Added cow option to bind

The option cow can now be set for files which are then
mounted during exec, but copied into the image and removed
if not modified.

Signed-off-by: Christian Goll <cgoll@suse.com>

CHANGELOG.md

@@ -46,6 +46,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 - Added option for wwclient port number. #1349
 - Additional helper directions during syncuser conflict. #1359
+- Add `:cow` suffix to `wwctl container exec --bind` to temporarily copy files into the node image. #1365
 
 ### Changed
 

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)

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.Info("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
+}

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")
 }

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")
 }
 

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
 }

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)
 	}

userdocs/contents/containers.rst

@@ -213,6 +213,21 @@ 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.