Re: BTRFS file clone support for cp

[Jim Meyering]

Giuseppe Scrivano wrote:
> Jim Meyering <address@hidden> writes:
>
>>>> Adding this optimization should not change the meaning of
>>>> --sparse=always.
>>>
>>> So do you want to use it only when --sparse=auto is used?
>>
>> Precisely.
>
> I cleaned the patch a bit, the clone operation is done only when
> --sparse=auto is used.

Thanks.
Here's an adjusted version that moves the in-function #ifdefs into
a helper function and includes sys/ioctl.h whenever HAVE_SYS_IOCTL_H
is defined.  I'll adjust indentation in a separate patch.

>From 2be19afe6a06bdf4172ab10ff657a32121960217 Mon Sep 17 00:00:00 2001
From: Giuseppe Scrivano <address@hidden>
Date: Sat, 25 Jul 2009 16:35:27 +0200
Subject: [PATCH] cp: support btrfs' copy-on-write file clone operation

* src/copy.c [HAVE_SYS_IOCTL_H]: Include <sys/ioctl.h>.
(clone_file): New function.
(copy_reg): Use the btrfs clone operation if possible.
---
 src/copy.c |   27 +++++++++++++++++++++++++++
 1 files changed, 27 insertions(+), 0 deletions(-)

diff --git a/src/copy.c b/src/copy.c
index 4c8c432..34af802 100644
--- a/src/copy.c
+++ b/src/copy.c
@@ -61,6 +61,10 @@
 # include "verror.h"
 #endif

+#if HAVE_SYS_IOCTL_H
+# include <sys/ioctl.h>
+#endif
+
 #ifndef HAVE_FCHOWN
 # define HAVE_FCHOWN false
 # define fchown(fd, uid, gid) (-1)
@@ -114,6 +118,20 @@ static bool owner_failure_ok (struct cp_options const *x);
 static char const *top_level_src_name;
 static char const *top_level_dst_name;

+/* Perform the O(1) btrfs clone operation, if possible.
+   Upon success, return 0.  Otherwise, return -1 and set errno.  */
+static inline int
+clone_file (int dest_fd, int src_fd)
+{
+#ifdef __linux__
+# define BTRFS_IOC_CLONE 1074041865
+  return ioctl (dest_fd, BTRFS_IOC_CLONE, src_fd);
+#else
+  errno = ENOTSUP;
+  return -1;
+#endif
+}
+
 /* FIXME: describe */
 /* FIXME: rewrite this to use a hash table so we avoid the quadratic
    performance hit that's probably noticeable only on trees deeper
@@ -444,6 +462,7 @@ copy_reg (char const *src_name, char const *dst_name,
   struct stat sb;
   struct stat src_open_sb;
   bool return_val = true;
+  bool copied = false;

   source_desc = open (src_name,
                      (O_RDONLY | O_BINARY
@@ -589,6 +608,14 @@ copy_reg (char const *src_name, char const *dst_name,
       goto close_src_and_dst_desc;
     }

+  /* If --sparse=auto is in effect, attempt a btrfs clone operation.
+     If the operation is not supported or it fails then copy the file
+     in the usual way.  */
+  if (x->sparse_mode == SPARSE_AUTO
+      && clone_file (dest_desc, source_desc) == 0)
+    copied = true;
+
+  if (!copied)
   {
     typedef uintptr_t word;
     off_t n_read_total = 0;
--
1.6.4.rc3.195.g2b05