Introduce cifs_copy_file_range()

The earlier changes to copy range for cifs unintentionally disabled the more
common form of server side copy.

The patch introduces the file_operations helper cifs_copy_file_range()
which is used by the syscall copy_file_range. The new file operations
helper allows us to perform server side copies for SMB2.0 and 2.1
servers as well as SMB 3.0+ servers which do not support the ioctl
FSCTL_DUPLICATE_EXTENTS_TO_FILE.

The new helper uses the ioctl FSCTL_SRV_COPYCHUNK_WRITE to perform
server side copies. The helper is called by vfs_copy_file_range() only
once an attempt to clone the file using the ioctl
FSCTL_DUPLICATE_EXTENTS_TO_FILE has failed.

Signed-off-by: Sachin Prabhu <sprabhu@redhat.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>
CC: Stable  <stable@vger.kernel.org>
Signed-off-by: Steve French <smfrench@gmail.com>

fs/cifs/smb2ops.c

@@ -592,7 +592,7 @@ req_res_key_exit:
 	return rc;
 }
 
-static int
+static ssize_t
 smb2_copychunk_range(const unsigned int xid,
 			struct cifsFileInfo *srcfile,
 			struct cifsFileInfo *trgtfile, u64 src_off,
@@ -605,6 +605,7 @@ smb2_copychunk_range(const unsigned int xid,
 	struct cifs_tcon *tcon;
 	int chunks_copied = 0;
 	bool chunk_sizes_updated = false;
+	ssize_t bytes_written, total_bytes_written = 0;
 
 	pcchunk = kmalloc(sizeof(struct copychunk_ioctl), GFP_KERNEL);
 
@@ -669,14 +670,16 @@ smb2_copychunk_range(const unsigned int xid,
 			}
 			chunks_copied++;
 
-			src_off += le32_to_cpu(retbuf->TotalBytesWritten);
-			dest_off += le32_to_cpu(retbuf->TotalBytesWritten);
-			len -= le32_to_cpu(retbuf->TotalBytesWritten);
+			bytes_written = le32_to_cpu(retbuf->TotalBytesWritten);
+			src_off += bytes_written;
+			dest_off += bytes_written;
+			len -= bytes_written;
+			total_bytes_written += bytes_written;
 
-			cifs_dbg(FYI, "Chunks %d PartialChunk %d Total %d\n",
+			cifs_dbg(FYI, "Chunks %d PartialChunk %d Total %zu\n",
 				le32_to_cpu(retbuf->ChunksWritten),
 				le32_to_cpu(retbuf->ChunkBytesWritten),
-				le32_to_cpu(retbuf->TotalBytesWritten));
+				bytes_written);
 		} else if (rc == -EINVAL) {
 			if (ret_data_len != sizeof(struct copychunk_ioctl_rsp))
 				goto cchunk_out;
@@ -713,7 +716,10 @@ smb2_copychunk_range(const unsigned int xid,
 cchunk_out:
 	kfree(pcchunk);
 	kfree(retbuf);
-	return rc;
+	if (rc)
+		return rc;
+	else
+		return total_bytes_written;
 }
 
 static int