[libvirt] [PATCHv2 1/2] storage: introduce btrfsCloneFile() for COW copy

[Chen Hanxiao]

Signed-off-by: Chen Hanxiao <chenhanxiao at cn.fujitsu.com>
---
 configure.ac                  | 12 ++++++++++++
 src/storage/storage_backend.c | 24 ++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/configure.ac b/configure.ac
index f370475..2498389 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2175,6 +2175,18 @@ fi
 AM_CONDITIONAL([WITH_HYPERV], [test "$with_hyperv" = "yes"])
 
 
+dnl
+dnl check for kernel headers required by btrfs ioctl
+dnl
+if test "$with_linux" = "yes"; then
+    have_btrfs=no
+    AC_CHECK_HEADER([linux/btrfs.h],[have_btrfs=yes])
+    if test "${have_btrfs}" = yes; then
+        AC_DEFINE([HAVE_BTRFS_IOC_CLONE], 1,
+                  [whether have btrfs CoW clone ioctl])
+    fi
+fi
+
 dnl Allow perl/python overrides
 AC_PATH_PROGS([PYTHON], [python2 python])
 AC_PATH_PROG([PERL], [perl])
diff --git a/src/storage/storage_backend.c b/src/storage/storage_backend.c
index b990a82..d2a664b 100644
--- a/src/storage/storage_backend.c
+++ b/src/storage/storage_backend.c
@@ -46,6 +46,10 @@
 # include <selinux/selinux.h>
 #endif
 
+#if HAVE_BTRFS_IOC_CLONE
+# include <linux/btrfs.h>
+#endif
+
 #include "datatypes.h"
 #include "virerror.h"
 #include "viralloc.h"
@@ -156,6 +160,26 @@ enum {
 #define READ_BLOCK_SIZE_DEFAULT  (1024 * 1024)
 #define WRITE_BLOCK_SIZE_DEFAULT (4 * 1024)
 
+/*
+ * Perform the O(1) btrfs clone operation, if possible.
+ * Upon success, return 0.  Otherwise, return -1 and set errno.
+ */
+#if defined(HAVE_BTRFS_IOC_CLONE)
+static inline int
+btrfsCloneFile(int dest_fd, int src_fd)
+{
+    return ioctl(dest_fd, BTRFS_IOC_CLONE, src_fd);
+}
+#else
+static inline int
+btrfsCloneFile(int dest_fd ATTRIBUTE_UNUSED,
+               int src_fd ATTRIBUTE_UNUSED)
+{
+    errno = ENOTSUP;
+    return -1;
+}
+#endif
+
 static int ATTRIBUTE_NONNULL(2)
 virStorageBackendCopyToFD(virStorageVolDefPtr vol,
                           virStorageVolDefPtr inputvol,
-- 
2.1.0