newt/builder: read BOOTUTIL_MAX_IMG_SECTORS from syscfg for boot trailer

Boot trailer size was hardcoded to 128 sectors, ignoring the value
set in syscfg. This caused mismatches between trailer size and
the actual image size when BOOTUTIL_MAX_IMG_SECTORS was set to
value other than 128, potentially making images not fit
in the slot. Now the trailer size is calculated based on the syscfg
value.

Author: wiktorkwiatkowski

newt/builder/targetbuild.go

@@ -773,29 +773,37 @@ func (t *TargetBuilder) InjectSetting(key string, value string) {
 	t.injectedSettings.Set(key, value)
 }
 
-// Calculates the size of a single boot trailer.  This is the amount of flash
-// that must be reserved at the end of each image slot.
-func (t *TargetBuilder) bootTrailerSize() int {
-	var minWriteSz int
+// Retrieves an integer syscfg flag or returns the default value.
+func getSettingIntValue(settings map[string]syscfg.CfgEntry, settingName string, defaultValue int) int {
 
-	entry, ok := t.res.Cfg.Settings["MCU_FLASH_MIN_WRITE_SIZE"]
+	var intValue int
+	entry, ok := settings[settingName]
 	if !ok {
 		util.StatusMessage(util.VERBOSITY_DEFAULT,
-			"* Warning: target does not define MCU_FLASH_MIN_WRITE_SIZE "+
-				"setting; assuming a value of 1.\n")
-		minWriteSz = 1
+			"* Warning: target does not define %s "+
+				"setting; assuming a value of %d.\n", settingName, defaultValue)
+		intValue = defaultValue
 	} else {
 		val, err := util.AtoiNoOct(entry.Value)
 		if err != nil {
 			util.StatusMessage(util.VERBOSITY_DEFAULT,
 				"* Warning: target specifies invalid non-integer "+
-					"MCU_FLASH_MIN_WRITE_SIZE setting; assuming a "+
-					"value of 1.\n")
-			minWriteSz = 1
+					"%s setting; assuming a "+
+					"value of %d.\n", settingName, defaultValue)
+			intValue = defaultValue
 		} else {
-			minWriteSz = val
+			intValue = val
 		}
 	}
+	return intValue
+}
+
+// Calculates the size of a single boot trailer.  This is the amount of flash
+// that must be reserved at the end of each image slot.
+func (t *TargetBuilder) bootTrailerSize() int {
+
+	minWriteSz := getSettingIntValue(t.res.Cfg.Settings, "MCU_FLASH_MIN_WRITE_SIZE", 1)
+	maxImgSectors := getSettingIntValue(t.res.Cfg.Settings, "BOOTUTIL_MAX_IMG_SECTORS", 128)
 
 	/* Mynewt boot trailer format:
 	 *
@@ -815,11 +823,11 @@ func (t *TargetBuilder) bootTrailerSize() int {
 	 */
 
 	tsize := 16 + // Magic.
-		128*minWriteSz*3 + // Swap status.
+		maxImgSectors*minWriteSz*3 + // Swap status.
 		minWriteSz + // Copy done.
 		minWriteSz // Image Ok.
 
-	log.Debugf("Min-write-size=%d; boot-trailer-size=%d", minWriteSz, tsize)
+	log.Debugf("Min-write-size=%d; max-img-sectors=%d; boot-trailer-size=%d", minWriteSz, maxImgSectors, tsize)
 
 	return tsize
 }