[PATCH v5 1/2] sunrpc: simplify dfprintk macros and fix nfsd build error

[Sean Chang <seanwascoding@gmail.com>]

When CONFIG_SUNRPC_DEBUG is disabled, the dfprintk() macros currently
expand to empty do-while loops. This causes variables used solely
within these calls to appear unused, triggering -Wunused-variable
warnings.

Following David Laight's suggestion, simplify the macro definitions by
removing the unnecessary 'fmt' argument and using no_printk(__VA_ARGS__)
directly. This ensures the compiler performs type checking and "sees"
the variables, silencing the warnings without emitting any code.

Additionally, fix a build error in fs/nfsd/nfsfh.c reported by syzbot.
In nfsd_setuser_and_check_port(), the variable 'buf' is conditionally
defined via RPC_IFDEBUG. Since no_printk() now performs type checking,
it triggers an 'undeclared identifier' error when debug is disabled.
Wrap the dprintk call in an #if block to synchronize its lifecycle
with 'buf', following the pattern in svc_rdma_transport.c.

Link: https://lore.kernel.org/all/69a2e269.050a0220.3a55be.003e.GAE@google.com/
Suggested-by: Andrew Lunn <andrew@lunn.ch>
Suggested-by: David Laight <david.laight.linux@gmail.com>
Signed-off-by: Sean Chang <seanwascoding@gmail.com>
---
 fs/nfsd/nfsfh.c              | 2 ++
 include/linux/sunrpc/debug.h | 4 ++--
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
index ed85dd43da18..f7386fd483a6 100644
--- a/fs/nfsd/nfsfh.c
+++ b/fs/nfsd/nfsfh.c
@@ -106,8 +106,10 @@ static __be32 nfsd_setuser_and_check_port(struct svc_rqst *rqstp,
 	/* 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
 		return nfserr_perm;
 	}
 
diff --git a/include/linux/sunrpc/debug.h b/include/linux/sunrpc/debug.h
index eb4bd62df319..cb33c7e1f370 100644
--- a/include/linux/sunrpc/debug.h
+++ b/include/linux/sunrpc/debug.h
@@ -52,8 +52,8 @@ do {									\
 # define RPC_IFDEBUG(x)		x
 #else
 # define ifdebug(fac)		if (0)
-# define dfprintk(fac, fmt, ...)	do {} while (0)
-# define dfprintk_rcu(fac, fmt, ...)	do {} while (0)
+# define dfprintk(fac, ...)		no_printk(__VA_ARGS__)
+# define dfprintk_rcu(fac, ...)	no_printk(__VA_ARGS__)
 # define RPC_IFDEBUG(x)
 #endif
 
-- 
2.34.1