Btrfs clone support in copy operations

Btrfs clone support in copy operations

[Kieran Colford]

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I've put together a patch for supporting the btrfs clone operation for
copying

diff --git a/src/fileio.c b/src/fileio.c
index b1f9d3c..d7c1e6e 100644
--- a/src/fileio.c
+++ b/src/fileio.c
@@ -21,6 +21,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include <limits.h>
 #include <fcntl.h>
 #include "sysstdio.h"
+#include <sys/ioctl.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <unistd.h>
@@ -1988,6 +1989,16 @@ permissions.  */)
 	oldsize = out_st.st_size;
     }
 
+  /* Perform the O(1) btrfs clone operation, if possible. */
+#ifdef __linux__
+# undef BTRFS_IOCTL_MAGIC
+# define BTRFS_IOCTL_MAGIC 0x94
+# undef BTRFS_IOC_CLONE
+# define BTRFS_IOC_CLONE _IOW (BTRFS_IOCTL_MAGIC, 9, int)
+  if (ioctl (ofd, BTRFS_IOC_CLONE, ifd) == 0)
+    goto done_copy;
+#endif
+
   immediate_quit = 1;
   QUIT;
   while (true)
@@ -2011,6 +2022,8 @@ permissions.  */)
 
   immediate_quit = 0;
 
+ done_copy:
+
 #ifndef MSDOS
   /* Preserve the original file permissions, and if requested, also its
      owner and group.  */

-- 
Kieran Colford <kieran@kcolford.com>

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Re: Btrfs clone support in copy operations

[sbaugh]

Kieran Colford <kieran@kcolford.com> writes:
> +  /* Perform the O(1) btrfs clone operation, if possible. */
> +#ifdef __linux__
> +# undef BTRFS_IOCTL_MAGIC
> +# define BTRFS_IOCTL_MAGIC 0x94
> +# undef BTRFS_IOC_CLONE
> +# define BTRFS_IOC_CLONE _IOW (BTRFS_IOCTL_MAGIC, 9, int)
> +  if (ioctl (ofd, BTRFS_IOC_CLONE, ifd) == 0)
> +    goto done_copy;
> +#endif

Perhaps you should use the FICLONE flag, which doesn't mention
BTRFS. (and is conceivably filesystem independent - I think XFS supports
it?)

Re: Btrfs clone support in copy operations

[Paul Eggert]

Thanks for the suggestion. I've created a bug report for this 
suggestion, Bug#23904. You can view its current status here:

http://bugs.gnu.org/23904

or add to the thread by sending email to 23904@debbugs.gnu.org.