Having decided not to provide a libmemstat(3) error number to text

conversion routine, now change my mind and add one, memstat_strerror(3),
which returns a const char * pointer to a string describing the error,
to be used on the results of memstat_mtl_geterror().

While here, also correct a minor typo in the HISTORY man page.

Pointers on improving ease of internationalization would be
appreciated.

MFC after:	1 day

lib/libmemstat/Makefile

@@ -17,6 +17,7 @@ MLINKS+=	libmemstat.3 memstat_mtl_next.3
 MLINKS+=	libmemstat.3 memstat_mtl_find.3
 MLINKS+=	libmemstat.3 memstat_mtl_free.3
 MLINKS+=	libmemstat.3 memstat_mtl_geterror.3
+MLINKS+=	libmemstat.3 memstat_strerror.3
 MLINKS+=	libmemstat.3 memstat_sysctl_all.3
 MLINKS+=	libmemstat.3 memstat_sysctl_malloc.3
 MLINKS+=	libmemstat.3 memstat_sysctl_uma.3

lib/libmemstat/libmemstat.3

@@ -35,6 +35,9 @@
 .Sh SYNOPSIS
 .In sys/types.h
 .In memstat.h
+.Ss General Functions
+.Ft const char *
+.Fn memstat_strerror "int error"
 .Ss Memory Type List Management Functions
 .Ft struct memory_type_list *
 .Fn memstat_mtl_alloc "void"
@@ -150,7 +153,9 @@ Repeated calls will incrementally update the list of memory types, permitting
 tracking over time without recreating all list state.
 If an error is detected during a query call, error condition information may
 be retrieved using
-.Fn memstat_mtl_geterror .
+.Fn memstat_mtl_geterror ,
+and converted to a user-readable string using
+.Fn memstat_strerror .
 .Pp
 Freeing the list will free all memory type data in the list, and so
 invalidates any outstanding pointers to entries in the list.
@@ -356,7 +361,10 @@ on success, or
 on failure.
 If a failure is returned, the list error access method,
 .Fn memstat_mtl_geterror ,
-may be used to retrieve the error state.  Possible error values are:
+may be used to retrieve the error state.
+The string representation of the error may be retrieved using
+.Fn memstat_strerror .
+Possible error values are:
 .Pp
 .Bl -tag -width "MEMSTAT_ERROR_TOOMANYCPUS" -compact -offset wee
 .It Dv MEMSTAT_ERROR_UNDEFINED
@@ -426,7 +434,7 @@ printf("Mbufs: %llu\\n", (unsigned long long)mbuf_count);
 .Xr uma 9
 .Sh HISTORY
 The
-.Nm memstat
+.Nm libmemstat
 library appeared in
 .Fx 6.0 .
 .Sh AUTHORS

lib/libmemstat/memstat.c

@@ -38,6 +38,27 @@
 #include "memstat.h"
 #include "memstat_internal.h"
 
+const char *
+memstat_strerror(int error)
+{
+
+	switch (error) {
+	case MEMSTAT_ERROR_NOMEMORY:
+		return ("Cannot allocate memory");
+	case MEMSTAT_ERROR_VERSION:
+		return ("Version mismatch");
+	case MEMSTAT_ERROR_PERMISSION:
+		return ("Permission denied");
+	case MEMSTAT_ERROR_TOOMANYCPUS:
+		return ("Too many CPUs");
+	case MEMSTAT_ERROR_DATAERROR:
+		return ("Data format error");
+	case MEMSTAT_ERROR_UNDEFINED:
+	default:
+		return ("Unknown error");
+	}
+}
+
 struct memory_type_list *
 memstat_mtl_alloc(void)
 {

lib/libmemstat/memstat.h

@@ -89,6 +89,11 @@ struct memory_type;
 struct memory_type_list;
 
 __BEGIN_DECLS
+/*
+ * Functions that operate without memory type or memory type list context.
+ */
+const char	*memstat_strerror(int error);
+
 /*
  * Functions for managing memory type and statistics data.
  */