btrfs: accept btrfs.size from storage.conf and apply default on RW layers

storage.conf documents [storage.options.btrfs] size, and pkg/config already
emits btrfs.size=... for the graph driver. The btrfs driver parseOptions
only handled min_space and rejected size, so storage init failed with an
unknown option error.
Parse size like min_space (RAMInBytes, enable quota when set). For
read-write layers, if there is no explicit storage-opt size, apply the
configured default inside create() without mutating the caller's
StorageOpt map and without formatting the default to a string only to
parse it again.
Add a small unit test for parseOptions.
Fixes: #718

Signed-off-by: Akhil Ammu <akhil.ammu@aiven.io>

Author: akhilsaivenkata

storage/drivers/btrfs/btrfs.go

@@ -114,6 +114,13 @@ func parseOptions(opt []string) (btrfsOptions, bool, error) {
 			}
 			userDiskQuota = true
 			options.minSpace = uint64(minSpace)
+		case "size":
+			size, err := units.RAMInBytes(val)
+			if err != nil {
+				return options, userDiskQuota, err
+			}
+			userDiskQuota = true
+			options.size = uint64(size)
 		case "mountopt":
 			return options, userDiskQuota, fmt.Errorf("btrfs driver does not support mount options")
 		default:
@@ -476,11 +483,20 @@ func (d *Driver) CreateFromTemplate(id, template string, templateIDMappings *idt
 // CreateReadWrite creates a layer that is writable for use as a container
 // file system.
 func (d *Driver) CreateReadWrite(id, parent string, opts *graphdriver.CreateOpts) error {
-	return d.Create(id, parent, opts)
+	var def *uint64
+	if d.options.size > 0 {
+		s := d.options.size
+		def = &s
+	}
+	return d.create(id, parent, opts, def)
 }
 
 // Create the filesystem with given id.
 func (d *Driver) Create(id, parent string, opts *graphdriver.CreateOpts) error {
+	return d.create(id, parent, opts, nil)
+}
+
+func (d *Driver) create(id, parent string, opts *graphdriver.CreateOpts, defaultSize *uint64) error {
 	quotas := d.quotasDir()
 	subvolumes := d.subvolumesDir()
 	if err := os.MkdirAll(subvolumes, 0o700); err != nil {
@@ -512,19 +528,31 @@ func (d *Driver) Create(id, parent string, opts *graphdriver.CreateOpts) error {
 		storageOpt = opts.StorageOpt
 	}
 
-	if _, ok := storageOpt["size"]; ok {
-		driver := &Driver{}
-		if err := d.parseStorageOpt(storageOpt, driver); err != nil {
-			return err
+	var quotaSize uint64
+	var needQuota bool
+	if storageOpt != nil {
+		if _, ok := storageOpt["size"]; ok {
+			driver := &Driver{}
+			if err := d.parseStorageOpt(storageOpt, driver); err != nil {
+				return err
+			}
+			quotaSize = driver.options.size
+			needQuota = true
 		}
-
-		if err := d.setStorageSize(path.Join(subvolumes, id), driver); err != nil {
+	}
+	if !needQuota && defaultSize != nil && *defaultSize > 0 {
+		quotaSize = *defaultSize
+		needQuota = true
+	}
+	if needQuota {
+		layerDriver := &Driver{options: btrfsOptions{size: quotaSize}}
+		if err := d.setStorageSize(path.Join(subvolumes, id), layerDriver); err != nil {
 			return err
 		}
 		if err := os.MkdirAll(quotas, 0o700); err != nil {
 			return err
 		}
-		if err := os.WriteFile(path.Join(quotas, id), []byte(fmt.Sprint(driver.options.size)), 0o644); err != nil {
+		if err := os.WriteFile(path.Join(quotas, id), []byte(fmt.Sprint(quotaSize)), 0o644); err != nil {
 			return err
 		}
 	}

storage/drivers/btrfs/btrfs_test.go

@@ -11,6 +11,16 @@ import (
 	"go.podman.io/storage/drivers/graphtest"
 )
 
+func TestParseOptionsBtrfsSize(t *testing.T) {
+	opts, wantQuota, err := parseOptions([]string{"btrfs.size=10m"})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !wantQuota || opts.size == 0 {
+		t.Fatalf("expected size and quota, got size=%d quota=%v", opts.size, wantQuota)
+	}
+}
+
 // This avoids creating a new driver for each test if all tests are run
 // Make sure to put new tests between TestBtrfsSetup and TestBtrfsTeardown
 func TestBtrfsSetup(t *testing.T) {