netdev - [PATCH net] vsock/virtio: fix "comparison of distinct pointer types lacks a cast" warning

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Message-ID: <20231206164143.281107-1-sgarzare@redhat.com>
Date: Wed,  6 Dec 2023 17:41:43 +0100
From: Stefano Garzarella <sgarzare@...hat.com>
To: netdev@...r.kernel.org
Cc: Jakub Kicinski <kuba@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	virtualization@...ts.linux.dev,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Arseniy Krasnov <avkrasnov@...utedevices.com>,
	Stefano Garzarella <sgarzare@...hat.com>,
	kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Stefan Hajnoczi <stefanha@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Paolo Abeni <pabeni@...hat.com>
Subject: [PATCH net] vsock/virtio: fix "comparison of distinct pointer types lacks a cast" warning

After backporting commit 581512a6dc93 ("vsock/virtio: MSG_ZEROCOPY
flag support") in CentOS Stream 9, CI reported the following error:

    In file included from ./include/linux/kernel.h:17,
                     from ./include/linux/list.h:9,
                     from ./include/linux/preempt.h:11,
                     from ./include/linux/spinlock.h:56,
                     from net/vmw_vsock/virtio_transport_common.c:9:
    net/vmw_vsock/virtio_transport_common.c: In function ‘virtio_transport_can_zcopy‘:
    ./include/linux/minmax.h:20:35: error: comparison of distinct pointer types lacks a cast [-Werror]
       20 |         (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
          |                                   ^~
    ./include/linux/minmax.h:26:18: note: in expansion of macro ‘__typecheck‘
       26 |                 (__typecheck(x, y) && __no_side_effects(x, y))
          |                  ^~~~~~~~~~~
    ./include/linux/minmax.h:36:31: note: in expansion of macro ‘__safe_cmp‘
       36 |         __builtin_choose_expr(__safe_cmp(x, y), \
          |                               ^~~~~~~~~~
    ./include/linux/minmax.h:45:25: note: in expansion of macro ‘__careful_cmp‘
       45 | #define min(x, y)       __careful_cmp(x, y, <)
          |                         ^~~~~~~~~~~~~
    net/vmw_vsock/virtio_transport_common.c:63:37: note: in expansion of macro ‘min‘
       63 |                 int pages_to_send = min(pages_in_iov, MAX_SKB_FRAGS);

We could solve it by using min_t(), but this operation seems entirely
unnecessary, because we also pass MAX_SKB_FRAGS to iov_iter_npages(),
which performs almost the same check, returning at most MAX_SKB_FRAGS
elements. So, let's eliminate this unnecessary comparison.

Fixes: 581512a6dc93 ("vsock/virtio: MSG_ZEROCOPY flag support")
Cc: avkrasnov@...utedevices.com
Signed-off-by: Stefano Garzarella <sgarzare@...hat.com>
---
 net/vmw_vsock/virtio_transport_common.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
index f6dc896bf44c..c8e162c9d1df 100644
--- a/net/vmw_vsock/virtio_transport_common.c
+++ b/net/vmw_vsock/virtio_transport_common.c
@@ -59,8 +59,7 @@ static bool virtio_transport_can_zcopy(const struct virtio_transport *t_ops,
 	t_ops = virtio_transport_get_ops(info->vsk);
 
 	if (t_ops->can_msgzerocopy) {
-		int pages_in_iov = iov_iter_npages(iov_iter, MAX_SKB_FRAGS);
-		int pages_to_send = min(pages_in_iov, MAX_SKB_FRAGS);
+		int pages_to_send = iov_iter_npages(iov_iter, MAX_SKB_FRAGS);
 
 		/* +1 is for packet header. */
 		return t_ops->can_msgzerocopy(pages_to_send + 1);
-- 
2.43.0