Re: [PATCH v4 1/2] sunrpc: fix unused variable warnings by using no_printk

[Andrew Lunn]

> HI all,
> I've also identified the cause of the build error in fs/nfsd/nfsfh.c
> reported by syzbot [1]. The "use of undeclared identifier 'buf'" occurs
> because buf is only declared within the RPC_IFDEBUG macro,
> which is removed when CONFIG_SUNRPC_DEBUG is disabled.
> To fix this, I will follow the pattern used in net/sunrpc/xprtrdma/
> svc_rdma_transport.c by wrapping the dprintk call that references
> buf within an #if IS_ENABLED(CONFIG_SUNRPC_DEBUG) block.

Please try to avoid adding such #if code. Compile testing does not
work as well if there are millions of #if def combinations. Ideally we
want the stub functions to allow as much as possible to be compiled,
and then let the optimizer throw it out because it is unreachable.

> 
> static struct svc_xprt *svc_rdma_accept(struct svc_xprt *xprt)
> {
> ....
> RPC_IFDEBUG(struct sockaddr *sap);
> ...
> #if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
> dprintk("svcrdma: new connection accepted on device %s:\n", dev->name);
> sap = (struct sockaddr *)&newxprt->sc_cm_id->route.addr.src_addr;
> dprintk(" local address : %pIS:%u\n", sap, rpc_get_port(sap));
> sap = (struct sockaddr *)&newxprt->sc_cm_id->route.addr.dst_addr;
> dprintk(" remote address : %pIS:%u\n", sap, rpc_get_port(sap));
> dprintk(" max_sge : %d\n", newxprt->sc_max_send_sges);
> dprintk(" sq_depth : %d\n", newxprt->sc_sq_depth);
> dprintk(" rdma_rw_ctxs : %d\n", ctxts);
> dprintk(" max_requests : %d\n", newxprt->sc_max_requests);
> dprintk(" ord : %d\n", conn_param.initiator_depth);
> #endif
> ...
> }
> 
> The refactor in fs/nfsd/nfsfh.c will look like this:
> 
> static __be32 nfsd_setuser_and_check_port(struct svc_rqst *rqstp,
> struct svc_cred *cred,
> struct svc_export *exp)
> {
>     /* Check if the request originated from a secure port. */
>     if (rqstp && !nfsd_originating_port_ok(rqstp, cred, exp)) {
>        RPC_IFDEBUG(char buf[RPC_MAX_ADDRBUFLEN]);
> +#if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
>        dprintk("nfsd: request from insecure port %s!\n",
>        svc_print_addr(rqstp, buf, sizeof(buf)));
> +#endif

In this case, now dprintk() uses it arguments, i think you can drop
the RPC_IFDEBUG() and always have buf. This code then gets
compiled. Ask make to produce fs/nfsd/nfsfh.lst and see if it
generated any code for this, or has it optimized it out.

	  Andrew