Simplify/fix MkdirAll usage

This subtle bug keeps lurking in because error checking for `Mkdir()`
and `MkdirAll()` is slightly different wrt to `EEXIST`/`IsExist`:

 - for `Mkdir()`, `IsExist` error should (usually) be ignored
   (unless you want to make sure directory was not there before)
   as it means "the destination directory was already there"

 - for `MkdirAll()`, `IsExist` error should NEVER be ignored.

Mostly, this commit just removes ignoring the IsExist error, as it
should not be ignored.

Also, there are a couple of cases then IsExist is handled as
"directory already exist" which is wrong. As a result, some code
that never worked as intended is now removed.

NOTE that `idtools.MkdirAndChown()` behaves like `os.MkdirAll()`
rather than `os.Mkdir()` -- so its description is amended accordingly,
and its usage is handled as such (i.e. IsExist error is not ignored).

For more details, a quote from my runc commit 6f82d4b (July 2015):

    TL;DR: check for IsExist(err) after a failed MkdirAll() is both
    redundant and wrong -- so two reasons to remove it.

    Quoting MkdirAll documentation:

    > MkdirAll creates a directory named path, along with any necessary
    > parents, and returns nil, or else returns an error. If path
    > is already a directory, MkdirAll does nothing and returns nil.

    This means two things:

    1. If a directory to be created already exists, no error is
    returned.

    2. If the error returned is IsExist (EEXIST), it means there exists
    a non-directory with the same name as MkdirAll need to use for
    directory. Example: we want to MkdirAll("a/b"), but file "a"
    (or "a/b") already exists, so MkdirAll fails.

    The above is a theory, based on quoted documentation and my UNIX
    knowledge.

    3. In practice, though, current MkdirAll implementation [1] returns
    ENOTDIR in most of cases described in #2, with the exception when
    there is a race between MkdirAll and someone else creating the
    last component of MkdirAll argument as a file. In this very case
    MkdirAll() will indeed return EEXIST.

    Because of #1, IsExist check after MkdirAll is not needed.

    Because of #2 and #3, ignoring IsExist error is just plain wrong,
    as directory we require is not created. It's cleaner to report
    the error now.

    Note this error is all over the tree, I guess due to copy-paste,
    or trying to follow the same usage pattern as for Mkdir(),
    or some not quite correct examples on the Internet.

    [1] https://github.com/golang/go/blob/f9ed2f75/src/os/path.go

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

Author: kolyshkin

daemon/checkpoint.go

@@ -34,9 +34,6 @@ func getCheckpointDir(checkDir, checkpointID, ctrName, ctrID, ctrCheckpointDir s
 			err2 = fmt.Errorf("checkpoint with name %s already exists for container %s", checkpointID, ctrName)
 		case err != nil && os.IsNotExist(err):
 			err2 = os.MkdirAll(checkpointAbsDir, 0700)
-			if os.IsExist(err2) {
-				err2 = nil
-			}
 		case err != nil:
 			err2 = err
 		case err == nil:

daemon/daemon.go

@@ -675,22 +675,22 @@ func NewDaemon(config *config.Config, registryService registry.Service, containe
 	}
 
 	daemonRepo := filepath.Join(config.Root, "containers")
-	if err := idtools.MkdirAllAndChown(daemonRepo, 0700, rootIDs); err != nil && !os.IsExist(err) {
+	if err := idtools.MkdirAllAndChown(daemonRepo, 0700, rootIDs); err != nil {
 		return nil, err
 	}
 
 	// Create the directory where we'll store the runtime scripts (i.e. in
 	// order to support runtimeArgs)
 	daemonRuntimes := filepath.Join(config.Root, "runtimes")
-	if err := system.MkdirAll(daemonRuntimes, 0700, ""); err != nil && !os.IsExist(err) {
+	if err := system.MkdirAll(daemonRuntimes, 0700, ""); err != nil {
 		return nil, err
 	}
 	if err := d.loadRuntimes(); err != nil {
 		return nil, err
 	}
 
 	if runtime.GOOS == "windows" {
-		if err := system.MkdirAll(filepath.Join(config.Root, "credentialspecs"), 0, ""); err != nil && !os.IsExist(err) {
+		if err := system.MkdirAll(filepath.Join(config.Root, "credentialspecs"), 0, ""); err != nil {
 			return nil, err
 		}
 	}

daemon/daemon_unix.go

@@ -1514,7 +1514,7 @@ func (daemon *Daemon) initCgroupsPath(path string) error {
 
 func maybeCreateCPURealTimeFile(sysinfoPresent bool, configValue int64, file string, path string) error {
 	if sysinfoPresent && configValue != 0 {
-		if err := os.MkdirAll(path, 0755); err != nil && !os.IsExist(err) {
+		if err := os.MkdirAll(path, 0755); err != nil {
 			return err
 		}
 		if err := ioutil.WriteFile(filepath.Join(path, file), []byte(strconv.FormatInt(configValue, 10)), 0700); err != nil {

daemon/daemon_windows.go

@@ -3,7 +3,6 @@ package daemon
 import (
 	"context"
 	"fmt"
-	"os"
 	"path/filepath"
 	"strings"
 
@@ -485,7 +484,7 @@ func setupRemappedRoot(config *config.Config) (*idtools.IDMappings, error) {
 func setupDaemonRoot(config *config.Config, rootDir string, rootIDs idtools.IDPair) error {
 	config.Root = rootDir
 	// Create the root directory if it doesn't exists
-	if err := system.MkdirAllWithACL(config.Root, 0, system.SddlAdministratorsLocalSystem); err != nil && !os.IsExist(err) {
+	if err := system.MkdirAllWithACL(config.Root, 0, system.SddlAdministratorsLocalSystem); err != nil {
 		return err
 	}
 	return nil

daemon/graphdriver/aufs/aufs.go

@@ -122,13 +122,8 @@ func Init(root string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap
 	if err != nil {
 		return nil, err
 	}
-	// Create the root aufs driver dir and return
-	// if it already exists
-	// If not populate the dir structure
+	// Create the root aufs driver dir
 	if err := idtools.MkdirAllAndChown(root, 0700, idtools.IDPair{UID: rootUID, GID: rootGID}); err != nil {
-		if os.IsExist(err) {
-			return a, nil
-		}
 		return nil, err
 	}
 

daemon/graphdriver/devmapper/deviceset.go

@@ -268,7 +268,7 @@ func (devices *DeviceSet) ensureImage(name string, size int64) (string, error) {
 	if err != nil {
 		return "", err
 	}
-	if err := idtools.MkdirAllAndChown(dirname, 0700, idtools.IDPair{UID: uid, GID: gid}); err != nil && !os.IsExist(err) {
+	if err := idtools.MkdirAllAndChown(dirname, 0700, idtools.IDPair{UID: uid, GID: gid}); err != nil {
 		return "", err
 	}
 
@@ -1697,10 +1697,10 @@ func (devices *DeviceSet) initDevmapper(doInit bool) (retErr error) {
 	if err != nil {
 		return err
 	}
-	if err := idtools.MkdirAndChown(devices.root, 0700, idtools.IDPair{UID: uid, GID: gid}); err != nil && !os.IsExist(err) {
+	if err := idtools.MkdirAndChown(devices.root, 0700, idtools.IDPair{UID: uid, GID: gid}); err != nil {
 		return err
 	}
-	if err := os.MkdirAll(devices.metadataDir(), 0700); err != nil && !os.IsExist(err) {
+	if err := os.MkdirAll(devices.metadataDir(), 0700); err != nil {
 		return err
 	}
 

daemon/graphdriver/devmapper/driver.go

@@ -189,7 +189,7 @@ func (d *Driver) Get(id, mountLabel string) (containerfs.ContainerFS, error) {
 	}
 
 	// Create the target directories if they don't exist
-	if err := idtools.MkdirAllAndChown(path.Join(d.home, "mnt"), 0755, idtools.IDPair{UID: uid, GID: gid}); err != nil && !os.IsExist(err) {
+	if err := idtools.MkdirAllAndChown(path.Join(d.home, "mnt"), 0755, idtools.IDPair{UID: uid, GID: gid}); err != nil {
 		d.ctr.Decrement(mp)
 		return nil, err
 	}
@@ -204,7 +204,7 @@ func (d *Driver) Get(id, mountLabel string) (containerfs.ContainerFS, error) {
 		return nil, err
 	}
 
-	if err := idtools.MkdirAllAndChown(rootFs, 0755, idtools.IDPair{UID: uid, GID: gid}); err != nil && !os.IsExist(err) {
+	if err := idtools.MkdirAllAndChown(rootFs, 0755, idtools.IDPair{UID: uid, GID: gid}); err != nil {
 		d.ctr.Decrement(mp)
 		d.DeviceSet.UnmountDevice(id, mp)
 		return nil, err

daemon/graphdriver/overlay/overlay.go

@@ -136,7 +136,7 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap
 		return nil, err
 	}
 	// Create the driver home dir
-	if err := idtools.MkdirAllAndChown(home, 0700, idtools.IDPair{rootUID, rootGID}); err != nil && !os.IsExist(err) {
+	if err := idtools.MkdirAllAndChown(home, 0700, idtools.IDPair{rootUID, rootGID}); err != nil {
 		return nil, err
 	}
 

daemon/graphdriver/overlay2/overlay.go

@@ -171,7 +171,7 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap
 		return nil, err
 	}
 	// Create the driver home dir
-	if err := idtools.MkdirAllAndChown(path.Join(home, linkDir), 0700, idtools.IDPair{rootUID, rootGID}); err != nil && !os.IsExist(err) {
+	if err := idtools.MkdirAllAndChown(path.Join(home, linkDir), 0700, idtools.IDPair{rootUID, rootGID}); err != nil {
 		return nil, err
 	}
 

pkg/idtools/idtools.go

@@ -42,7 +42,9 @@ func MkdirAllAndChown(path string, mode os.FileMode, owner IDPair) error {
 }
 
 // MkdirAndChown creates a directory and then modifies ownership to the requested uid/gid.
-// If the directory already exists, this function still changes ownership
+// If the directory already exists, this function still changes ownership.
+// Note that unlike os.Mkdir(), this function does not return IsExist error
+// in case path already exists.
 func MkdirAndChown(path string, mode os.FileMode, owner IDPair) error {
 	return mkdirAs(path, mode, owner.UID, owner.GID, false, true)
 }