libpod: Move jointMountAndExec to container_copy_linux.go

This also moves the logic for resolving paths in running and stopped
containers tp container_copy_linux.go.

On FreeBSD, we can execute the function argument to joinMountAndExec
directly using host-relative paths since the host mount namespace
includes all the container mounts.

[NO NEW TESTS NEEDED]

Signed-off-by: Doug Rabson <dfr@rabson.org>

1 files changed, 88 insertions, 0 deletions

diff --git a/libpod/container_copy_linux.go b/libpod/container_copy_linux.go
new file mode 100644
index 000000000..3b029f08f
--- /dev/null
+++ b/libpod/container_copy_linux.go
@@ -0,0 +1,88 @@
+package libpod
+
+import (
+	"fmt"
+	"os"
+	"runtime"
+
+	"github.com/containers/podman/v4/libpod/define"
+	"golang.org/x/sys/unix"
+)
+
+// joinMountAndExec executes the specified function `f` inside the container's
+// mount and PID namespace.  That allows for having the exact view on the
+// container's file system.
+//
+// Note, if the container is not running `f()` will be executed as is.
+func (c *Container) joinMountAndExec(f func() error) error {
+	if c.state.State != define.ContainerStateRunning {
+		return f()
+	}
+
+	// Container's running, so we need to execute `f()` inside its mount NS.
+	errChan := make(chan error)
+	go func() {
+		runtime.LockOSThread()
+
+		// Join the mount and PID NS of the container.
+		getFD := func(ns LinuxNS) (*os.File, error) {
+			nsPath, err := c.namespacePath(ns)
+			if err != nil {
+				return nil, err
+			}
+			return os.Open(nsPath)
+		}
+
+		mountFD, err := getFD(MountNS)
+		if err != nil {
+			errChan <- err
+			return
+		}
+		defer mountFD.Close()
+
+		inHostPidNS, err := c.inHostPidNS()
+		if err != nil {
+			errChan <- fmt.Errorf("checking inHostPidNS: %w", err)
+			return
+		}
+		var pidFD *os.File
+		if !inHostPidNS {
+			pidFD, err = getFD(PIDNS)
+			if err != nil {
+				errChan <- err
+				return
+			}
+			defer pidFD.Close()
+		}
+
+		if err := unix.Unshare(unix.CLONE_NEWNS); err != nil {
+			errChan <- err
+			return
+		}
+
+		if pidFD != nil {
+			if err := unix.Setns(int(pidFD.Fd()), unix.CLONE_NEWPID); err != nil {
+				errChan <- err
+				return
+			}
+		}
+		if err := unix.Setns(int(mountFD.Fd()), unix.CLONE_NEWNS); err != nil {
+			errChan <- err
+			return
+		}
+
+		// Last but not least, execute the workload.
+		errChan <- f()
+	}()
+	return <-errChan
+}
+
+func (c *Container) resolveCopyTarget(mountPoint string, containerPath string) (string, string, error) {
+	// If the container is running, we will execute the copy
+	// inside the container's mount namespace so we return a path
+	// relative to the container's root.
+	if c.state.State == define.ContainerStateRunning {
+		return "/", c.pathAbs(containerPath), nil
+	}
+	return c.resolvePath(mountPoint, containerPath)
+}