net: ethtool: Avoid thousands of -Wflex-array-member-not-at-end warnings

-Wflex-array-member-not-at-end was introduced in GCC-14, and we are
getting ready to enable it, globally.

Change the type of the middle struct member currently causing trouble from
`struct ethtool_link_settings` to `struct ethtool_link_settings_hdr`.

Additionally, update the type of some variables in various functions that
don't access the flexible-array member, changing them to the newly created
`struct ethtool_link_settings_hdr`. These changes are needed because the
type of the conflicting middle members changed. So, those instances that
expect the type to be `struct ethtool_link_settings` should be adjusted to
the newly created type `struct ethtool_link_settings_hdr`.

Also, adjust variable declarations to follow the reverse xmas tree
convention.

Fix 3338 of the following -Wflex-array-member-not-at-end warnings:

include/linux/ethtool.h:214:38: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://patch.msgid.link/0bc2809fe2a6c11dd4c8a9a10d9bd65cccdb559b.1730238285.git.gustavoars@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

3 files changed, 16 insertions, 12 deletions

diff --git a/net/ethtool/ioctl.c b/net/ethtool/ioctl.c
index 5cc131cdb1bc..7da94e26ced6 100644
--- a/net/ethtool/ioctl.c
+++ b/net/ethtool/ioctl.c
@@ -425,7 +425,7 @@ convert_link_ksettings_to_legacy_settings(
 
 /* layout of the struct passed from/to userland */
 struct ethtool_link_usettings {
-	struct ethtool_link_settings base;
+	struct ethtool_link_settings_hdr base;
 	struct {
 		__u32 supported[__ETHTOOL_LINK_MODE_MASK_NU32];
 		__u32 advertising[__ETHTOOL_LINK_MODE_MASK_NU32];
diff --git a/net/ethtool/linkinfo.c b/net/ethtool/linkinfo.c
index 30b8ce275159..2d5bc57160be 100644
--- a/net/ethtool/linkinfo.c
+++ b/net/ethtool/linkinfo.c
@@ -8,9 +8,9 @@ struct linkinfo_req_info {
 };
 
 struct linkinfo_reply_data {
-	struct ethnl_reply_data		base;
-	struct ethtool_link_ksettings	ksettings;
-	struct ethtool_link_settings	*lsettings;
+	struct ethnl_reply_data			base;
+	struct ethtool_link_ksettings		ksettings;
+	struct ethtool_link_settings_hdr	*lsettings;
 };
 
 #define LINKINFO_REPDATA(__reply_base) \
@@ -98,7 +98,7 @@ static int
 ethnl_set_linkinfo(struct ethnl_req_info *req_info, struct genl_info *info)
 {
 	struct ethtool_link_ksettings ksettings = {};
-	struct ethtool_link_settings *lsettings;
+	struct ethtool_link_settings_hdr *lsettings;
 	struct net_device *dev = req_info->dev;
 	struct nlattr **tb = info->attrs;
 	bool mod = false;
diff --git a/net/ethtool/linkmodes.c b/net/ethtool/linkmodes.c
index 259cd9ef1f2a..17e49cf89f03 100644
--- a/net/ethtool/linkmodes.c
+++ b/net/ethtool/linkmodes.c
@@ -11,10 +11,10 @@ struct linkmodes_req_info {
 };
 
 struct linkmodes_reply_data {
-	struct ethnl_reply_data		base;
-	struct ethtool_link_ksettings	ksettings;
-	struct ethtool_link_settings	*lsettings;
-	bool				peer_empty;
+	struct ethnl_reply_data			base;
+	struct ethtool_link_ksettings		ksettings;
+	struct ethtool_link_settings_hdr	*lsettings;
+	bool					peer_empty;
 };
 
 #define LINKMODES_REPDATA(__reply_base) \
@@ -62,10 +62,12 @@ static int linkmodes_reply_size(const struct ethnl_req_info *req_base,
 {
 	const struct linkmodes_reply_data *data = LINKMODES_REPDATA(reply_base);
 	const struct ethtool_link_ksettings *ksettings = &data->ksettings;
-	const struct ethtool_link_settings *lsettings = &ksettings->base;
 	bool compact = req_base->flags & ETHTOOL_FLAG_COMPACT_BITSETS;
+	const struct ethtool_link_settings_hdr *lsettings;
 	int len, ret;
 
+	lsettings = &ksettings->base;
+
 	len = nla_total_size(sizeof(u8)) /* LINKMODES_AUTONEG */
 		+ nla_total_size(sizeof(u32)) /* LINKMODES_SPEED */
 		+ nla_total_size(sizeof(u32)) /* LINKMODES_LANES */
@@ -103,10 +105,12 @@ static int linkmodes_fill_reply(struct sk_buff *skb,
 {
 	const struct linkmodes_reply_data *data = LINKMODES_REPDATA(reply_base);
 	const struct ethtool_link_ksettings *ksettings = &data->ksettings;
-	const struct ethtool_link_settings *lsettings = &ksettings->base;
 	bool compact = req_base->flags & ETHTOOL_FLAG_COMPACT_BITSETS;
+	const struct ethtool_link_settings_hdr *lsettings;
 	int ret;
 
+	lsettings = &ksettings->base;
+
 	if (nla_put_u8(skb, ETHTOOL_A_LINKMODES_AUTONEG, lsettings->autoneg))
 		return -EMSGSIZE;
 
@@ -237,7 +241,7 @@ static int ethnl_update_linkmodes(struct genl_info *info, struct nlattr **tb,
 				  struct ethtool_link_ksettings *ksettings,
 				  bool *mod, const struct net_device *dev)
 {
-	struct ethtool_link_settings *lsettings = &ksettings->base;
+	struct ethtool_link_settings_hdr *lsettings = &ksettings->base;
 	bool req_speed, req_lanes, req_duplex;
 	const struct nlattr *master_slave_cfg, *lanes_cfg;
 	int ret;