daemon/graphdriver: simplify Checker, remove NewFsChecker, NewDefaultChecker

The Checker interface was introduced in 1ba05cdb6a
as an optimization to allow passing a simplified check for situations that
don't require mountinfo.Mounted to be executed (as that may result in parsing
 `/proc/self/mountinfo`).

The Checker was defined as an interface with a single `IsMounted` method,
possibly with the intent to allow for additional kind of checks to be added.
No new additions were made since its inception 9 Years ago, and if a need would
arrive, could probably be implemented as part of the check.

This patch simplifies the definition to a function, removing the need to
implement a wrapper struct just to satisfy the interface. The `Checker`
type definition is somewhat redundant, but is kept to have a place to
provide GoDoc.

The `NewFsChecker` and `NewDefaultChecker` utilities are removed as part
of this change, favoring a local definition for storage-drivers that
used them.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

daemon/graphdriver/counter.go

@@ -9,16 +9,20 @@ type minfo struct {
 
 // RefCounter is a generic counter for use by graphdriver Get/Put calls
 type RefCounter struct {
-	counts  map[string]*minfo
-	mu      sync.Mutex
-	checker Checker
+	counts    map[string]*minfo
+	mu        sync.Mutex
+	isMounted Checker
 }
 
-// NewRefCounter returns a new RefCounter
+// Checker checks whether the provided path is mounted.
+type Checker func(path string) bool
+
+// NewRefCounter returns a new RefCounter. It accepts a [Checker] to
+// determine whether a path is mounted.
 func NewRefCounter(c Checker) *RefCounter {
 	return &RefCounter{
-		checker: c,
-		counts:  make(map[string]*minfo),
+		isMounted: c,
+		counts:    make(map[string]*minfo),
 	}
 }
 
@@ -48,7 +52,7 @@ func (c *RefCounter) incdec(path string, infoOp func(minfo *minfo)) int {
 	// count if it is mounted as it is in use.
 	if !m.check {
 		m.check = true
-		if c.checker.IsMounted(path) {
+		if c.isMounted(path) {
 			m.count++
 		}
 	}

daemon/graphdriver/driver.go

@@ -128,12 +128,6 @@ type FileGetCloser interface {
 	Close() error
 }
 
-// Checker makes checks on specified filesystems.
-type Checker interface {
-	// IsMounted returns true if the provided path is mounted for the specific checker
-	IsMounted(path string) bool
-}
-
 func init() {
 	drivers = make(map[string]InitFunc)
 }

daemon/graphdriver/driver_linux.go

@@ -1,38 +1,4 @@
 package graphdriver // import "github.com/docker/docker/daemon/graphdriver"
 
-import (
-	"github.com/docker/docker/daemon/internal/fstype"
-	"github.com/moby/sys/mountinfo"
-)
-
 // List of drivers that should be used in an order
 var priority = "overlay2,fuse-overlayfs,btrfs,zfs,vfs"
-
-// NewFsChecker returns a checker configured for the provided FsMagic
-func NewFsChecker(t fstype.FsMagic) Checker {
-	return &fsChecker{
-		t: t,
-	}
-}
-
-type fsChecker struct {
-	t fstype.FsMagic
-}
-
-func (c *fsChecker) IsMounted(path string) bool {
-	fsType, _ := fstype.GetFSMagic(path)
-	return fsType == c.t
-}
-
-// NewDefaultChecker returns a check that parses /proc/mountinfo to check
-// if the specified path is mounted.
-func NewDefaultChecker() Checker {
-	return &defaultChecker{}
-}
-
-type defaultChecker struct{}
-
-func (c *defaultChecker) IsMounted(path string) bool {
-	m, _ := mountinfo.Mounted(path)
-	return m
-}

daemon/graphdriver/fuse-overlayfs/fuseoverlayfs.go

@@ -98,7 +98,7 @@ func Init(home string, options []string, idMap idtools.IdentityMapping) (graphdr
 	d := &Driver{
 		home:   home,
 		idMap:  idMap,
-		ctr:    graphdriver.NewRefCounter(graphdriver.NewFsChecker(fstype.FsMagicFUSE)),
+		ctr:    graphdriver.NewRefCounter(isMounted),
 		locker: locker.New(),
 	}
 
@@ -107,6 +107,12 @@ func Init(home string, options []string, idMap idtools.IdentityMapping) (graphdr
 	return d, nil
 }
 
+// isMounted checks whether the given path is a [fstype.FsMagicFUSE] mount.
+func isMounted(path string) bool {
+	fsType, _ := fstype.GetFSMagic(path)
+	return fsType == fstype.FsMagicFUSE
+}
+
 func (d *Driver) String() string {
 	return driverName
 }

daemon/graphdriver/overlay2/overlay.go

@@ -179,7 +179,7 @@ func Init(home string, options []string, idMap idtools.IdentityMapping) (graphdr
 	d := &Driver{
 		home:          home,
 		idMap:         idMap,
-		ctr:           graphdriver.NewRefCounter(graphdriver.NewFsChecker(fstype.FsMagicOverlay)),
+		ctr:           graphdriver.NewRefCounter(isMounted),
 		supportsDType: supportsDType,
 		usingMetacopy: usingMetacopy,
 		locker:        locker.New(),
@@ -225,6 +225,12 @@ func Init(home string, options []string, idMap idtools.IdentityMapping) (graphdr
 	return d, nil
 }
 
+// isMounted checks whether the given path is a [fstype.FsMagicOverlay] mount.
+func isMounted(path string) bool {
+	fsType, _ := fstype.GetFSMagic(path)
+	return fsType == fstype.FsMagicOverlay
+}
+
 func parseOptions(options []string) (*overlayOptions, error) {
 	o := &overlayOptions{}
 	for _, option := range options {

daemon/graphdriver/windows/windows.go

@@ -72,12 +72,6 @@ func init() {
 	}
 }
 
-type checker struct{}
-
-func (c *checker) IsMounted(path string) bool {
-	return false
-}
-
 type storageOptions struct {
 	size uint64
 }
@@ -132,12 +126,18 @@ func InitFilter(home string, options []string, _ idtools.IdentityMapping) (graph
 			Flavour: filterDriver,
 		},
 		cache:              make(map[string]string),
-		ctr:                graphdriver.NewRefCounter(&checker{}),
+		ctr:                graphdriver.NewRefCounter(isMounted),
 		defaultStorageOpts: opts,
 	}
 	return d, nil
 }
 
+// isMounted checks whether the given path is mounted. It always returns
+// false for the WindowsFilter graphdriver.
+func isMounted(string) bool {
+	return false
+}
+
 // String returns the string representation of a driver. This should match
 // the name the graph driver has been registered with.
 func (d *Driver) String() string {

daemon/graphdriver/zfs/zfs.go

@@ -118,12 +118,19 @@ func Init(base string, opt []string, idMap idtools.IdentityMapping) (graphdriver
 		options:          options,
 		filesystemsCache: filesystemsCache,
 		idMap:            idMap,
-		ctr:              graphdriver.NewRefCounter(graphdriver.NewDefaultChecker()),
+		ctr:              graphdriver.NewRefCounter(isMounted),
 		locker:           locker.New(),
 	}
 	return graphdriver.NewNaiveDiffDriver(d, idMap), nil
 }
 
+// isMounted parses /proc/mountinfo to check whether the specified path
+// is mounted.
+func isMounted(path string) bool {
+	m, _ := mountinfo.Mounted(path)
+	return m
+}
+
 func parseOptions(opt []string) (zfsOptions, error) {
 	var options zfsOptions
 	options.fsName = ""