Add --preservefds to podman run

Add --preservefds to podman run. close #6458

Signed-off-by: Qi Wang <[email protected]>

cmd/podman/common/create_opts.go

@@ -69,6 +69,7 @@ type ContainerCLIOpts struct {
 	PIDsLimit         int64
 	Pod               string
 	PodIDFile         string
+	PreserveFDs       uint
 	Privileged        bool
 	PublishAll        bool
 	Pull              string

cmd/podman/common/specgen.go

@@ -609,6 +609,7 @@ func FillOutSpecGen(s *specgen.SpecGenerator, c *ContainerCLIOpts, args []string
 	}
 	s.LogConfiguration.Options = logOpts
 	s.Name = c.Name
+	s.PreserveFDs = c.PreserveFDs
 
 	s.OOMScoreAdj = &c.OOMScoreAdj
 	if c.Restart != "" {

cmd/podman/containers/run.go

@@ -61,10 +61,12 @@ func runFlags(flags *pflag.FlagSet) {
 	flags.SetNormalizeFunc(common.AliasFlags)
 	flags.BoolVar(&runOpts.SigProxy, "sig-proxy", true, "Proxy received signals to the process")
 	flags.BoolVar(&runRmi, "rmi", false, "Remove container image unless used by other containers")
+	flags.UintVar(&runOpts.PreserveFDs, "preserve-fds", 0, "Pass a number of additional file descriptors into the container")
 	if registry.IsRemote() {
 		_ = flags.MarkHidden("authfile")
 		_ = flags.MarkHidden("env-host")
 		_ = flags.MarkHidden("http-proxy")
+		_ = flags.MarkHidden("preserve-fds")
 	}
 	// Not sure we want these exposed yet.  If we do, they need to be documented in man pages
 	_ = flags.MarkHidden("override-arch")
@@ -163,6 +165,7 @@ func run(cmd *cobra.Command, args []string) error {
 	}
 	runOpts.Detach = cliVals.Detach
 	runOpts.DetachKeys = cliVals.DetachKeys
+	cliVals.PreserveFDs = runOpts.PreserveFDs
 	s := specgen.NewSpecGenerator(args[0], cliVals.RootFS)
 	if err := common.FillOutSpecGen(s, &cliVals, args); err != nil {
 		return err

completions/bash/podman

@@ -2103,6 +2103,7 @@ _podman_container_run() {
 		--pids-limit
 		--pod
 		--pod-id-file
+		--preserve-fds
 		--publish -p
 		--pull
 		--runtime

docs/source/markdown/podman-run.1.md

@@ -609,6 +609,10 @@ If a container is run with a pod, and the pod has an infra-container, the infra-
 
 Run container in an existing pod and read the pod's ID from the specified file.  If a container is run within a pod, and the pod has an infra-container, the infra-container will be started before the container is.
 
+**--preserve-fds**=*N*
+
+Pass down to the process N additional file descriptors (in addition to 0, 1, 2).  The total FDs will be 3+N.
+
 **--privileged**=**true**|**false**
 
 Give extended privileges to this container. The default is **false**.

libpod/container.go

@@ -418,6 +418,11 @@ type ContainerConfig struct {
 
 	// HealthCheckConfig has the health check command and related timings
 	HealthCheckConfig *manifest.Schema2HealthConfig `json:"healthcheck"`
+
+	// PreserveFDs is a number of additional file descriptors (in addition
+	// to 0, 1, 2) that will be passed to the executed process. The total FDs
+	// passed will be 3 + PreserveFDs.
+	PreserveFDs uint `json:"preserveFds,omitempty"`
 }
 
 // ContainerNamedVolume is a named volume that will be mounted into the

libpod/oci_conmon_linux.go

@@ -904,6 +904,10 @@ func (r *ConmonOCIRuntime) createOCIContainer(ctr *Container, restoreOptions *Co
 		}
 	}
 
+	if ctr.config.PreserveFDs > 0 {
+		args = append(args, formatRuntimeOpts("--preserve-fds", fmt.Sprintf("%d", ctr.config.PreserveFDs))...)
+	}
+
 	if restoreOptions != nil {
 		args = append(args, "--restore", ctr.CheckpointPath())
 		if restoreOptions.TCPEstablished {
@@ -935,8 +939,16 @@ func (r *ConmonOCIRuntime) createOCIContainer(ctr *Container, restoreOptions *Co
 		return err
 	}
 
+	if ctr.config.PreserveFDs > 0 {
+		for fd := 3; fd < int(3+ctr.config.PreserveFDs); fd++ {
+			cmd.ExtraFiles = append(cmd.ExtraFiles, os.NewFile(uintptr(fd), fmt.Sprintf("fd-%d", fd)))
+		}
+	}
+
 	cmd.Env = r.conmonEnv
-	cmd.Env = append(cmd.Env, fmt.Sprintf("_OCI_SYNCPIPE=%d", 3), fmt.Sprintf("_OCI_STARTPIPE=%d", 4))
+	// we don't want to step on users fds they asked to preserve
+	// Since 0-2 are used for stdio, start the fds we pass in at preserveFDs+3
+	cmd.Env = append(cmd.Env, fmt.Sprintf("_OCI_SYNCPIPE=%d", ctr.config.PreserveFDs+3), fmt.Sprintf("_OCI_STARTPIPE=%d", ctr.config.PreserveFDs+4))
 	cmd.Env = append(cmd.Env, conmonEnv...)
 	cmd.ExtraFiles = append(cmd.ExtraFiles, childSyncPipe, childStartPipe)
 	cmd.ExtraFiles = append(cmd.ExtraFiles, envFiles...)
@@ -1018,6 +1030,16 @@ func (r *ConmonOCIRuntime) createOCIContainer(ctr *Container, restoreOptions *Co
 		ctr.state.ConmonPID = conmonPID
 	}
 
+	if ctr.config.PreserveFDs > 0 {
+		for fd := 3; fd < int(3+ctr.config.PreserveFDs); fd++ {
+			// These fds were passed down to the runtime.  Close them
+			// and not interfere
+			if err := os.NewFile(uintptr(fd), fmt.Sprintf("fd-%d", fd)).Close(); err != nil {
+				logrus.Debugf("unable to close file fd-%d", fd)
+			}
+		}
+	}
+
 	return nil
 }
 

libpod/options.go

@@ -1369,6 +1369,18 @@ func WithHealthCheck(healthCheck *manifest.Schema2HealthConfig) CtrCreateOption
 	}
 }
 
+// WithPreserveFDs forwards from the process running Libpod into the container
+// the given number of extra FDs (starting after the standard streams) to the created container
+func WithPreserveFDs(fd uint) CtrCreateOption {
+	return func(ctr *Container) error {
+		if ctr.valid {
+			return define.ErrCtrFinalized
+		}
+		ctr.config.PreserveFDs = fd
+		return nil
+	}
+}
+
 // WithCreateCommand adds the full command plus arguments of the current
 // process to the container config.
 func WithCreateCommand() CtrCreateOption {

pkg/domain/entities/containers.go

@@ -294,6 +294,7 @@ type ContainerRunOptions struct {
 	ErrorStream  *os.File
 	InputStream  *os.File
 	OutputStream *os.File
+	PreserveFDs  uint
 	Rm           bool
 	SigProxy     bool
 	Spec         *specgen.SpecGenerator

pkg/specgen/generate/container_create.go

@@ -104,6 +104,10 @@ func MakeContainer(ctx context.Context, rt *libpod.Runtime, s *specgen.SpecGener
 		return nil, err
 	}
 
+	if s.PreserveFDs > 0 {
+		options = append(options, libpod.WithPreserveFDs(s.PreserveFDs))
+	}
+
 	opts, err := createContainerOptions(ctx, rt, s, pod, finalVolumes, newImage)
 	if err != nil {
 		return nil, err

pkg/specgen/specgen.go

@@ -130,6 +130,11 @@ type ContainerBasicConfig struct {
 	// Remove indicates if the container should be removed once it has been started
 	// and exits
 	Remove bool `json:"remove"`
+	// PreserveFDs is a number of additional file descriptors (in addition
+	// to 0, 1, 2) that will be passed to the executed process. The total FDs
+	// passed will be 3 + PreserveFDs.
+	// set tags as `json:"-"` for not supported remote
+	PreserveFDs uint `json:"-"`
 }
 
 // ContainerStorageConfig contains information on the storage configuration of a

test/e2e/run_test.go

@@ -1015,4 +1015,16 @@ USER mail`
 			Expect(session.ExitCode()).To(Equal(0))
 		}
 	})
+
+	It("podman run --preserve-fds", func() {
+		devNull, err := os.Open("/dev/null")
+		Expect(err).To(BeNil())
+		defer devNull.Close()
+		files := []*os.File{
+			devNull,
+		}
+		session := podmanTest.PodmanExtraFiles([]string{"run", "--preserve-fds", "1", ALPINE, "ls"}, files)
+		session.WaitWithDefaultTimeout()
+		Expect(session.ExitCode()).To(Equal(0))
+	})
 })

test/system/030-run.bats

@@ -61,6 +61,18 @@ echo $rand        |   0 | $rand
     is "$tests_run" "$(grep . <<<$tests | wc -l)" "Ran the full set of tests"
 }
 
+# 'run --preserve-fds' passes a number of additional file descriptors into the container
+@test "podman run --preserve-fds" {
+    skip "enable this once #6653 is fixed"
+    skip_if_remote
+
+    content=$(random_string 20)
+    echo "$content" > $PODMAN_TMPDIR/tempfile
+
+    run_podman run --rm -i --preserve-fds=2 $IMAGE sh -c "cat <&4" 4<$PODMAN_TMPDIR/tempfile
+    is "$output" "$content" "container read input from fd 4"
+}
+
 @test "podman run - uidmapping has no /sys/kernel mounts" {
     skip_if_rootless "cannot umount as rootless"
     skip_if_remote "TODO Fix this for remote case"