feat: Add clonefile implementation for linux (#1174)

Also cleanup the implementation a bit and expose the helper, it can be
useful for other tools we build

Author: dzbarsky

tools/common/BUILD.bazel

@@ -4,19 +4,26 @@ go_library(
     name = "common",
     srcs = [
         "clonefile_darwin.go",
+        "clonefile_linux.go",
         "clonefile_stub.go",
         "copy.go",
         "file.go",
     ],
     importpath = "github.com/bazel-contrib/bazel-lib/tools/common",
     visibility = ["//visibility:public"],
     deps = select({
+        "@io_bazel_rules_go//go/platform:android": [
+            "@org_golang_x_sys//unix",
+        ],
         "@io_bazel_rules_go//go/platform:darwin": [
             "@org_golang_x_sys//unix",
         ],
         "@io_bazel_rules_go//go/platform:ios": [
             "@org_golang_x_sys//unix",
         ],
+        "@io_bazel_rules_go//go/platform:linux": [
+            "@org_golang_x_sys//unix",
+        ],
         "//conditions:default": [],
     }),
 )

tools/common/clonefile_darwin.go

@@ -9,15 +9,14 @@ import (
 )
 
 // https://keith.github.io/xcode-man-pages/clonefile.2.html
-func cloneFile(src, dst string) (supported bool, err error) {
-	supported = true
-	if err = unix.Clonefile(src, dst, 0); err != nil {
-		err = &os.LinkError{
+func CloneFile(src, dst string) error {
+	if err := unix.Clonefile(src, dst, 0); err != nil {
+		return &os.LinkError{
 			Op:  "clonefile",
 			Old: src,
 			New: dst,
 			Err: err,
 		}
 	}
-	return
+	return nil
 }

tools/common/clonefile_linux.go

@@ -0,0 +1,40 @@
+//go:build linux
+
+package common
+
+import (
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+// FICLONE clones the contents of srcFd into the file referred to by dstFd.
+// #define FICLONE _IOW(0x94, 9, int)  /* 0x40049409 */
+const _FICLONE = 0x40049409
+
+func CloneFile(src, dst string) error {
+	source, err := os.Open(src)
+	if err != nil {
+		return err
+	}
+	defer source.Close()
+
+	destination, err := os.Create(dst)
+	if err != nil {
+		return err
+	}
+	defer destination.Close()
+
+	// Perform ioctl on the destination FD, passing the source FD as the arg.
+	// int ioctl(int dst_fd, FICLONE, int src_fd);
+	if err := unix.IoctlSetInt(int(destination.Fd()), _FICLONE, int(source.Fd())); err != nil {
+		return &os.LinkError{
+			Op:  "clonefile",
+			Old: src,
+			New: dst,
+			Err: err,
+		}
+	}
+
+	return nil
+}

tools/common/clonefile_stub.go

@@ -1,9 +1,7 @@
-//go:build !darwin
+//go:build !(darwin || linux)
 
 package common
 
-func cloneFile(src, dst string) (supported bool, err error) {
-	supported = false
-	err = nil
-	return
+func CloneFile(src, dst string) error {
+	return CopyFile(src, dst)
 }

tools/common/copy.go

@@ -56,27 +56,19 @@ func Copy(opts CopyOpts) {
 	if opts.verbose {
 		fmt.Printf("clonefile%s %v => %v\n", opModifier, opts.src, opts.dst)
 	}
-	switch supported, err := cloneFile(opts.src, opts.dst); {
-	case !supported:
-		if opts.verbose {
-			fmt.Print("clonefile skipped: not supported by platform\n")
-		}
-		// fallback to copy
-	case supported && err == nil:
+	err := CloneFile(opts.src, opts.dst)
+	if err == nil {
 		return
-	case supported && err != nil:
-		if opts.verbose {
-			fmt.Printf("clonefile failed: %v\n", err)
-			opModifier = fallback
-		}
-		// fallback to copy
 	}
 
-	// copy this file
 	if opts.verbose {
+		fmt.Printf("clonefile failed: %v\n", err)
 		fmt.Printf("copy%s %v => %v\n", opModifier, opts.src, opts.dst)
+		opModifier = fallback
 	}
-	err := CopyFile(opts.src, opts.dst)
+
+	// copy this file
+	err = CopyFile(opts.src, opts.dst)
 	if err != nil {
 		log.Fatal(err)
 	}