[Emacs-diffs] master 9b21d9f 1/3: copy-file now uses GNU/Linux file cloning

[Paul Eggert]

branch: master
commit 9b21d9f9110445846dce25c3505c4ee04572fade
Author: Paul Eggert <address@hidden>
Commit: Paul Eggert <address@hidden>

    copy-file now uses GNU/Linux file cloning
    
    From a suggestion by Kieran Colford (see Bug#23904).
    * configure.ac: Check for linux/fs.h.
    * src/fileio.c [HAVE_LINUX_FS_H]: Include sys/ioctl.h and linux/fs.h.
    (clone_file): New function.
    (Fcopy_file): Use it.
---
 configure.ac |    1 +
 src/fileio.c |   33 +++++++++++++++++++++++++--------
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/configure.ac b/configure.ac
index 9856228..82a672b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1638,6 +1638,7 @@ fi
 
 dnl checks for header files
 AC_CHECK_HEADERS_ONCE(
+  linux/fs.h
   malloc.h
   sys/systeminfo.h
   sys/sysinfo.h
diff --git a/src/fileio.c b/src/fileio.c
index bf6bf62..b4316b3 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -52,6 +52,11 @@ along with GNU Emacs.  If not, see 
<http://www.gnu.org/licenses/>.  */
 #include "region-cache.h"
 #include "frame.h"
 
+#ifdef HAVE_LINUX_FS_H
+# include <sys/ioctl.h>
+# include <linux/fs.h>
+#endif
+
 #ifdef WINDOWSNT
 #define NOMINMAX 1
 #include <windows.h>
@@ -1829,6 +1834,16 @@ barf_or_query_if_file_exists (Lisp_Object absname, bool 
known_to_exist,
     }
 }
 
+/* Copy data to DEST from SOURCE if possible.  Return true if OK.  */
+static bool
+clone_file (int dest, int source)
+{
+#ifdef FICLONE
+  return ioctl (dest, FICLONE, source) == 0;
+#endif
+  return false;
+}
+
 DEFUN ("copy-file", Fcopy_file, Scopy_file, 2, 6,
        "fCopy file: \nGCopy %s to file: \np\nP",
        doc: /* Copy FILE to NEWNAME.  Both args must be strings.
@@ -1975,7 +1990,7 @@ permissions.  */)
 
   record_unwind_protect_int (close_file_unwind, ofd);
 
-  off_t oldsize = 0, newsize = 0;
+  off_t oldsize = 0, newsize;
 
   if (already_exists)
     {
@@ -1991,17 +2006,19 @@ permissions.  */)
 
   immediate_quit = 1;
   QUIT;
-  while (true)
+
+  if (clone_file (ofd, ifd))
+    newsize = st.st_size;
+  else
     {
       char buf[MAX_ALLOCA];
-      ptrdiff_t n = emacs_read (ifd, buf, sizeof buf);
+      ptrdiff_t n;
+      for (newsize = 0; 0 < (n = emacs_read (ifd, buf, sizeof buf));
+          newsize += n)
+       if (emacs_write_sig (ofd, buf, n) != n)
+         report_file_error ("Write error", newname);
       if (n < 0)
        report_file_error ("Read error", file);
-      if (n == 0)
-       break;
-      if (emacs_write_sig (ofd, buf, n) != n)
-       report_file_error ("Write error", newname);
-      newsize += n;
     }
 
   /* Truncate any existing output file after writing the data.  This