2 && severity) ? errstring : "",
+		            (verb&4 && text) ? text : "",
+		            (verb&8 && action) ? "\nTO FIX: " : "",
+		            (verb&8 && action) ? action : "",
+		            (verb&8 && action) ? " " : "",
+		            (verb&16 && tag) ? tag : "" ) < 1)
+			ret |= MM_NOMSG;
+	}
+	if ((ret & (MM_NOCON|MM_NOMSG)) == (MM_NOCON|MM_NOMSG))
+		ret = MM_NOTOK;
+
+	pthread_setcancelstate(cs, 0);
+
+	return ret;
+}