drivers, chown: support chown of hard links

make sure the same inode is not chowned twice.  Track all the inodes
that are chowned and skip the same inode if it is encountered multiple
times.

Closes: https://github.com/containers/storage/issues/1143

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

drivers/chown_unix.go

@@ -7,18 +7,27 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"sync"
 	"syscall"
 
 	"github.com/containers/storage/pkg/idtools"
 	"github.com/containers/storage/pkg/system"
 )
 
+type inode struct {
+	Dev uint64
+	Ino uint64
+}
 
 type platformChowner struct {
+	mutex  sync.Mutex
+	inodes map[inode]bool
 }
 
 func newLChowner() *platformChowner {
-	return &platformChowner{}
+	return &platformChowner{
+		inodes: make(map[inode]bool),
+	}
 }
 
 func (c *platformChowner) LChown(path string, info os.FileInfo, toHost, toContainer *idtools.IDMappings) error {
@@ -26,6 +35,22 @@ func (c *platformChowner) LChown(path string, info os.FileInfo, toHost, toContai
 	if !ok {
 		return nil
 	}
+
+	i := inode{
+		Dev: uint64(st.Dev),
+		Ino: uint64(st.Ino),
+	}
+	c.mutex.Lock()
+	_, found := c.inodes[i]
+	if !found {
+		c.inodes[i] = true
+	}
+	c.mutex.Unlock()
+
+	if found {
+		return nil
+	}
+
 	// Map an on-disk UID/GID pair from host to container
 	// using the first map, then back to the host using the
 	// second map.  Skip that first step if they're 0, to