Always use fallocate() on Linux for SHM creation

tools/utils/shm/fallocate_other.go

@@ -5,12 +5,12 @@
 package shm
 
 import (
+	"errors"
 	"fmt"
-	"golang.org/x/sys/unix"
 )
 
 var _ = fmt.Print
 
 func Fallocate_simple(fd int, size int64) (err error) {
-	return unix.ENOSYS
+	return errors.ErrUnsupported
 }

tools/utils/shm/shm.go

@@ -92,16 +92,15 @@ func CreateTemp(pattern string, size uint64) (MMap, error) {
 	return create_temp(pattern, size)
 }
 
-var force_use_of_fallocate bool = false
-
 func truncate_or_unlink(ans *os.File, size uint64) (err error) {
 	fd := int(ans.Fd())
-	if err = Fallocate_simple(fd, int64(size)); err != nil {
-		if force_use_of_fallocate {
+	sz := int64(size)
+	if err = Fallocate_simple(fd, sz); err != nil {
+		if !errors.Is(err, errors.ErrUnsupported) {
 			return err
 		}
 		for {
-			err = unix.Ftruncate(fd, int64(size))
+			err = unix.Ftruncate(fd, sz)
 			if !errors.Is(err, unix.EINTR) {
 				break
 			}

tools/utils/shm/shm_test.go

@@ -9,15 +9,12 @@ import (
 	"io/fs"
 	"os"
 	"reflect"
-	"runtime"
 	"testing"
 )
 
 var _ = fmt.Print
 
 func TestSHM(t *testing.T) {
-	force_use_of_fallocate = runtime.GOOS == "linux"
-	defer func() { force_use_of_fallocate = false }()
 	data := make([]byte, 13347)
 	_, _ = rand.Read(data)
 	mm, err := CreateTemp("test-kitty-shm-", uint64(len(data)))