[PATCH 1/2] Introduce btrfsCloneFile for btrfs COW copy

[Chen Hanxiao <chenhanxiao@xxxxxxxxxxxxxx>]

Signed-off-by: Chen Hanxiao <chenhanxiao@xxxxxxxxxxxxxx>
---
 src/storage/storage_backend.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/src/storage/storage_backend.c b/src/storage/storage_backend.c
index b990a82..5ce3566 100644
--- a/src/storage/storage_backend.c
+++ b/src/storage/storage_backend.c
@@ -156,6 +156,32 @@ 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(BTRFS_IOCTL_MAGIC)
+# define BTRFS_IOCTL_MAGIC 0x94
+#endif
+
+#define BTRFS_IOC_CLONE _IOW (BTRFS_IOCTL_MAGIC, 9, int)
+
+#if defined(__linux__)
+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,
-- 
1.9.3

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