Implementation of block cloning for ZFS

Block Cloning allows to manually clone a file (or a subset of its
blocks) into another (or the same) file by just creating additional
references to the data blocks without copying the data itself.
Those references are kept in the Block Reference Tables (BRTs).

The whole design of block cloning is documented in module/zfs/brt.c.

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Christian Schwarz <christian.schwarz@nutanix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Rich Ercolani <rincebrain@gmail.com>
Signed-off-by: Pawel Jakub Dawidek <pawel@dawidek.net>
Closes #13392

include/os/freebsd/zfs/sys/zfs_znode_impl.h

@@ -119,7 +119,8 @@ typedef struct zfs_soft_state {
 #define	zn_has_cached_data(zp, start, end) \
     vn_has_cached_data(ZTOV(zp))
 #define	zn_flush_cached_data(zp, sync)	vn_flush_cached_data(ZTOV(zp), sync)
-#define	zn_rlimit_fsize(zp, uio) \
+#define	zn_rlimit_fsize(size)		zfs_rlimit_fsize(size)
+#define	zn_rlimit_fsize_uio(zp, uio) \
     vn_rlimit_fsize(ZTOV(zp), GET_UIO_STRUCT(uio), zfs_uio_td(uio))
 
 /* Called on entry to each ZFS vnode and vfs operation  */
@@ -179,6 +180,8 @@ extern zil_replay_func_t *const zfs_replay_vector[TX_MAX_TYPE];
 
 extern int zfs_znode_parent_and_name(struct znode *zp, struct znode **dzpp,
     char *buf);
+
+extern int zfs_rlimit_fsize(off_t fsize);
 #ifdef	__cplusplus
 }
 #endif