zfs: Add vfs.zfs.bclone_enabled sysctl.

Keep block cloning disabled by default for now, but allow to enable and
use it after setting vfs.zfs.bclone_enabled to 1, so people can easily
try it.

Approved by:	oshogbo
Reviewed by:	mm, oshogbo
Differential Revision:	https://reviews.freebsd.org/D39613

sys/contrib/openzfs/include/os/freebsd/zfs/sys/zfs_vfsops_os.h

@@ -287,6 +287,7 @@ typedef struct zfid_long {
 
 extern uint_t zfs_fsyncer_key;
 extern int zfs_super_owner;
+extern int zfs_bclone_enabled;
 
 extern void zfs_init(void);
 extern void zfs_fini(void);

sys/contrib/openzfs/module/os/freebsd/zfs/zfs_vfsops.c

@@ -89,6 +89,10 @@ int zfs_debug_level;
 SYSCTL_INT(_vfs_zfs, OID_AUTO, debug, CTLFLAG_RWTUN, &zfs_debug_level, 0,
 	"Debug level");
 
+int zfs_bclone_enabled;
+SYSCTL_INT(_vfs_zfs, OID_AUTO, bclone_enabled, CTLFLAG_RWTUN,
+	&zfs_bclone_enabled, 0, "Enable block cloning");
+
 struct zfs_jailparam {
 	int mount_snapshot;
 };

sys/contrib/openzfs/module/os/freebsd/zfs/zfs_vnops_os.c

@@ -6214,7 +6214,6 @@ zfs_deallocate(struct vop_deallocate_args *ap)
 }
 #endif
 
-#if 0
 #ifndef _SYS_SYSPROTO_H_
 struct vop_copy_file_range_args {
 	struct vnode *a_invp;
@@ -6245,6 +6244,11 @@ zfs_freebsd_copy_file_range(struct vop_copy_file_range_args *ap)
 	int error;
 	uint64_t len = *ap->a_lenp;
 
+	if (!zfs_bclone_enabled) {
+		mp = NULL;
+		goto bad_write_fallback;
+	}
+
 	/*
 	 * TODO: If offset/length is not aligned to recordsize, use
 	 * vn_generic_copy_file_range() on this fragment.
@@ -6310,7 +6314,6 @@ zfs_freebsd_copy_file_range(struct vop_copy_file_range_args *ap)
 	    ap->a_incred, ap->a_outcred, ap->a_fsizetd);
 	return (error);
 }
-#endif
 
 struct vop_vector zfs_vnodeops;
 struct vop_vector zfs_fifoops;
@@ -6375,6 +6378,7 @@ struct vop_vector zfs_vnodeops = {
 #if __FreeBSD_version >= 1400043
 	.vop_add_writecount =	vop_stdadd_writecount_nomsync,
 #endif
+	.vop_copy_file_range =	zfs_freebsd_copy_file_range,
 };
 VFS_VOP_VECTOR_REGISTER(zfs_vnodeops);