should the svc_xprt_get called after the object assigned to a global variable？

should the svc_xprt_get called after the object assigned to a global variable？

[易林]

Hi, all:
    when analyzing the v5.1 source code, I notice that in function nfsd4_process_cb_update, 
the object c->cn_xprt assigned to a local variable conn.cb_xprt with a refcount increased:
      if (c) {
		svc_xprt_get(c->cn_xprt);
		conn.cb_xprt = c->cn_xprt;
		ses = c->cn_session;
	}

and the variable conn.cb_xprt will be assigned to a global object clp->cl_cb_conn.cb_xprt 
in callee setup_callback_client with a condition that clp->cl_minorversion != 0:

       if (clp->cl_minorversion == 0) {
		if (!clp->cl_cred.cr_principal &&
				(clp->cl_cred.cr_flavor >= RPC_AUTH_GSS_KRB5))
			return -EINVAL;
		args.client_name = clp->cl_cred.cr_principal;
		args.prognumber	= conn->cb_prog;
		args.protocol = XPRT_TRANSPORT_TCP;
		args.authflavor = clp->cl_cred.cr_flavor;
		clp->cl_cb_ident = conn->cb_ident;
	} else {
		if (!conn->cb_xprt)
			return -EINVAL;
		clp->cl_cb_conn.cb_xprt = conn->cb_xprt;
		clp->cl_cb_session = ses;
		args.bc_xprt = conn->cb_xprt;
		args.prognumber = clp->cl_cb_session->se_cb_prog;
		args.protocol = conn->cb_xprt->xpt_class->xcl_ident |
				XPRT_TRANSPORT_BC;
		args.authflavor = ses->se_cb_sec.flavor;
	}

what if the cl_minorversion equals 0 ? the c->cn_xprt's refcount will increased without a assignment. 
Can it be ensured that the cl_minorversion won't be zero with the refcount increment?

Best Regards

Lin Yi

Re: should the svc_xprt_get called after the object assigned to a global variable？

[J. Bruce Fields]

On Sun, Apr 07, 2019 at 07:40:43PM +0800, 易林 wrote:
> Hi, all:
>     when analyzing the v5.1 source code, I notice that in function nfsd4_process_cb_update, 
> the object c->cn_xprt assigned to a local variable conn.cb_xprt with a refcount increased:
>       if (c) {
> 		svc_xprt_get(c->cn_xprt);
> 		conn.cb_xprt = c->cn_xprt;
> 		ses = c->cn_session;
> 	}
> 
> and the variable conn.cb_xprt will be assigned to a global object clp->cl_cb_conn.cb_xprt 
> in callee setup_callback_client with a condition that clp->cl_minorversion != 0:
> 
>        if (clp->cl_minorversion == 0) {
> 		if (!clp->cl_cred.cr_principal &&
> 				(clp->cl_cred.cr_flavor >= RPC_AUTH_GSS_KRB5))
> 			return -EINVAL;
> 		args.client_name = clp->cl_cred.cr_principal;
> 		args.prognumber	= conn->cb_prog;
> 		args.protocol = XPRT_TRANSPORT_TCP;
> 		args.authflavor = clp->cl_cred.cr_flavor;
> 		clp->cl_cb_ident = conn->cb_ident;
> 	} else {
> 		if (!conn->cb_xprt)
> 			return -EINVAL;
> 		clp->cl_cb_conn.cb_xprt = conn->cb_xprt;
> 		clp->cl_cb_session = ses;
> 		args.bc_xprt = conn->cb_xprt;
> 		args.prognumber = clp->cl_cb_session->se_cb_prog;
> 		args.protocol = conn->cb_xprt->xpt_class->xcl_ident |
> 				XPRT_TRANSPORT_BC;
> 		args.authflavor = ses->se_cb_sec.flavor;
> 	}
> 
> what if the cl_minorversion equals 0 ? the c->cn_xprt's refcount will increased without a assignment. 
> Can it be ensured that the cl_minorversion won't be zero with the refcount increment?

Sessions were introduced with NFSv4.1, __nfsd4_find_backchannel should
always find clp->cl_sessions empty in the 4.0 case.

So I think it's OK.  Not the clearest code ever, though.  I wonder if it
would make sense to separate the 4.0 and 4.1 codepaths earlier on, given
how little code they share.

--b.

should the svc_xprt_get called after the object assigned to a global variable？

[易林]

Hi, all:
    when analyzing the v5.1 source code, I notice that in function nfsd4_process_cb_update, 
the object c->cn_xprt assigned to a local variable conn.cb_xprt with a refcount increased:
      if (c) {
		svc_xprt_get(c->cn_xprt);
		conn.cb_xprt = c->cn_xprt;
		ses = c->cn_session;
	}

and the variable conn.cb_xprt will be assigned to a global object clp->cl_cb_conn.cb_xprt 
in callee setup_callback_client with a condition that clp->cl_minorversion != 0:

       if (clp->cl_minorversion == 0) {
		if (!clp->cl_cred.cr_principal &&
				(clp->cl_cred.cr_flavor >= RPC_AUTH_GSS_KRB5))
			return -EINVAL;
		args.client_name = clp->cl_cred.cr_principal;
		args.prognumber	= conn->cb_prog;
		args.protocol = XPRT_TRANSPORT_TCP;
		args.authflavor = clp->cl_cred.cr_flavor;
		clp->cl_cb_ident = conn->cb_ident;
	} else {
		if (!conn->cb_xprt)
			return -EINVAL;
		clp->cl_cb_conn.cb_xprt = conn->cb_xprt;
		clp->cl_cb_session = ses;
		args.bc_xprt = conn->cb_xprt;
		args.prognumber = clp->cl_cb_session->se_cb_prog;
		args.protocol = conn->cb_xprt->xpt_class->xcl_ident |
				XPRT_TRANSPORT_BC;
		args.authflavor = ses->se_cb_sec.flavor;
	}

what if the cl_minorversion equals 0 ? the c->cn_xprt's refcount will increased without a assignment. 
Can it be ensured that the cl_minorversion won't be zero with the refcount increment?

Best Regards

Lin Yi