Handle hard links in remote builds

Fixes: https://github.com/containers/podman/issues/9893

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

Makefile

@@ -382,6 +382,9 @@ bin/podman.cross.%: .gopathok
 .PHONY: local-cross
 local-cross: $(CROSS_BUILD_TARGETS) ## Cross compile podman binary for multiple architectures
 
+.PHONY: cross
+cross: local-cross
+
 # Update nix/nixpkgs.json its latest stable commit
 .PHONY: nixpkgs
 nixpkgs:

pkg/bindings/images/build.go

@@ -28,6 +28,11 @@ import (
 	"github.com/sirupsen/logrus"
 )
 
+type devino struct {
+	Dev uint64
+	Ino uint64
+}
+
 var (
 	iidRegex = regexp.MustCompile(`^[0-9a-f]{12}`)
 )
@@ -402,7 +407,7 @@ func nTar(excludes []string, sources ...string) (io.ReadCloser, error) {
 		defer pw.Close()
 		defer gw.Close()
 		defer tw.Close()
-
+		seen := make(map[devino]string)
 		for _, src := range sources {
 			s, err := filepath.Abs(src)
 			if err != nil {
@@ -431,25 +436,40 @@ func nTar(excludes []string, sources ...string) (io.ReadCloser, error) {
 				}
 
 				if info.Mode().IsRegular() { // add file item
-					f, lerr := os.Open(path)
-					if lerr != nil {
-						return lerr
+					di, isHardLink := checkHardLink(info)
+					if err != nil {
+						return err
 					}
 
-					hdr, lerr := tar.FileInfoHeader(info, name)
-					if lerr != nil {
-						f.Close()
-						return lerr
+					hdr, err := tar.FileInfoHeader(info, "")
+					if err != nil {
+						return err
 					}
+					orig, ok := seen[di]
+					if ok {
+						hdr.Typeflag = tar.TypeLink
+						hdr.Linkname = orig
+						hdr.Size = 0
+
+						return tw.WriteHeader(hdr)
+					}
+					f, err := os.Open(path)
+					if err != nil {
+						return err
+					}
+
 					hdr.Name = name
-					if lerr := tw.WriteHeader(hdr); lerr != nil {
+					if err := tw.WriteHeader(hdr); err != nil {
 						f.Close()
-						return lerr
+						return err
 					}
 
-					_, cerr := io.Copy(tw, f)
+					_, err = io.Copy(tw, f)
 					f.Close()
-					return cerr
+					if err == nil && isHardLink {
+						seen[di] = name
+					}
+					return err
 				} else if info.Mode().IsDir() { // add folders
 					hdr, lerr := tar.FileInfoHeader(info, name)
 					if lerr != nil {

pkg/bindings/images/build_unix.go

@@ -0,0 +1,16 @@
+// +build !windows
+
+package images
+
+import (
+	"os"
+	"syscall"
+)
+
+func checkHardLink(fi os.FileInfo) (devino, bool) {
+	st := fi.Sys().(*syscall.Stat_t)
+	return devino{
+		Dev: uint64(st.Dev),
+		Ino: uint64(st.Ino),
+	}, st.Nlink > 1
+}

pkg/bindings/images/build_windows.go

@@ -0,0 +1,9 @@
+package images
+
+import (
+	"os"
+)
+
+func checkHardLink(fi os.FileInfo) (devino, bool) {
+	return devino{}, false
+}

test/system/070-build.bats

@@ -766,6 +766,26 @@ EOF
     is "$output" ".*/tmp/bogus: no such file or directory"
 }
 
+@test "podman build COPY hardlinks " {
+    tmpdir=$PODMAN_TMPDIR/build-test
+    mkdir -p $tmpdir
+
+    dockerfile=$tmpdir/Dockerfile
+    cat >$dockerfile <<EOF
+FROM $IMAGE
+COPY . /test
+EOF
+    ln $dockerfile $tmpdir/hardlink
+
+    run_podman build -t build_test $tmpdir
+    run_podman run --rm build_test stat -c '%i' /test/Dockerfile
+    dinode=$output
+    run_podman run --rm build_test stat -c '%i' /test/hardlink
+    is "$output"   "$dinode"   "COPY hardlinks work"
+
+    run_podman rmi -f build_test
+}
+
 function teardown() {
     # A timeout or other error in 'build' can leave behind stale images
     # that podman can't even see and which will cascade into subsequent