[PATCH v2] netconsole: Append kernel version to message

[Breno Leitao <leitao@debian.org>]

Create a new netconsole runtime option that prepends the kernel version in
the netconsole message. This is useful to map kernel messages to kernel
version in a simple way, i.e., without checking somewhere which kernel
version the host that sent the message is using.

If this option is selected, then the "<release>," is prepended before the
netconsole message. This is an example of a netconsole output, with
release feature enabled:

	6.4.0-01762-ga1ba2ffe946e;12,426,112883998,-;this is a test

Calvin Owens send a RFC about this problem in 2016[1], but his
approach was a bit more intrusive, changing the printk subsystem. This
approach is lighter, and just append the information in the last mile,
just before netconsole push the message to netpoll.

[1] Link: https://lore.kernel.org/all/51047c0f6e86abcb9ee13f60653b6946f8fcfc99.1463172791.git.calvinowens@fb.com/

Cc: Dave Jones <davej@codemonkey.org.uk>
Signed-off-by: Breno Leitao <leitao@debian.org>
---
V1 -> V2:
 * Configured at runtime instead of at compilation time
 * Reuse send_ext_msg_udp to avoid extra memory allocation
---

 Documentation/networking/netconsole.rst | 11 +++-
 drivers/net/netconsole.c                | 80 ++++++++++++++++++++++++-
 2 files changed, 87 insertions(+), 4 deletions(-)

diff --git a/Documentation/networking/netconsole.rst b/Documentation/networking/netconsole.rst
index dd0518e002f6..7a9de0568e84 100644
--- a/Documentation/networking/netconsole.rst
+++ b/Documentation/networking/netconsole.rst
@@ -13,6 +13,8 @@ IPv6 support by Cong Wang <xiyou.wangcong@gmail.com>, Jan 1 2013
 
 Extended console support by Tejun Heo <tj@kernel.org>, May 1 2015
 
+Release prepend support by Breno Leitao <leitao@debian.org>, Jul 7 2023
+
 Please send bug reports to Matt Mackall <mpm@selenic.com>
 Satyam Sharma <satyam.sharma@gmail.com>, and Cong Wang <xiyou.wangcong@gmail.com>
 
@@ -34,10 +36,11 @@ Sender and receiver configuration:
 It takes a string configuration parameter "netconsole" in the
 following format::
 
- netconsole=[+][src-port]@[src-ip]/[<dev>],[tgt-port]@<tgt-ip>/[tgt-macaddr]
+ netconsole=[+][r][src-port]@[src-ip]/[<dev>],[tgt-port]@<tgt-ip>/[tgt-macaddr]
 
    where
 	+             if present, enable extended console support
+	r             if present, prepend kernel version (release) to the message
 	src-port      source for UDP packets (defaults to 6665)
 	src-ip        source IP to use (interface address)
 	dev           network interface (eth0)
@@ -125,6 +128,7 @@ The interface exposes these parameters of a netconsole target to userspace:
 	==============  =================================       ============
 	enabled		Is this target currently enabled?	(read-write)
 	extended	Extended mode enabled			(read-write)
+	release		Prepend kernel release to message	(read-write)
 	dev_name	Local network interface name		(read-write)
 	local_port	Source UDP port to use			(read-write)
 	remote_port	Remote agent's UDP port			(read-write)
@@ -165,6 +169,11 @@ following format which is the same as /dev/kmsg::
 
  <level>,<sequnum>,<timestamp>,<contflag>;<message text>
 
+If 'r' (release) feature is enabled, the kernel release version is
+prepended to the start of the message. Example::
+
+ 6.4.0,6,444,501151268,-;netconsole: network logging started
+
 Non printable characters in <message text> are escaped using "\xff"
 notation. If the message contains optional dictionary, verbatim
 newline is used as the delimiter.
diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index 4f4f79532c6c..a72f471ddf02 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -36,6 +36,7 @@
 #include <linux/inet.h>
 #include <linux/configfs.h>
 #include <linux/etherdevice.h>
+#include <linux/utsname.h>
 
 MODULE_AUTHOR("Maintainer: Matt Mackall <mpm@selenic.com>");
 MODULE_DESCRIPTION("Console driver for network interfaces");
@@ -84,6 +85,8 @@ static struct console netconsole_ext;
  *		Also, other parameters of a target may be modified at
  *		runtime only when it is disabled (enabled == 0).
  * @extended:	Denotes whether console is extended or not.
+ * @release:	Denotes whether kernel release version should be prepended
+ *		to the message. Depends on extended console.
  * @np:		The netpoll structure for this target.
  *		Contains the other userspace visible parameters:
  *		dev_name	(read-write)
@@ -101,6 +104,7 @@ struct netconsole_target {
 #endif
 	bool			enabled;
 	bool			extended;
+	bool			release;
 	struct netpoll		np;
 };
 
@@ -188,6 +192,14 @@ static struct netconsole_target *alloc_param_target(char *target_config)
 		target_config++;
 	}
 
+	if (*target_config == 'r') {
+		if (!nt->extended)
+			pr_err("Not enabling release feature, since extended message is disabled\n");
+		else
+			nt->release = true;
+		target_config++;
+	}
+
 	/* Parse parameters and setup netpoll */
 	err = netpoll_parse_options(&nt->np, target_config);
 	if (err)
@@ -222,6 +234,7 @@ static void free_param_target(struct netconsole_target *nt)
  *				|
  *				<target>/
  *				|	enabled
+ *				|	release
  *				|	dev_name
  *				|	local_port
  *				|	remote_port
@@ -254,6 +267,11 @@ static ssize_t extended_show(struct config_item *item, char *buf)
 	return snprintf(buf, PAGE_SIZE, "%d\n", to_target(item)->extended);
 }
 
+static ssize_t release_show(struct config_item *item, char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "%d\n", to_target(item)->release);
+}
+
 static ssize_t dev_name_show(struct config_item *item, char *buf)
 {
 	return snprintf(buf, PAGE_SIZE, "%s\n", to_target(item)->np.dev_name);
@@ -332,6 +350,11 @@ static ssize_t enabled_store(struct config_item *item,
 	}
 
 	if (enabled) {	/* true */
+		if (nt->release && !nt->extended) {
+			pr_err("release feature requires extended log message\n");
+			goto out_unlock;
+		}
+
 		if (nt->extended && !console_is_registered(&netconsole_ext))
 			register_console(&netconsole_ext);
 
@@ -366,6 +389,38 @@ static ssize_t enabled_store(struct config_item *item,
 	return err;
 }
 
+static ssize_t release_store(struct config_item *item, const char *buf,
+			     size_t count)
+{
+	struct netconsole_target *nt = to_target(item);
+	int release;
+	int err;
+
+	mutex_lock(&dynamic_netconsole_mutex);
+	if (nt->enabled) {
+		pr_err("target (%s) is enabled, disable to update parameters\n",
+		       config_item_name(&nt->item));
+		err = -EINVAL;
+		goto out_unlock;
+	}
+
+	err = kstrtoint(buf, 10, &release);
+	if (err < 0)
+		goto out_unlock;
+	if (release < 0 || release > 1) {
+		err = -EINVAL;
+		goto out_unlock;
+	}
+
+	nt->release = release;
+
+	mutex_unlock(&dynamic_netconsole_mutex);
+	return strnlen(buf, count);
+out_unlock:
+	mutex_unlock(&dynamic_netconsole_mutex);
+	return err;
+}
+
 static ssize_t extended_store(struct config_item *item, const char *buf,
 		size_t count)
 {
@@ -576,10 +631,12 @@ CONFIGFS_ATTR(, local_ip);
 CONFIGFS_ATTR(, remote_ip);
 CONFIGFS_ATTR_RO(, local_mac);
 CONFIGFS_ATTR(, remote_mac);
+CONFIGFS_ATTR(, release);
 
 static struct configfs_attribute *netconsole_target_attrs[] = {
 	&attr_enabled,
 	&attr_extended,
+	&attr_release,
 	&attr_dev_name,
 	&attr_local_port,
 	&attr_remote_port,
@@ -772,9 +829,23 @@ static void send_ext_msg_udp(struct netconsole_target *nt, const char *msg,
 	const char *header, *body;
 	int offset = 0;
 	int header_len, body_len;
+	const char *msg_ready = msg;
+	const char *release;
+	int release_len = 0;
+
+	if (nt->release) {
+		release = init_utsname()->release;
+		release_len = strlen(release) + 1;
+	}
 
-	if (msg_len <= MAX_PRINT_CHUNK) {
-		netpoll_send_udp(&nt->np, msg, msg_len);
+	if (msg_len + release_len <= MAX_PRINT_CHUNK) {
+		/* No fragmentation needed */
+		if (nt->release) {
+			scnprintf(buf, MAX_PRINT_CHUNK, "%s,%s", release, msg);
+			msg_len += release_len;
+			msg_ready = buf;
+		}
+		netpoll_send_udp(&nt->np, msg_ready, msg_len);
 		return;
 	}
 
@@ -792,7 +863,10 @@ static void send_ext_msg_udp(struct netconsole_target *nt, const char *msg,
 	 * Transfer multiple chunks with the following extra header.
 	 * "ncfrag=<byte-offset>/<total-bytes>"
 	 */
-	memcpy(buf, header, header_len);
+	if (nt->release)
+		scnprintf(buf, MAX_PRINT_CHUNK, "%s,", release);
+	memcpy(buf + release_len, header, header_len);
+	header_len += release_len;
 
 	while (offset < body_len) {
 		int this_header = header_len;
-- 
2.34.1