Add support for a more useful resize method, that allows setting of the number
of rows, instead of requiring manual calculation.

Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>

diff -Nuar --exclude '*~' --exclude '*.txt' --exclude '*.html' --exclude '*.1' --exclude autom4te.cache --exclude bindings /dev/shm/portage/rrdtool-1.2.15/work/rrdtool-1.2.15/doc/rrdresize.pod /dev/shm/portage/rrdtool-1.2.15-r1/work/rrdtool-1.2.15/doc/rrdresize.pod
--- rrdtool-1.2.15.orig/doc/rrdresize.pod	2006-07-14 05:11:26.000000000 -0700
+++ rrdtool-1.2.15/doc/rrdresize.pod	2006-07-21 01:56:56.333392940 -0700
@@ -6,6 +6,8 @@
 
 B<rrdtool> B<resize> I<filename> I<rra-num>  B<GROW>I<|>B<SHRINK> I<rows>
 
+B<rrdtool> B<resize> I<filename> I<rra-num>  [B<+>B<->B<=>]I<rows>
+
 =head1 DESCRIPTION
 
 The B<resize> function is used to modify the number of rows in
@@ -23,17 +25,20 @@
 
 =item B<GROW>
 
-used if you want to add extra rows to an RRA. The extra rows will be inserted
-as the rows that are oldest.
+(old style) used if you want to add extra rows to an RRA. The extra rows will
+be inserted as the rows that are oldest.
 
 =item B<SHRINK>
 
-used if you want to remove rows from an RRA. The rows that will be removed
-are the oldest rows.
+(old style) used if you want to remove rows from an RRA. The rows that will be
+removed are the oldest rows.
 
-=item I<rows>
+=item [B<+>B<->B<=>]I<rows>
 
-the number of rows you want to add or remove.
+the number of rows you want to add or remove. when prefixed with any of B<+>,
+B<-> or B<=>, the B<GROW>I<|>B<SHRINK> argument is not required, and instead
+the prefix specifies to add (B<+>) I<rows>, remove (B<->) I<rows>, or set to
+exactly (B<=>) I<rows>.
 
 =back
 
diff -Nuar --exclude '*~' --exclude '*.txt' --exclude '*.html' --exclude '*.1' --exclude autom4te.cache --exclude bindings /dev/shm/portage/rrdtool-1.2.15/work/rrdtool-1.2.15/src/rrd_resize.c /dev/shm/portage/rrdtool-1.2.15-r1/work/rrdtool-1.2.15/src/rrd_resize.c
--- rrdtool-1.2.15.orig/src/rrd_resize.c	2006-07-14 05:11:26.000000000 -0700
+++ rrdtool-1.2.15/src/rrd_resize.c	2006-07-21 03:09:45.656705610 -0700
@@ -19,7 +19,7 @@
     unsigned long	l,rra;
     long		modify;
     unsigned long	target_rra;
-    int			grow=0,shrink=0;
+    int			grow=0,shrink=0,setsize=0,newstyle=0;
     char		*endptr;
 
     infilename=argv[1];
@@ -27,7 +27,7 @@
         rrd_set_error("resize.rrd is a reserved name");
         return(-1);
     }
-    if (argc!=5) {
+    if (argc!=5 && argc != 4) {
         rrd_set_error("wrong number of parameters");
         return(-1);
     }
@@ -36,20 +36,39 @@
 
     if (!strcmp(argv[3],"GROW")) grow=1;
     else if (!strcmp(argv[3],"SHRINK")) shrink=1;
+	else if (argv[3][0] == '=' || argv[3][0] == '-' || argv[3][0] == '+') newstyle=3;
     else {
         rrd_set_error("I can only GROW or SHRINK");
         return(-1);
     }
 
-    modify=strtol(argv[4],&endptr,0);
-
-    if ((modify<1)) {
-        rrd_set_error("Please grow or shrink with at least 1 row");
-        return(-1);
-    }
-
-    if (shrink) modify = -modify;
+	// if the size starts with a character (=-+) then it's the new style
+	// instead. This is an extra mode so we can allow
+	// rrdtool resize FOO.rrd 5 GROW =5
+	if(argc == 5 && (argv[4][0] == '=' || argv[4][0] == '-' || argv[4][0] == '+')) {
+		newstyle = 4;
+	}
+	if(newstyle > 0) {
+		setsize = argv[newstyle][0] == '=' ? 1 : 0;
+		/* If we see a + or a -, then the codepath is simple */
+		grow = argv[newstyle][0] == '+' ? 1 : 0;
+		shrink = argv[newstyle][0] == '-' ? 1 : 0;
+		modify=strtol(argv[newstyle]+1,&endptr,0);
+		if(modify == 0) {
+			rrd_set_error("Refusing to add/delete/set with 0 rows");
+			return(-1);
+		}
+	} else {
+		/* this is the old code branch */
+		modify=strtol(argv[4],&endptr,0);
+
+		if ((modify<1)) {
+			rrd_set_error("Please grow or shrink with at least 1 row");
+			return(-1);
+		}
 
+		if (shrink) modify = -modify;
+	}
 
     if (rrd_open(infilename, &infile, &rrdold, RRD_READWRITE)==-1) {
         rrd_set_error("could not open RRD");
@@ -68,6 +87,17 @@
         fclose(infile);
         return(-1);
     }
+	/* if we are in setsize mode, we need to work out what modify factor to use */
+	if(setsize > 0) {
+		long oldsize = rrdold.rra_def[target_rra].row_cnt;
+		long newsize = modify;
+		// old=5, new=5 => modify = 0
+		if(newsize == oldsize) {
+			rrd_set_error("RRA is already set to that size!");
+			return(-1);
+		}
+		modify = newsize-oldsize;
+	}
 
     if (modify < 0)
 	if ((long)rrdold.rra_def[target_rra].row_cnt <= -modify) {
diff -Nuar --exclude '*~' --exclude '*.txt' --exclude '*.html' --exclude '*.1' --exclude autom4te.cache --exclude bindings /dev/shm/portage/rrdtool-1.2.15/work/rrdtool-1.2.15/src/rrd_tool.c /dev/shm/portage/rrdtool-1.2.15-r1/work/rrdtool-1.2.15/src/rrd_tool.c
--- rrdtool-1.2.15.orig/src/rrd_tool.c	2006-07-14 05:11:26.000000000 -0700
+++ rrdtool-1.2.15/src/rrd_tool.c	2006-07-21 03:07:41.862541464 -0700
@@ -152,6 +152,7 @@
 
     char help_resize[] =
 	   " * resize - alter the length of one of the RRAs in an RRD\n\n"
+	   "\trrdtool resize filename rranum <+|-|=>rows\n";
 	   "\trrdtool resize filename rranum GROW|SHRINK rows\n\n";
 
     char help_xport[] =