Merge pull request #1365 from mslacken/CopyOnChange

add cow option for binds

CHANGELOG.md

@@ -46,6 +46,8 @@ 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
+- Add `:copy` 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.Copy {
+			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.Copy {
+			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 +63,32 @@ 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 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 := append(container.InitMountPnts(binds), conf.MountsContainer...)
+	filesToCpy := getCopyFiles(mountPts)
+	for _, cpyFile := range filesToCpy {
+		if err := (cpyFile).copyToContainer(containerName); err != nil {
+			wwlog.Warn("couldn't copy file: %s", err)
+		}
+	}
 	wwlog.Verbose("Running contained command: %s", childArgs)
-	return childCommandFunc(cmd, childArgs)
+	retVal := childCommandFunc(cmd, childArgs)
+	for _, cpyFile := range filesToCpy {
+		if cpyFile.shouldRemoveFromContainer(containerName) {
+			if err := cpyFile.removeFromContainer(containerName); err != nil {
+				wwlog.Warn("couldn't remove file: %s", err)
+			}
+		}
+	}
+	return retVal
 }
 
 func CobraRunE(cmd *cobra.Command, args []string) error {
@@ -154,3 +177,68 @@ 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 copyFile struct {
+	fileName string
+	src      string
+	modTime  time.Time
+}
+
+func (this *copyFile) containerDest(containerName string) string {
+	return path.Join(container.RootFsDir(containerName), this.fileName)
+}
+
+func (this *copyFile) copyToContainer(containerName string) error {
+	containerDest := this.containerDest(containerName)
+	if _, err := os.Stat(path.Dir(containerDest)); err != nil {
+		return err
+	} else if _, err := os.Stat(containerDest); err == nil {
+		return err
+	} else if _, err := os.Stat(this.src); err != nil {
+		return err
+	} else if err := util.CopyFile(this.src, containerDest); err != nil {
+		return err
+	} else if stat, err := os.Stat(containerDest); err != nil {
+		return err
+	} else {
+		this.modTime = stat.ModTime()
+		return nil
+	}
+}
+
+func (this *copyFile) shouldRemoveFromContainer(containerName string) bool {
+	containerDest := this.containerDest(containerName)
+	if this.modTime.IsZero() {
+		wwlog.Debug("file was not previously copied: %s", this.fileName)
+		return false
+	} else if destStat, err := os.Stat(containerDest); err != nil {
+		wwlog.Verbose("file is no longer present: %s (%s)", this.fileName, err)
+		return false
+	} else if destStat.ModTime() == this.modTime {
+		wwlog.Verbose("don't remove modified file:", this.fileName)
+		return false
+	} else {
+		return true
+	}
+}
+
+func (this *copyFile) removeFromContainer(containerName string) error {
+	containerDest := this.containerDest(containerName)
+	return os.Remove(containerDest)
+}
+
+/*
+Check the objects we want to copy in, instead of mounting
+*/
+func getCopyFiles(binds []*warewulfconf.MountEntry) (copyObjects []*copyFile) {
+	for _, bind := range binds {
+		if bind.Copy {
+			copyObjects = append(copyObjects, &copyFile{
+				fileName: bind.Dest,
+				src:      bind.Source,
+			})
+		}
+	}
+	return
+}

internal/app/wwctl/container/exec/root.go

@@ -32,7 +32,10 @@ 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{}, `source[:destination[:{ro|copy}]]
+Bind a local path which must exist into the container. If destination is not
+set, uses the same path as source. "ro" binds read-only. "copy" temporarily
+copies the file into the container.`)
 	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 +28,10 @@ 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{}, `source[:destination[:{ro|copy}]]
+Bind a local path which must exist into the container. If destination is not
+set, uses the same path as source. "ro" binds read-only. "copy" temporarily
+copies the file into the container.`)
 	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
+	Copy     bool   `yaml:"copy,omitempty"`    // temporarily copy the file into the container
 }

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
+		copy_ := false
+		if len(bind) >= 3 {
+			if bind[2] == "ro" {
+				readonly = true
+			} else if bind[2] == "copy" {
+				copy_ = true
+			}
 		}
 		mntPnt := warewulfconf.MountEntry{
 			Source:   bind[0],
 			Dest:     dest,
 			ReadOnly: readonly,
+			Copy:     copy_,
 		}
 		mounts = append(mounts, &mntPnt)
 	}

userdocs/contents/containers.rst

@@ -213,6 +213,20 @@ 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``:
+
+.. code-block:: yaml
+   container mounts:
+   - source: /etc/resolv.conf
+     dest: /etc/resolv.conf
+     readonly: true
+
+.. note::
+   Instead of ``readonly: true`` you can set ``copy: true``. This causes the
+   source file to be copied to the container and removed if it was not
+   modified. This can be useful for files used for registrations.
+
 When the command completes, if anything within the container changed,
 the container will be rebuilt into a bootable static object
 automatically.