unix: add UV_FS_COPYFILE_FICLONE support

UV_FS_COPYFILE_FICLONE attemps to use copy-on-write
semantics in uv_fs_copyfile(). If CoW is not available,
it falls back to a normal copy operation.

Refs: https://github.com/libuv/libuv/pull/1465
PR-URL: https://github.com/libuv/libuv/pull/1491
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Santiago Gimeno <santiago.gimeno@gmail.com>

docs/src/fs.rst

@@ -249,6 +249,9 @@ API
     - `UV_FS_COPYFILE_EXCL`: If present, `uv_fs_copyfile()` will fail with
       `UV_EEXIST` if the destination path already exists. The default behavior
       is to overwrite the destination if it exists.
+    - `UV_FS_COPYFILE_FICLONE`: If present, `uv_fs_copyfile()` will attempt to
+      create a copy-on-write reflink. If the underlying platform does not
+      support copy-on-write, then a fallback copy mechanism is used.
 
     .. warning::
         If the destination path is created, but an error occurs while copying
@@ -258,6 +261,8 @@ API
 
     .. versionadded:: 1.14.0
 
+    .. versionchanged:: 1.20.0 `UV_FS_COPYFILE_FICLONE` is supported.
+
 .. c:function:: int uv_fs_sendfile(uv_loop_t* loop, uv_fs_t* req, uv_file out_fd, uv_file in_fd, int64_t in_offset, size_t length, uv_fs_cb cb)
 
     Limited equivalent to :man:`sendfile(2)`.

include/uv.h

@@ -1190,6 +1190,12 @@ UV_EXTERN int uv_fs_write(uv_loop_t* loop,
  */
 #define UV_FS_COPYFILE_EXCL   0x0001
 
+/*
+ * This flag can be used with uv_fs_copyfile() to attempt to create a reflink.
+ * If copy-on-write is not supported, a fallback copy mechanism is used.
+ */
+#define UV_FS_COPYFILE_FICLONE 0x0002
+
 UV_EXTERN int uv_fs_copyfile(uv_loop_t* loop,
                              uv_fs_t* req,
                              const char* path,

src/unix/fs.c

@@ -62,6 +62,9 @@
 
 #if defined(__APPLE__)
 # include <copyfile.h>
+#elif defined(__linux__) && !defined(FICLONE)
+# include <sys/ioctl.h>
+# define FICLONE _IOW(0x94, 9, int)
 #endif
 
 #define INIT(subtype)                                                         \
@@ -790,6 +793,10 @@ static ssize_t uv__fs_copyfile(uv_fs_t* req) {
   if (req->flags & UV_FS_COPYFILE_EXCL)
     flags |= COPYFILE_EXCL;
 
+#ifdef COPYFILE_CLONE
+  if (req->flags & UV_FS_COPYFILE_FICLONE)
+    flags |= COPYFILE_CLONE;
+#endif
   return copyfile(req->path, req->new_path, NULL, flags);
 #else
   uv_fs_t fs_req;
@@ -842,6 +849,21 @@ static ssize_t uv__fs_copyfile(uv_fs_t* req) {
     goto out;
   }
 
+#ifdef FICLONE
+  if (req->flags & UV_FS_COPYFILE_FICLONE) {
+    if (ioctl(dstfd, FICLONE, srcfd) == -1) {
+      /* If an error occurred that the sendfile fallback also won't handle,
+         then exit. Otherwise, fall through to try using sendfile(). */
+      if (errno != ENOTTY && errno != EOPNOTSUPP && errno != EXDEV) {
+        err = -errno;
+        goto out;
+      }
+    } else {
+      goto out;
+    }
+  }
+#endif
+
   bytes_to_send = statsbuf.st_size;
   in_offset = 0;
   while (bytes_to_send != 0) {
@@ -1504,7 +1526,7 @@ int uv_fs_copyfile(uv_loop_t* loop,
                    uv_fs_cb cb) {
   INIT(COPYFILE);
 
-  if (flags & ~UV_FS_COPYFILE_EXCL)
+  if (flags & ~(UV_FS_COPYFILE_EXCL | UV_FS_COPYFILE_FICLONE))
     return UV_EINVAL;
 
   PATH2;

src/win/fs.c

@@ -2334,7 +2334,7 @@ int uv_fs_copyfile(uv_loop_t* loop,
 
   INIT(UV_FS_COPYFILE);
 
-  if (flags & ~UV_FS_COPYFILE_EXCL)
+  if (flags & ~(UV_FS_COPYFILE_EXCL | UV_FS_COPYFILE_FICLONE))
     return UV_EINVAL;
 
   err = fs__capture_path(req, path, new_path, cb != NULL);

test/test-fs-copyfile.c

@@ -168,6 +168,13 @@ TEST_IMPL(fs_copyfile) {
   r = uv_fs_copyfile(loop, &req, fixture, dst, -1, fail_cb);
   ASSERT(r == UV_EINVAL);
   uv_run(loop, UV_RUN_DEFAULT);
+
+  /* Copies file using UV_FS_COPYFILE_FICLONE. */
+  unlink(dst);
+  r = uv_fs_copyfile(NULL, &req, fixture, dst, UV_FS_COPYFILE_FICLONE, NULL);
+  ASSERT(r == 0);
+  handle_result(&req);
+
   unlink(dst); /* Cleanup */
   return 0;
 }