fix: gc policy for windows to use 20% of disk space

cmd/buildkitd/config/gcpolicy.go

@@ -7,6 +7,7 @@ import (
 	"time"
 
 	"github.com/docker/go-units"
+	"github.com/moby/buildkit/util/bklog"
 	"github.com/pkg/errors"
 )
 
@@ -104,3 +105,25 @@ func stripQuotes(s string) string {
 	}
 	return s
 }
+
+func DetectDefaultGCCap() DiskSpace {
+	return DiskSpace{Percentage: DiskSpacePercentage}
+}
+
+func (d DiskSpace) AsBytes(root string) int64 {
+	if d.Bytes != 0 {
+		return d.Bytes
+	}
+	if d.Percentage == 0 {
+		return 0
+	}
+
+	diskSize, err := getDiskSize(root)
+	if err != nil {
+		bklog.L.Warnf("failed to get disk size: %v", err)
+		return defaultCap
+	}
+	avail := diskSize * d.Percentage / 100
+	rounded := (avail/(1<<30) + 1) * 1e9 // round up
+	return rounded
+}

cmd/buildkitd/config/gcpolicy_unix.go

@@ -7,23 +7,13 @@ import (
 	"syscall"
 )
 
-func DetectDefaultGCCap() DiskSpace {
-	return DiskSpace{Percentage: 10}
-}
-
-func (d DiskSpace) AsBytes(root string) int64 {
-	if d.Bytes != 0 {
-		return d.Bytes
-	}
-	if d.Percentage == 0 {
-		return 0
-	}
+var DiskSpacePercentage int64 = 10
 
+func getDiskSize(root string) (int64, error) {
 	var st syscall.Statfs_t
 	if err := syscall.Statfs(root, &st); err != nil {
-		return defaultCap
+		return 0, err
 	}
 	diskSize := int64(st.Bsize) * int64(st.Blocks)
-	avail := diskSize * d.Percentage / 100
-	return (avail/(1<<30) + 1) * 1e9 // round up
+	return diskSize, nil
 }

cmd/buildkitd/config/gcpolicy_windows.go

@@ -3,10 +3,29 @@
 
 package config
 
-func DetectDefaultGCCap() DiskSpace {
-	return DiskSpace{Bytes: defaultCap}
-}
+import (
+	"golang.org/x/sys/windows"
+)
+
+// set as double that for Linux since
+// Windows images are generally larger.
+var DiskSpacePercentage int64 = 20
+
+func getDiskSize(root string) (int64, error) {
+	rootUTF16, err := windows.UTF16FromString(root)
+	if err != nil {
+		return 0, err
+	}
+	var freeAvailableBytes uint64
+	var totalBytes uint64
+	var totalFreeBytes uint64
 
-func (d DiskSpace) AsBytes(root string) int64 {
-	return d.Bytes
+	if err := windows.GetDiskFreeSpaceEx(
+		&rootUTF16[0],
+		&freeAvailableBytes,
+		&totalBytes,
+		&totalFreeBytes); err != nil {
+		return 0, err
+	}
+	return int64(totalBytes), nil
 }