boot/piboot: allow returning error from visitSections

We want to be able to traverse sections and make local decisions,
including that of failure, and having visitSections support an error
value is the easiest way to do that.

Signed-off-by: Zygmunt Krynicki <zygmunt.krynicki@huawei.com>

boot/piboot/piboot.go

@@ -148,7 +148,7 @@ func (pi *PiBoot) QueryActive() (slot boot.Slot, err error) {
 	// Find the configured kernel and kernel cmdline
 	var kernel, initramfs, cmdline string
 
-	err = visitSections(&configTxt, pi.FilterPredicate, func(sect *picfg.Section) {
+	err = visitSections(&configTxt, pi.FilterPredicate, func(sect *picfg.Section) error {
 		for _, param := range sect.Parameters {
 			switch param.Name {
 			case kernelParameter:
@@ -159,6 +159,7 @@ func (pi *PiBoot) QueryActive() (slot boot.Slot, err error) {
 				cmdline = param.Value
 			}
 		}
+		return nil
 	})
 	if err != nil {
 		return boot.InvalidSlot, &UnknownActiveSlotError{Err: err}
@@ -218,7 +219,7 @@ func (pi *PiBoot) TrySwitch(to boot.Slot) (err error) {
 	}
 
 	// Find the values to modify, swapping A and B around
-	err = visitSections(&configTxt, pi.FilterPredicate, func(sect *picfg.Section) {
+	err = visitSections(&configTxt, pi.FilterPredicate, func(sect *picfg.Section) error {
 		for paramIdx, param := range sect.Parameters {
 			switch param.Name {
 			case kernelParameter, cmdlineParameter, initramfsParameter:
@@ -236,6 +237,7 @@ func (pi *PiBoot) TrySwitch(to boot.Slot) (err error) {
 				sect.Parameters[paramIdx].Value = strings.Replace(param.Value, oldPrefix, newPrefix, -1)
 			}
 		}
+		return nil
 	})
 	if err != nil {
 		return err
@@ -296,7 +298,7 @@ func (pi *PiBoot) CancelSwitch() error {
 // An optional predicate function may be used to visit only matching sections.
 // The predicate is called with the effective fiters that are in effect at each
 // phase of the traversal process. Sections can be mutated by the visitor.
-func visitSections(configTxt *picfg.ConfigTxt, pred func([]condfilter.ConditionalFilter) bool, visitor func(sect *picfg.Section)) error {
+func visitSections(configTxt *picfg.ConfigTxt, pred func([]condfilter.ConditionalFilter) bool, visitor func(sect *picfg.Section) error) error {
 	var tracker condfilter.StateTracker
 
 	for _, sect := range *configTxt {
@@ -313,7 +315,9 @@ func visitSections(configTxt *picfg.ConfigTxt, pred func([]condfilter.Conditiona
 			}
 		}
 
-		visitor(&sect)
+		if err := visitor(&sect); err != nil {
+			return err
+		}
 	}
 
 	return nil