pkg/manager: remove a dependency on grep

Instead of calling grep (the implementations of which may differ in
different environments), traverse the directory and grep files with a
special pkg/osutil helper functionality.

Author: a-nogikh

pkg/manager/diff.go

@@ -816,25 +816,21 @@ func affectedFiles(cfg *mgrconfig.Config, gitPatches [][]byte) (direct, transiti
 	for _, file := range allFiles {
 		directMap[file] = struct{}{}
 		if strings.HasSuffix(file, ".h") && cfg.KernelSrc != "" {
+			// For .h files, we want to determine all the .c files that include them.
 			// Ideally, we should combine this with the recompilation process - then we know
 			// exactly which files were affected by the patch.
-			out, err := osutil.RunCmd(time.Minute, cfg.KernelSrc, "/usr/bin/grep",
-				"-rl", "--include", `*.c`, `<`+strings.TrimPrefix(file, "include/")+`>`)
+			matching, err := osutil.GrepFiles(cfg.KernelSrc, `.c`,
+				[]byte(`<`+strings.TrimPrefix(file, "include/")+`>`))
 			if err != nil {
-				log.Logf(0, "failed to grep for the header usages: %v", err)
+				log.Logf(0, "failed to grep for includes: %s", err)
 				continue
 			}
-			lines := strings.Split(string(out), "\n")
-			if len(lines) >= maxAffectedByHeader {
+			if len(matching) >= maxAffectedByHeader {
 				// It's too widespread. It won't help us focus on anything.
-				log.Logf(0, "the header %q is included in too many files (%d)", file, len(lines))
+				log.Logf(0, "the header %q is included in too many files (%d)", file, len(matching))
 				continue
 			}
-			for _, name := range lines {
-				name = strings.TrimSpace(name)
-				if name == "" {
-					continue
-				}
+			for _, name := range matching {
 				transitiveMap[name] = struct{}{}
 			}
 		}

pkg/osutil/fileutil.go

@@ -4,8 +4,10 @@
 package osutil
 
 import (
+	"bytes"
 	"fmt"
 	"io"
+	"io/fs"
 	"os"
 	"path/filepath"
 )
@@ -81,3 +83,28 @@ func WriteTempFile(data []byte) (string, error) {
 	f.Close()
 	return f.Name(), nil
 }
+
+// GrepFiles returns the list of files (relative to root) that include target.
+// If ext is not empty, the files will be filtered by the extension.
+// The function assumes that the files are not too big and may fit in memory.
+func GrepFiles(root, ext string, target []byte) ([]string, error) {
+	var ret []string
+	err := filepath.WalkDir(root, func(path string, d fs.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+		if d.IsDir() || filepath.Ext(path) != ext {
+			return nil
+		}
+		content, err := os.ReadFile(path)
+		if err != nil {
+			return fmt.Errorf("failed to open %s: %w", path, err)
+		}
+		if bytes.Contains(content, target) {
+			rel, _ := filepath.Rel(root, path)
+			ret = append(ret, rel)
+		}
+		return nil
+	})
+	return ret, err
+}

pkg/osutil/fileutil_test.go

@@ -9,6 +9,9 @@ import (
 	"strconv"
 	"sync"
 	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestProcessTempDir(t *testing.T) {
@@ -60,3 +63,17 @@ func TestProcessTempDir(t *testing.T) {
 		}()
 	}
 }
+
+func TestGrepFiles(t *testing.T) {
+	dir := t.TempDir()
+	require.NoError(t, FillDirectory(dir, map[string]string{
+		"a.c":     `must be found`,
+		"a/b.c":   `nested`,
+		"a/b/c.c": `even more nested, must be found`,
+		"a.txt":   `must be found, but has a different extension`,
+	}))
+
+	ret, err := GrepFiles(dir, ".c", []byte(`must be found`))
+	require.NoError(t, err)
+	assert.ElementsMatch(t, []string{"a.c", "a/b/c.c"}, ret)
+}