libdm: add human R|readable units

When showing sizes with 'H|human' units we do use standard rounding.
This however is confusing users from time to time,
when the printed number uses some biger units i.e. GiB and there is just
tiny fraction of space missing.

So here is some real-life example with new 'r' unit.

$lvs

  LV    VG Attr       LSize  Pool Origin
  lvol0 vg -wi-a-----  1.99g
  lvol1 vg -wi-a----- <2.00g
  lvol2 vg -wi-a----- <2.01g

Meaning is - lvol1 has 'slightly' less then 2.00g - from sign '<' user
can be aware the LV doesn't have full 2.00GiB in size so he
will be less surpriced allocation of 2G volume will not succeed.

$ vgs
  VG #PV #LV #SN Attr   VSize  VFree
  vg   2   2   0 wz--n- <6,00g <2,01g

For uses needing  'old'  undecorated human unit simply will continue
to use 'H|h' units.

The new R|r  may further change when we would recongnize some
other way how to improve readability.

WHATS_NEW

@@ -1,5 +1,6 @@
 Version 2.02.169 - 
 =====================================
+  Use new default units 'r' for displaying sizes.
   Also unmount mount point on top of MD device if using blkdeactivate -u.
   Restore check preventing resize of cache type volumes (2.02.158).
   Add missing udev sync when flushing dirty cache content.

WHATS_NEW_DM

@@ -1,5 +1,6 @@
 Version 1.02.138 - 
 =====================================
+  Support new R|r human readable units output format.
   Thin dmeventd plugin reacts faster on lvextend failure path with umount.
   Add dm_stats_bind_from_fd() to bind a stats handle from a file descriptor.
   Do not try call callback when reverting activation on error path.

conf/example.conf.in

@@ -665,7 +665,7 @@ global {
 
 	# Configuration option global/units.
 	# Default value for --units argument.
-	units = "h"
+	units = "r"
 
 	# Configuration option global/si_unit_consistency.
 	# Distinguish between powers of 1024 and 1000 bytes.

lib/config/defaults.h

@@ -176,7 +176,7 @@
 #define DEFAULT_INDENT 1
 #define DEFAULT_ABORT_ON_INTERNAL_ERRORS 0
 #define DEFAULT_DETECT_INTERNAL_VG_CACHE_CORRUPTION 0
-#define DEFAULT_UNITS "h"
+#define DEFAULT_UNITS "r"
 #define DEFAULT_SUFFIX 1
 #define DEFAULT_HOSTTAGS 0
 

libdm/libdm-string.c

@@ -468,10 +468,12 @@ const char *dm_size_to_string(struct dm_pool *mem, uint64_t size,
 	unsigned base = BASE_UNKNOWN;
 	unsigned s;
 	int precision;
+	double d;
 	uint64_t byte = UINT64_C(0);
 	uint64_t units = UINT64_C(1024);
 	char *size_buf = NULL;
 	char new_unit_type = '\0', unit_type_buf[2];
+	const char *prefix = "";
 	const char * const size_str[][3] = {
 		/* BASE_UNKNOWN */
 		{"         ", "   ", " "},	/* [0] */
@@ -570,7 +572,7 @@ const char *dm_size_to_string(struct dm_pool *mem, uint64_t size,
 		byte = unit_factor;
 	} else {
 		/* Human-readable style */
-		if (unit_type == 'H') {
+		if (unit_type == 'H' || unit_type == 'R') {
 			units = UINT64_C(1000);
 			base = BASE_1000;
 		} else {
@@ -586,6 +588,16 @@ const char *dm_size_to_string(struct dm_pool *mem, uint64_t size,
 		for (s = 0; s < NUM_UNIT_PREFIXES && size < byte; s++)
 			byte /= units;
 
+		if ((s < NUM_UNIT_PREFIXES) &&
+		    ((unit_type == 'R') || (unit_type == 'r'))) {
+			/* When the rounding would cause difference, add '<' prefix
+			 * i.e.  2043M is more then 1.9949G prints <2.00G
+			 * This version is for 2 digits fixed precision */
+			d = 100. * (double) size / byte;
+			if (!_close_enough(floorl(d), nearbyintl(d)))
+				prefix = "<";
+		}
+
 		include_suffix = 1;
 	}
 
@@ -599,7 +611,7 @@ const char *dm_size_to_string(struct dm_pool *mem, uint64_t size,
 		precision = 2;
 	}
 
-	snprintf(size_buf, SIZE_BUF - 1, "%.*f%s", precision,
+	snprintf(size_buf, SIZE_BUF - 1, "%s%.*f%s", prefix, precision,
 		 (double) size / byte, include_suffix ? size_str[base + s][suffix_type] : "");
 
 	return size_buf;
@@ -639,6 +651,8 @@ uint64_t dm_units_to_factor(const char *units, char *unit_type,
 	switch (*units) {
 	case 'h':
 	case 'H':
+	case 'r':
+	case 'R':
 		multiplier = v = UINT64_C(1);
 		*unit_type = *units;
 		break;