linux-kernel - [PATCH v2] IB/mlx4: silence GCC warning

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Date:	Thu, 21 Feb 2013 10:02:57 +0100
From:	Paul Bolle <pebolle@...cali.nl>
To:	Roland Dreier <roland@...nel.org>,
	Sean Hefty <sean.hefty@...el.com>,
	Hal Rosenstock <hal.rosenstock@...il.com>,
	Jack Morgenstein <jackm@....mellanox.co.il>,
	Bart Van Assche <bvanassche@....org>
Cc:	linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...nel.org>
Subject: [PATCH v2] IB/mlx4: silence GCC warning

Building qp.o (part of the "Mellanox ConnectX HCA support" driver)
triggers this GCC warning:
    drivers/infiniband/hw/mlx4/qp.c: In function ‘mlx4_ib_post_send’:
    drivers/infiniband/hw/mlx4/qp.c:1862:30: warning: ‘vlan’ may be used uninitialized in this function [-Wmaybe-uninitialized]
    drivers/infiniband/hw/mlx4/qp.c:1752:6: note: ‘vlan’ was declared here

Looking at the code it is clear 'vlan' is only set and used if 'is_eth'
is non-zero. But by, basically, initializing 'vlan' to 0xffff, instead
of the equivalent of initializing 'is_vlan' to zero, we can make this
warning go away.

Signed-off-by: Paul Bolle <pebolle@...cali.nl>
---
0) Jack wanted to use uninitialized_var() after I posted the first
version of this trivial patch. I suggested to see what happened with
Ingo's idea to remove uninitialized_var() entirely. Nothing seems to
have happened, so I decided to try a different approach.

1) Still compile tested only, but now against v3.8.

 drivers/infiniband/hw/mlx4/qp.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/infiniband/hw/mlx4/qp.c b/drivers/infiniband/hw/mlx4/qp.c
index 19e0637..512fde3 100644
--- a/drivers/infiniband/hw/mlx4/qp.c
+++ b/drivers/infiniband/hw/mlx4/qp.c
@@ -1747,9 +1747,9 @@ static int build_mlx_header(struct mlx4_ib_sqp *sqp, struct ib_send_wr *wr,
 	int spc;
 	int i;
 	int is_eth;
-	int is_vlan = 0;
+	int is_vlan;
 	int is_grh;
-	u16 vlan;
+	u16 vlan = 0xffff; /* invalid vlan id */
 	int err = 0;
 
 	send_size = 0;
@@ -1778,8 +1778,8 @@ static int build_mlx_header(struct mlx4_ib_sqp *sqp, struct ib_send_wr *wr,
 		}
 
 		vlan = rdma_get_vlan_id(&sgid);
-		is_vlan = vlan < 0x1000;
 	}
+	is_vlan = vlan < 0x1000;
 	ib_ud_header_init(send_size, !is_eth, is_eth, is_vlan, is_grh, 0, &sqp->ud_header);
 
 	if (!is_eth) {
-- 
1.7.11.7

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