tools/syz-declextract: store interfaces info in a text file

One line per interface allows to use all power of unix utilities
to process these files. For example the following command
allow to select all unpriviledged interfaces present in one kernel
but not in another:

comm -23 <(cat auto1.info | grep access:user | cut -f -2 | sort) \
	<(cat auto2.info | cut -f -2 | sort)

1 files changed, 31 insertions, 13 deletions

diff --git a/tools/syz-declextract/run.go b/tools/syz-declextract/run.go
index 332a8b9a0..181fca96c 100644
--- a/tools/syz-declextract/run.go
+++ b/tools/syz-declextract/run.go
@@ -5,6 +5,7 @@ package main
 
 import (
 	"bufio"
+	"bytes"
 	"encoding/json"
 	"errors"
 	"flag"
@@ -102,11 +103,8 @@ func main() {
 	writeDescriptions(desc)
 
 	ifaces := finishInterfaces(interfaces, extractor)
-	data, err := json.MarshalIndent(ifaces, "", "\t")
-	if err != nil {
-		tool.Failf("failed to marshal interfaces: %v", err)
-	}
-	if err := osutil.WriteFile(autoFile+".json", data); err != nil {
+	ifacesData := serializeInterfaces(ifaces)
+	if err := osutil.WriteFile(autoFile+".info", ifacesData); err != nil {
 		tool.Fail(err)
 	}
 }
@@ -152,14 +150,14 @@ type output struct {
 }
 
 type Interface struct {
-	Type               string   `json:"type"`
-	Name               string   `json:"name"`
-	Files              []string `json:"files"`
-	Func               string   `json:"func,omitempty"`
-	Access             string   `json:"access,omitempty"`
-	Subsystems         []string `json:"subsystems,omitempty"`
-	ManualDescriptions bool     `json:"has_manual_descriptions"`
-	AutoDescriptions   bool     `json:"has_auto_descriptions"`
+	Type               string
+	Name               string
+	Files              []string
+	Func               string
+	Access             string
+	Subsystems         []string
+	ManualDescriptions bool
+	AutoDescriptions   bool
 
 	identifyingConst string
 }
@@ -168,6 +166,23 @@ func (iface *Interface) ID() string {
 	return fmt.Sprintf("%v/%v", iface.Type, iface.Name)
 }
 
+func serializeInterfaces(ifaces []Interface) []byte {
+	w := new(bytes.Buffer)
+	for _, iface := range ifaces {
+		fmt.Fprintf(w, "%v\t%v\tfunc:%v\taccess:%v\tmanual_desc:%v\tauto_desc:%v",
+			iface.Type, iface.Name, iface.Func, iface.Access,
+			iface.ManualDescriptions, iface.AutoDescriptions)
+		for _, file := range iface.Files {
+			fmt.Fprintf(w, "\tfile:%v", file)
+		}
+		for _, subsys := range iface.Subsystems {
+			fmt.Fprintf(w, "\tsubsystem:%v", subsys)
+		}
+		fmt.Fprintf(w, "\n")
+	}
+	return w.Bytes()
+}
+
 func finishInterfaces(m map[string]Interface, extractor *subsystem.Extractor) []Interface {
 	var interfaces []Interface
 	for _, iface := range m {
@@ -181,6 +196,9 @@ func finishInterfaces(m map[string]Interface, extractor *subsystem.Extractor) []
 			iface.Subsystems = append(iface.Subsystems, s.Name)
 		}
 		slices.Sort(iface.Subsystems)
+		if iface.Access == "" {
+			iface.Access = "unknown"
+		}
 		interfaces = append(interfaces, iface)
 	}
 	slices.SortFunc(interfaces, func(a, b Interface) int {