podman cp: support copying on tmpfs mounts

Traditionally, the path resolution for containers has been resolved on
the *host*; relative to the container's mount point or relative to
specified bind mounts or volumes.

While this works nicely for non-running containers, it poses a problem
for running ones.  In that case, certain kinds of mounts (e.g., tmpfs)
will not resolve correctly.  A tmpfs is held in memory and hence cannot
be resolved relatively to the container's mount point.  A copy operation
will succeed but the data will not show up inside the container.

To support these kinds of mounts, we need to join the *running*
container's mount namespace (and PID namespace) when copying.

Note that this change implies moving the copy and stat logic into
`libpod` since we need to keep the container locked to avoid race
conditions.  The immediate benefit is that all logic is now inside
`libpod`; the code isn't scattered anymore.

Further note that Docker does not support copying to tmpfs mounts.

Tests have been extended to cover *both* path resolutions for running
and created containers.  New tests have been added to exercise the
tmpfs-mount case.

For the record: Some tests could be improved by using `start -a` instead
of a start-exec sequence.  Unfortunately, `start -a` is flaky in the CI
which forced me to use the more expensive start-exec option.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

1 files changed, 2 insertions, 9 deletions

diff --git a/pkg/copy/fileinfo.go b/pkg/copy/fileinfo.go
index b95bcd90c..fb711311c 100644
--- a/pkg/copy/fileinfo.go
+++ b/pkg/copy/fileinfo.go
@@ -7,8 +7,8 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
-	"time"
 
+	"github.com/containers/podman/v3/libpod/define"
 	"github.com/pkg/errors"
 )
 
@@ -22,14 +22,7 @@ var ErrENOENT = errors.New("No such file or directory")
 
 // FileInfo describes a file or directory and is returned by
 // (*CopyItem).Stat().
-type FileInfo struct {
-	Name       string      `json:"name"`
-	Size       int64       `json:"size"`
-	Mode       os.FileMode `json:"mode"`
-	ModTime    time.Time   `json:"mtime"`
-	IsDir      bool        `json:"isDir"`
-	LinkTarget string      `json:"linkTarget"`
-}
+type FileInfo = define.FileInfo
 
 // EncodeFileInfo serializes the specified FileInfo as a base64 encoded JSON
 // payload.  Intended for Docker compat.