volume: use FALLOC_FL_KEEP_SIZE and log preallocation failures (#11920)

weed/storage/backend/volume_create_linux.go

@@ -4,7 +4,8 @@ package backend
 
 import (
 	"os"
-	"syscall"
+
+	"golang.org/x/sys/unix"
 
 	"github.com/seaweedfs/seaweedfs/weed/glog"
 )
@@ -15,8 +16,11 @@ func CreateVolumeFile(fileName string, preallocate int64, memoryMapSizeMB uint32
 		return nil, e
 	}
 	if preallocate != 0 {
-		syscall.Fallocate(int(file.Fd()), 1, 0, preallocate)
-		glog.V(1).Infof("Preallocated %d bytes disk space for %s", preallocate, fileName)
+		if err := unix.Fallocate(int(file.Fd()), unix.FALLOC_FL_KEEP_SIZE, 0, preallocate); err != nil {
+			glog.Warningf("Preallocate %d bytes disk space for %s: %v", preallocate, fileName, err)
+		} else {
+			glog.V(1).Infof("Preallocated %d bytes disk space for %s", preallocate, fileName)
+		}
 	}
 	return NewDiskFile(file), nil
 }

weed/storage/backend/volume_create_linux_test.go

@@ -0,0 +1,50 @@
+//go:build linux
+
+package backend
+
+import (
+	"os"
+	"path/filepath"
+	"syscall"
+	"testing"
+
+	"golang.org/x/sys/unix"
+)
+
+func TestCreateVolumeFilePreallocateKeepsSize(t *testing.T) {
+	dir := t.TempDir()
+	const preallocate = 1 << 20
+
+	probe, err := os.Create(filepath.Join(dir, "probe"))
+	if err != nil {
+		t.Fatalf("create probe: %v", err)
+	}
+	err = unix.Fallocate(int(probe.Fd()), unix.FALLOC_FL_KEEP_SIZE, 0, preallocate)
+	probe.Close()
+	if err != nil {
+		t.Skipf("fallocate not supported in %s: %v", dir, err)
+	}
+
+	fileName := filepath.Join(dir, "1.dat")
+	f, err := CreateVolumeFile(fileName, preallocate, 0)
+	if err != nil {
+		t.Fatalf("CreateVolumeFile: %v", err)
+	}
+	defer f.Close()
+
+	size, _, err := f.GetStat()
+	if err != nil {
+		t.Fatalf("GetStat: %v", err)
+	}
+	if size != 0 {
+		t.Errorf("file size = %d, want 0", size)
+	}
+
+	var st syscall.Stat_t
+	if err := syscall.Stat(fileName, &st); err != nil {
+		t.Fatalf("stat: %v", err)
+	}
+	if st.Blocks*512 < preallocate {
+		t.Errorf("allocated %d bytes, want at least %d", st.Blocks*512, preallocate)
+	}
+}