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.

2 files changed, 44 insertions, 0 deletions

diff --git a/m4/copy-file-range.m4 b/m4/copy-file-range.m4
new file mode 100644
index 00000000000..20fd05697fe
--- /dev/null
+++ b/m4/copy-file-range.m4
@@ -0,0 +1,36 @@
+# copy-file-range.m4
+dnl Copyright 2019 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN([gl_FUNC_COPY_FILE_RANGE],
+[
+  AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
+
+  dnl Persuade glibc <unistd.h> to declare copy_file_range.
+  AC_REQUIRE([AC_USE_SYSTEM_EXTENSIONS])
+
+  dnl Use AC_LINK_IFELSE, rather than AC_CHECK_FUNCS or a variant,
+  dnl since we don't want AC_CHECK_FUNCS's checks for glibc stubs.
+  dnl Programs that use copy_file_range must fall back on read+write
+  dnl anyway, and there's little point to substituting the Gnulib stub
+  dnl for a glibc stub.
+  AC_CACHE_CHECK([for copy_file_range], [gl_cv_func_copy_file_range],
+    [AC_LINK_IFELSE(
+       [AC_LANG_PROGRAM(
+          [[#include <unistd.h>
+          ]],
+          [[ssize_t (*func) (int, off_t *, int, off_t, size_t, unsigned)
+              = copy_file_range;
+            return func (0, 0, 0, 0, 0, 0) & 127;
+          ]])
+       ],
+       [gl_cv_func_copy_file_range=yes],
+       [gl_cv_func_copy_file_range=no])
+    ])
+
+  if test "$gl_cv_func_copy_file_range" != yes; then
+    HAVE_COPY_FILE_RANGE=0
+  fi
+])
diff --git a/m4/gnulib-comp.m4 b/m4/gnulib-comp.m4
index 0a7a30e5ae2..4627575bf63 100644
--- a/m4/gnulib-comp.m4
+++ b/m4/gnulib-comp.m4
@@ -56,6 +56,7 @@ AC_DEFUN([gl_EARLY],
   # Code from module clock-time:
   # Code from module cloexec:
   # Code from module close-stream:
+  # Code from module copy-file-range:
   # Code from module count-leading-zeros:
   # Code from module count-one-bits:
   # Code from module count-trailing-zeros:
@@ -201,6 +202,11 @@ AC_DEFUN([gl_INIT],
   AC_CHECK_FUNCS_ONCE([readlinkat])
   gl_CLOCK_TIME
   gl_MODULE_INDICATOR([close-stream])
+  gl_FUNC_COPY_FILE_RANGE
+  if test $HAVE_COPY_FILE_RANGE = 0; then
+    AC_LIBOBJ([copy-file-range])
+  fi
+  gl_UNISTD_MODULE_INDICATOR([copy-file-range])
   gl_COUNT_LEADING_ZEROS
   gl_COUNT_ONE_BITS
   gl_COUNT_TRAILING_ZEROS
@@ -846,6 +852,7 @@ AC_DEFUN([gl_FILE_LIST], [
   lib/cloexec.h
   lib/close-stream.c
   lib/close-stream.h
+  lib/copy-file-range.c
   lib/count-leading-zeros.c
   lib/count-leading-zeros.h
   lib/count-one-bits.c
@@ -995,6 +1002,7 @@ AC_DEFUN([gl_FILE_LIST], [
   m4/builtin-expect.m4
   m4/byteswap.m4
   m4/clock_time.m4
+  m4/copy-file-range.m4
   m4/count-leading-zeros.m4
   m4/count-one-bits.m4
   m4/count-trailing-zeros.m4