linux-kernel - [PATCH 5/6] wifi: ath10k: use flexible array in struct wmi_tdls_peer

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Message-ID: <20231213-wmi_host_mem_chunks_flexarray-v1-5-92922d92fa2c@quicinc.com>
Date:   Wed, 13 Dec 2023 09:06:43 -0800
From:   Jeff Johnson <quic_jjohnson@...cinc.com>
To:     Kalle Valo <kvalo@...nel.org>,
        Jeff Johnson <quic_jjohnson@...cinc.com>
CC:     Kees Cook <keescook@...omium.org>,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        <ath10k@...ts.infradead.org>, <linux-wireless@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: [PATCH 5/6] wifi: ath10k: use flexible array in struct
 wmi_tdls_peer_capabilities

Currently struct wmi_tdls_peer_capabilities defines:
	struct wmi_channel peer_chan_list[1];

Per the guidance in [1] this should be a flexible array, and at one
point Gustavo was trying to fix this [2], but had questions about the
correct behavior when the associated peer_chan_len is 0.

I have been unable to determine if firmware requires that at least one
record be present even if peer_chan_len is 0. But since that is the
current behavior, follow the example from [3] and replace the
one-element array with a union that contains both a flexible array and
a single instance of the array element. This results in a struct that
has the same footprint as the original, so no other driver changes are
required.

No functional changes, compile tested only.

[1] https://docs.kernel.org/process/deprecated.html#zero-length-and-one-element-arrays
[2] https://lore.kernel.org/linux-wireless/626ae2e7-66f8-423b-b17f-e75c1a6d29b3@embeddedor.com/
[3] https://lore.kernel.org/linux-wireless/202308301529.AC90A9EF98@keescook/

Signed-off-by: Jeff Johnson <quic_jjohnson@...cinc.com>
---
 drivers/net/wireless/ath/ath10k/wmi.h | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/net/wireless/ath/ath10k/wmi.h b/drivers/net/wireless/ath/ath10k/wmi.h
index e16410e348ca..b64b6e214bae 100644
--- a/drivers/net/wireless/ath/ath10k/wmi.h
+++ b/drivers/net/wireless/ath/ath10k/wmi.h
@@ -7162,7 +7162,13 @@ struct wmi_tdls_peer_capabilities {
 	__le32 is_peer_responder;
 	__le32 pref_offchan_num;
 	__le32 pref_offchan_bw;
-	struct wmi_channel peer_chan_list[1];
+	union {
+		/* to match legacy implementation allocate room for
+		 * at least one record even if peer_chan_len is 0
+		 */
+		struct wmi_channel peer_chan_min_allocation;
+		DECLARE_FLEX_ARRAY(struct wmi_channel, peer_chan_list);
+	};
 } __packed;
 
 struct wmi_10_4_tdls_peer_update_cmd {

-- 
2.42.0