[PATCH net-next 2/4] netconsole: Add configfs attribute for direct message sending

[Breno Leitao <leitao@debian.org>]

Add a new write-only configfs attribute "send_msg" to netconsole targets
that allows sending arbitrary messages directly through netconsole.

This feature enables users to send custom messages through netconsole
without having to go through the kernel logging infrastructure. Messages
can be sent by simply writing to:
/sys/kernel/config/netconsole/<target>/send_msg

The implementation:
- Checks if the target is enabled before sending
- Verifies the network interface is running
- Handles both basic and extended message formats
- Fragments large messages when needed for basic targets
- Reuses existing send_msg_udp() and send_ext_msg_udp() functions

Unfortunately this patch has two forward declaration, which is not
ideal, but, moving send_msg_udp() functions earlier would cause too many
changes, and this could be done in an idependent patch.

Signed-off-by: Breno Leitao <leitao@debian.org>
---
 drivers/net/netconsole.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index dc3bd7c9b049..245ed2584bbb 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -1194,6 +1194,39 @@ static const struct config_item_type userdata_type = {
 	.ct_owner	= THIS_MODULE,
 };
 
+/* Forward declarations */
+static void send_ext_msg_udp(struct netconsole_target *nt, const char *msg,
+			     int msg_len);
+static void send_msg_udp(struct netconsole_target *nt, const char *msg,
+			 unsigned int len);
+
+static ssize_t send_msg_store(struct config_item *item, const char *buf,
+			      size_t count)
+{
+	struct netconsole_target *nt = to_target(item);
+	ssize_t ret = -EINVAL;
+	unsigned long flags;
+
+	mutex_lock(&dynamic_netconsole_mutex);
+	if (!nt->enabled)
+		goto out;
+
+	if (!netif_running(nt->np.dev))
+		goto out;
+
+	spin_lock_irqsave(&target_list_lock, flags);
+	if (nt->extended)
+		send_ext_msg_udp(nt, buf, count);
+	else
+		send_msg_udp(nt, buf, count);
+	spin_unlock_irqrestore(&target_list_lock, flags);
+
+	ret = count;
+out:
+	mutex_unlock(&dynamic_netconsole_mutex);
+
+	return ret;
+}
 CONFIGFS_ATTR(, enabled);
 CONFIGFS_ATTR(, extended);
 CONFIGFS_ATTR(, dev_name);
@@ -1205,6 +1238,7 @@ CONFIGFS_ATTR_RO(, local_mac);
 CONFIGFS_ATTR(, remote_mac);
 CONFIGFS_ATTR(, release);
 CONFIGFS_ATTR_RO(, transmit_errors);
+CONFIGFS_ATTR_WO(, send_msg);
 
 static struct configfs_attribute *netconsole_target_attrs[] = {
 	&attr_enabled,
@@ -1218,6 +1252,7 @@ static struct configfs_attribute *netconsole_target_attrs[] = {
 	&attr_local_mac,
 	&attr_remote_mac,
 	&attr_transmit_errors,
+	&attr_send_msg,
 	NULL,
 };
 

-- 
2.47.3