Use copy_file_range to copy files

The copy_file_range syscall (introduced in Linux kernel
version 4.5) can copy files more efficiently via server-side
copy etc.
* admin/merge-gnulib (GNULIB_MODULES): Add copy-file-range.
* lib/copy-file-range.c, m4/copy-file-range.m4:
New files, copied from Gnulib.
* lib/gnulib.mk.in, m4/gnulib-comp.m4: Regenerate.
* src/fileio.c (Fcopy_file): Try copy_file_range first,
falling back on read+write only if copy_file_range failed or
if the input is empty and so could be a /proc file.

1 files changed, 33 insertions, 0 deletions

diff --git a/lib/copy-file-range.c b/lib/copy-file-range.c
new file mode 100644
index 00000000000..39b5efbc1cc
--- /dev/null
+++ b/lib/copy-file-range.c
@@ -0,0 +1,33 @@
+/* Stub for copy_file_range
+   Copyright 2019 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <https://www.gnu.org/licenses/>.  */
+
+#include <config.h>
+
+#include <unistd.h>
+
+#include <errno.h>
+
+ssize_t
+copy_file_range (int infd, off_t *pinoff,
+                 int outfd, off_t *poutoff,
+                 size_t length, unsigned int flags)
+{
+  /* There is little need to emulate copy_file_range with read+write,
+     since programs that use copy_file_range must fall back on
+     read+write anyway.  */
+  errno = ENOSYS;
+  return -1;
+}