warewulf4/added-cow-option-to-bind.patch

diff --git a/internal/app/wwctl/container/exec/child/main.go b/internal/app/wwctl/container/exec/child/main.go
index 253a6ad2..ba9ad9f7 100644
--- a/internal/app/wwctl/container/exec/child/main.go
+++ b/internal/app/wwctl/container/exec/child/main.go
@@ -92,7 +92,7 @@ func CobraRunE(cmd *cobra.Command, args []string) (err error) {
 		wwlog.Debug("overlay options: %s", options)
 		err = syscall.Mount("overlay", containerPath, "overlay", 0, options)
 		if err != nil {
-			wwlog.Warn(fmt.Sprintf("Couldn't create overlay for ephermal mount points: %s", err))
+			wwlog.Warn("Couldn't create overlay for ephermal mount points: %s", err)
 		}
 	} else if nodename != "" {
 		nodeDB, err := node.New()
@@ -142,6 +142,10 @@ func CobraRunE(cmd *cobra.Command, args []string) (err error) {
 	}
 
 	for _, mntPnt := range mountPts {
+		if mntPnt.Cow {
+			continue
+		}
+		wwlog.Debug("bind mounting: %s -> %s", mntPnt.Source, path.Join(containerPath, mntPnt.Dest))
 		err = syscall.Mount(mntPnt.Source, path.Join(containerPath, mntPnt.Dest), "", syscall.MS_BIND, "")
 		if err != nil {
 			wwlog.Warn("Couldn't mount %s to %s: %s", mntPnt.Source, mntPnt.Dest, err)
@@ -195,6 +199,9 @@ the invalid mount points. Directories always have '/' as suffix
 func checkMountPoints(containerName string, binds []*warewulfconf.MountEntry) (overlayObjects []string) {
 	overlayObjects = []string{}
 	for _, b := range binds {
+		if b.Cow {
+			continue
+		}
 		_, err := os.Stat(b.Source)
 		if err != nil {
 			wwlog.Debug("Couldn't stat %s create no mount point in container", b.Source)
diff --git a/internal/app/wwctl/container/exec/main.go b/internal/app/wwctl/container/exec/main.go
index 60cf9d48..788adc86 100644
--- a/internal/app/wwctl/container/exec/main.go
+++ b/internal/app/wwctl/container/exec/main.go
@@ -54,7 +54,6 @@ func runContainedCmd(cmd *cobra.Command, containerName string, args []string) (e
 	}()
 
 	logStr := fmt.Sprint(wwlog.GetLogLevel())
-
 	childArgs := []string{"--warewulfconf", conf.GetWarewulfConf(), "--loglevel", logStr, "container", "exec", "__child"}
 	childArgs = append(childArgs, containerName)
 	for _, b := range binds {
@@ -64,8 +63,40 @@ func runContainedCmd(cmd *cobra.Command, containerName string, args []string) (e
 		childArgs = append(childArgs, "--node", nodeName)
 	}
 	childArgs = append(childArgs, args...)
+	// copy the files into the container at this stage, es in __child the
+	// command syscall.Exec which replaces the __child process with the
+	// exec command in the container. All the mounts, have to be done in
+	// __child so that the used mounts don't propagate outside on the host
+	// (see the CLONE attributes), but as for the cow copy option we need
+	// to see if a file was modified after it was copied into the container
+	// so do this here.
+	// At first read out conf, the parse commandline, as copy files has the
+	// same synatx as mount points
+	mountPts := conf.MountsContainer
+	mountPts = append(container.InitMountPnts(binds), mountPts...)
+	filesToCpy := getCopyFiles(containerName, mountPts)
+	for i, cpyFile := range filesToCpy {
+		if err = util.CopyFile(cpyFile.Src, path.Join(container.RootFsDir(containerName), cpyFile.FileName)); err != nil {
+			return fmt.Errorf("couldn't copy files into container: %w", err)
+		}
+		// we can ignore error as the file was copied
+		stat, _ := os.Stat(path.Join(container.RootFsDir(containerName), cpyFile.FileName))
+		filesToCpy[i].ModTime = stat.ModTime()
+	}
 	wwlog.Verbose("Running contained command: %s", childArgs)
-	return childCommandFunc(cmd, childArgs)
+	retVal := childCommandFunc(cmd, childArgs)
+	for _, cpyFile := range filesToCpy {
+		if modStat, err := os.Stat(path.Join(container.RootFsDir(containerName), cpyFile.FileName)); err != nil {
+			wwlog.Warn("copied file was removed: %s", err)
+		} else {
+			if modStat.ModTime() == cpyFile.ModTime {
+				if err := os.Remove(path.Join(container.RootFsDir(containerName), cpyFile.FileName)); err != nil {
+					wwlog.Warn("couldn't remove copied file: %s", err)
+				}
+			}
+		}
+	}
+	return retVal
 }
 
 func CobraRunE(cmd *cobra.Command, args []string) error {
@@ -154,3 +185,40 @@ func SetBinds(myBinds []string) {
 func SetNode(myNode string) {
 	nodeName = myNode
 }
+
+// file name and last modification time so we can remove the file if it wasn't modified
+type cowFile struct {
+	FileName string
+	Src      string
+	ModTime  time.Time
+	Cow      bool
+}
+
+/*
+Check the objects we want to copy in, instead of mounting
+*/
+func getCopyFiles(containerNamer string, binds []*warewulfconf.MountEntry) (copyObjects []cowFile) {
+	for _, bind := range binds {
+		if !bind.Cow || bind.ReadOnly {
+			continue
+		}
+		if _, err := os.Stat(path.Join(container.RootFsDir(containerNamer), path.Dir(bind.Dest))); err != nil {
+			wwlog.Warn("destination directory doesn't exist: %s", err)
+			continue
+		}
+		if _, err := os.Stat(path.Join(container.RootFsDir(containerNamer), bind.Dest)); err == nil {
+			wwlog.Verbose("file exists in container: %s", bind.Dest)
+			continue
+		}
+		if _, err := os.Stat(bind.Source); err != nil {
+			wwlog.Warn("source doesn't exist: %s", err)
+			continue
+		}
+		copyObjects = append(copyObjects, cowFile{
+			FileName: bind.Dest,
+			Src:      bind.Source,
+			Cow:      bind.Cow,
+		})
+	}
+	return
+}
diff --git a/internal/app/wwctl/container/exec/root.go b/internal/app/wwctl/container/exec/root.go
index 4b74c941..0b6aaf63 100644
--- a/internal/app/wwctl/container/exec/root.go
+++ b/internal/app/wwctl/container/exec/root.go
@@ -32,7 +32,11 @@ var (
 
 func init() {
 	baseCmd.AddCommand(child.GetCommand())
-	baseCmd.PersistentFlags().StringArrayVarP(&binds, "bind", "b", []string{}, "Bind a local path into the container (must exist)")
+	baseCmd.PersistentFlags().StringArrayVarP(&binds, "bind", "b", []string{}, `Bind a local path which must exist into the container. Syntax is
+source[:destination[:{ro|cow}]] If destination is not set, 
+it will the same path as source.The additional parameter is 
+ro for read only and cow, which means the file is copied into 
+the container and removed if not modified.`)
 	baseCmd.PersistentFlags().BoolVar(&SyncUser, "syncuser", false, "Synchronize UIDs/GIDs from host to container")
 	baseCmd.PersistentFlags().StringVarP(&nodeName, "node", "n", "", "Create a read only view of the container for the given node")
 }
diff --git a/internal/app/wwctl/container/shell/root.go b/internal/app/wwctl/container/shell/root.go
index cceb7512..52d9825d 100644
--- a/internal/app/wwctl/container/shell/root.go
+++ b/internal/app/wwctl/container/shell/root.go
@@ -28,7 +28,11 @@ var (
 )
 
 func init() {
-	baseCmd.PersistentFlags().StringArrayVarP(&binds, "bind", "b", []string{}, "Bind a local path into the container (must exist)")
+	baseCmd.PersistentFlags().StringArrayVarP(&binds, "bind", "b", []string{}, `Bind a local path which must exist into the container. Syntax is
+source[:destination[:{ro|cow}]] If destination is not set, 
+it will the same path as source.The additional parameter is 
+ro for read only and cow, which means the file is copied into 
+the container and removed if not modified.`)
 	baseCmd.PersistentFlags().StringVarP(&nodeName, "node", "n", "", "Create a read only view of the container for the given node")
 }
 
diff --git a/internal/pkg/config/mounts.go b/internal/pkg/config/mounts.go
index 2eb5060b..35805202 100644
--- a/internal/pkg/config/mounts.go
+++ b/internal/pkg/config/mounts.go
@@ -7,4 +7,5 @@ type MountEntry struct {
 	Dest     string `yaml:"dest,omitempty"`
 	ReadOnly bool   `yaml:"readonly,omitempty"`
 	Options  string `yaml:"options,omitempty"` // ignored at the moment
+	Cow      bool   `yaml:"cow,omitempty"`     // copy the file into the container and don't remove if modified
 }
diff --git a/internal/pkg/container/mountpoints.go b/internal/pkg/container/mountpoints.go
index 5de00c75..7c16a0a9 100644
--- a/internal/pkg/container/mountpoints.go
+++ b/internal/pkg/container/mountpoints.go
@@ -21,13 +21,19 @@ func InitMountPnts(binds []string) (mounts []*warewulfconf.MountEntry) {
 			dest = bind[1]
 		}
 		readonly := false
-		if len(bind) >= 3 && bind[2] == "ro" {
-			readonly = true
+		cow := false
+		if len(bind) >= 3 {
+			if bind[2] == "ro" {
+				readonly = true
+			} else if bind[2] == "cow" {
+				cow = true
+			}
 		}
 		mntPnt := warewulfconf.MountEntry{
 			Source:   bind[0],
 			Dest:     dest,
 			ReadOnly: readonly,
+			Cow:      cow,
 		}
 		mounts = append(mounts, &mntPnt)
 	}
diff --git a/userdocs/contents/containers.rst b/userdocs/contents/containers.rst
index aa8385eb..02e0fbc6 100644
--- a/userdocs/contents/containers.rst
+++ b/userdocs/contents/containers.rst
@@ -216,6 +216,21 @@ when using the exec command. This works as follows:
    location, as it is almost always present and empty in every Linux
    distribution (as prescribed by the LSB file hierarchy standard).
 
+Files which should always be present in a container image like ``resolv.conf``
+can be specified in ``warewulf.conf`` with following container_exit
+
+.. code-block:: yaml
+   container mounts:
+   - source: /etc/resolv.conf
+     dest: /etc/resolv.conf
+     readonly: true
+
+.. note::
+   Instead of the ``readonly`` setting you can set ``cow``, which 
+   has the effect, that the source file is copied to the container
+   and removed if it was modified. This useful for file used for
+   registrations.
+
 When the command completes, if anything within the container changed,
 the container will be rebuilt into a bootable static object
 automatically.