net: add struct kernel_hwtstamp_config and make net_hwtstamp_validate() use it

Jakub Kicinski suggested that we may want to add new UAPI for
controlling hardware timestamping through netlink in the future, and in
that case, we will be limited to the struct hwtstamp_config that is
currently passed in fixed binary format through the SIOCGHWTSTAMP and
SIOCSHWTSTAMP ioctls. It would be good if new kernel code already
started operating on an extensible kernel variant of that structure,
similar in concept to struct kernel_ethtool_coalesce vs struct
ethtool_coalesce.

Since struct hwtstamp_config is in include/uapi/linux/net_tstamp.h, here
we introduce include/linux/net_tstamp.h which shadows that other header,
but also includes it, so that existing includers of this header work as
before. In addition to that, we add the definition for the kernel-only
structure, and a helper which translates all fields by manual copying.
I am doing a manual copy in order to not force the alignment (or type)
of the fields of struct kernel_hwtstamp_config to be the same as of
struct hwtstamp_config, even though now, they are the same.

Link: https://lore.kernel.org/netdev/20230330223519.36ce7d23@kernel.org/Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/net_tstamp.h

+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _LINUX_NET_TIMESTAMPING_H_
+#define _LINUX_NET_TIMESTAMPING_H_
+
+#include <uapi/linux/net_tstamp.h>
+
+/**
+ * struct kernel_hwtstamp_config - Kernel copy of struct hwtstamp_config
+ *
+ * @flags: see struct hwtstamp_config
+ * @tx_type: see struct hwtstamp_config
+ * @rx_filter: see struct hwtstamp_config
+ *
+ * Prefer using this structure for in-kernel processing of hardware
+ * timestamping configuration, over the inextensible struct hwtstamp_config
+ * exposed to the %SIOCGHWTSTAMP and %SIOCSHWTSTAMP ioctl UAPI.
+ */
+struct kernel_hwtstamp_config {
+	int flags;
+	int tx_type;
+	int rx_filter;
+};
+
+static inline void hwtstamp_config_to_kernel(struct kernel_hwtstamp_config *kernel_cfg,
+					     const struct hwtstamp_config *cfg)
+{
+	kernel_cfg->flags = cfg->flags;
+	kernel_cfg->tx_type = cfg->tx_type;
+	kernel_cfg->rx_filter = cfg->rx_filter;
+}
+
+#endif /* _LINUX_NET_TIMESTAMPING_H_ */

net/core/dev_ioctl.c

@@ -183,7 +183,7 @@ static int dev_ifsioc_locked(struct net *net, struct ifreq *ifr, unsigned int cm
 	return err;
 }
 
-static int net_hwtstamp_validate(const struct hwtstamp_config *cfg)
+static int net_hwtstamp_validate(const struct kernel_hwtstamp_config *cfg)
 {
 	enum hwtstamp_tx_types tx_type;
 	enum hwtstamp_rx_filters rx_filter;
@@ -259,13 +259,16 @@ static int dev_get_hwtstamp(struct net_device *dev, struct ifreq *ifr)
 
 static int dev_set_hwtstamp(struct net_device *dev, struct ifreq *ifr)
 {
+	struct kernel_hwtstamp_config kernel_cfg;
 	struct hwtstamp_config cfg;
 	int err;
 
 	if (copy_from_user(&cfg, ifr->ifr_data, sizeof(cfg)))
 		return -EFAULT;
 
-	err = net_hwtstamp_validate(&cfg);
+	hwtstamp_config_to_kernel(&kernel_cfg, &cfg);
+
+	err = net_hwtstamp_validate(&kernel_cfg);
 	if (err)
 		return err;