Add reflink copy over SMB3.11 with new FSCTL_DUPLICATE_EXTENTS

Getting fantastic copy performance with cp --reflink over SMB3.11
 using the new FSCTL_DUPLICATE_EXTENTS.

 This FSCTL was added in the SMB3.11 dialect (testing was
 against REFS file system) so have put it as a 3.11 protocol
 specific operation ("vers=3.1.1" on the mount).  Tested at
 the SMB3 plugfest in Redmond.

 It depends on the new FS Attribute (BLOCK_REFCOUNTING) which
 is used to advertise support for the ability to do this ioctl
 (if you can support multiple files pointing to the same block
 than this refcounting ability or equivalent is needed to
 support the new reflink-like duplicate extent SMB3 ioctl.

Signed-off-by: Steve French <steve.french@primarydata.com>

fs/cifs/ioctl.c

@@ -31,12 +31,14 @@
 #include "cifsproto.h"
 #include "cifs_debug.h"
 #include "cifsfs.h"
+#include <linux/btrfs.h>
 
 #define CIFS_IOCTL_MAGIC	0xCF
 #define CIFS_IOC_COPYCHUNK_FILE	_IOW(CIFS_IOCTL_MAGIC, 3, int)
 
 static long cifs_ioctl_clone(unsigned int xid, struct file *dst_file,
-			unsigned long srcfd, u64 off, u64 len, u64 destoff)
+			unsigned long srcfd, u64 off, u64 len, u64 destoff,
+			bool dup_extents)
 {
 	int rc;
 	struct cifsFileInfo *smb_file_target = dst_file->private_data;
@@ -109,9 +111,14 @@ static long cifs_ioctl_clone(unsigned int xid, struct file *dst_file,
 	truncate_inode_pages_range(&target_inode->i_data, destoff,
 				   PAGE_CACHE_ALIGN(destoff + len)-1);
 
-	if (target_tcon->ses->server->ops->clone_range)
+	if (dup_extents && target_tcon->ses->server->ops->duplicate_extents)
+		rc = target_tcon->ses->server->ops->duplicate_extents(xid,
+			smb_file_src, smb_file_target, off, len, destoff);
+	else if (!dup_extents && target_tcon->ses->server->ops->clone_range)
 		rc = target_tcon->ses->server->ops->clone_range(xid,
 			smb_file_src, smb_file_target, off, len, destoff);
+	else
+		rc = -EOPNOTSUPP;
 
 	/* force revalidate of size and timestamps of target file now
 	   that target is updated on the server */
@@ -205,7 +212,10 @@ long cifs_ioctl(struct file *filep, unsigned int command, unsigned long arg)
 			}
 			break;
 		case CIFS_IOC_COPYCHUNK_FILE:
-			rc = cifs_ioctl_clone(xid, filep, arg, 0, 0, 0);
+			rc = cifs_ioctl_clone(xid, filep, arg, 0, 0, 0, false);
+			break;
+		case BTRFS_IOC_CLONE:
+			rc = cifs_ioctl_clone(xid, filep, arg, 0, 0, 0, true);
 			break;
 		default:
 			cifs_dbg(FYI, "unsupported ioctl\n");