[PATCH net-next v2 0/5] netconsole: Add support for msgid in sysdata

[PATCH net-next v2 0/5] netconsole: Add support for msgid in sysdata

[Gustavo Luiz Duarte]

This patch series introduces a new feature to netconsole which allows
appending a message ID to the userdata dictionary.

If the msgid feature is enabled, the message ID is built from a per-target 32
bit counter that is incremented and appended to every message sent to the target.

Example::
  echo 1 > "/sys/kernel/config/netconsole/cmdline0/userdata/msgid_enabled"
  echo "This is message #1" > /dev/kmsg
  echo "This is message #2" > /dev/kmsg
  13,434,54928466,-;This is message #1
   msgid=1
  13,435,54934019,-;This is message #2
   msgid=2

This feature can be used by the target to detect if messages were dropped or
reordered before reaching the target. This allows system administrators to
assess the reliability of their netconsole pipeline and detect loss of messages
due to network contention or temporary unavailability.

Suggested-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Gustavo Luiz Duarte <gustavold@gmail.com>

---
Changes in v2:
- Use wrapping_assign_add() to avoid warnings in UBSAN and friends.
- Improve documentation to clarify wrapping and distinguish msgid from sequnum.
- Rebase and fix conflict in prepare_extradata().
- Link to v1: https://lore.kernel.org/r/20250611-netconsole-msgid-v1-0-1784a51feb1e@gmail.com

---
Gustavo Luiz Duarte (5):
      netconsole: introduce 'msgid' as a new sysdata field
      netconsole: implement configfs for msgid_enabled
      netconsole: append msgid to sysdata
      selftests: netconsole: Add tests for 'msgid' feature in sysdata
      docs: netconsole: document msgid feature

 Documentation/networking/netconsole.rst            | 32 +++++++++++
 drivers/net/netconsole.c                           | 65 ++++++++++++++++++++++
 .../selftests/drivers/net/netcons_sysdata.sh       | 30 ++++++++++
 3 files changed, 127 insertions(+)
---
base-commit: 535de528015b56e34a40a8e1eb1629fadf809a84
change-id: 20250609-netconsole-msgid-b93c6f8e9c60

Best regards,
-- 
Gustavo Luiz Duarte <gustavold@gmail.com>

[PATCH net-next v2 1/5] netconsole: introduce 'msgid' as a new sysdata field

[Gustavo Luiz Duarte]

This adds a new sysdata field to enable assigning a per-target unique id
to each message sent to that target. This id can later be appended as
part of sysdata, allowing targets to detect dropped netconsole messages.
Update count_extradata_entries() to take the new field into account.

Reviewed-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Gustavo Luiz Duarte <gustavold@gmail.com>
---
 drivers/net/netconsole.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index 1eb678e07dd0..5f8c8c6c5393 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -113,6 +113,8 @@ enum sysdata_feature {
 	SYSDATA_TASKNAME = BIT(1),
 	/* Kernel release/version as part of sysdata */
 	SYSDATA_RELEASE = BIT(2),
+	/* Include a per-target message ID as part of sysdata */
+	SYSDATA_MSGID = BIT(3),
 };
 
 /**
@@ -782,6 +784,8 @@ static size_t count_extradata_entries(struct netconsole_target *nt)
 		entries += 1;
 	if (nt->sysdata_fields & SYSDATA_RELEASE)
 		entries += 1;
+	if (nt->sysdata_fields & SYSDATA_MSGID)
+		entries += 1;
 
 	return entries;
 }

-- 
2.47.1

[PATCH net-next v2 2/5] netconsole: implement configfs for msgid_enabled

[Gustavo Luiz Duarte]

Implement the _show and _store functions for the msgid_enabled configfs
attribute under userdata.
Set the sysdata_fields bit accordingly.

Reviewed-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Gustavo Luiz Duarte <gustavold@gmail.com>
---
 drivers/net/netconsole.c | 49 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index 5f8c8c6c5393..3bf8777fcd01 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -489,6 +489,19 @@ static void unregister_netcons_consoles(void)
 		unregister_console(&netconsole);
 }
 
+static ssize_t sysdata_msgid_enabled_show(struct config_item *item,
+					  char *buf)
+{
+	struct netconsole_target *nt = to_target(item->ci_parent);
+	bool msgid_enabled;
+
+	mutex_lock(&dynamic_netconsole_mutex);
+	msgid_enabled = !!(nt->sysdata_fields & SYSDATA_MSGID);
+	mutex_unlock(&dynamic_netconsole_mutex);
+
+	return sysfs_emit(buf, "%d\n", msgid_enabled);
+}
+
 /*
  * This one is special -- targets created through the configfs interface
  * are not enabled (and the corresponding netpoll activated) by default.
@@ -922,6 +935,40 @@ static void disable_sysdata_feature(struct netconsole_target *nt,
 	nt->extradata_complete[nt->userdata_length] = 0;
 }
 
+static ssize_t sysdata_msgid_enabled_store(struct config_item *item,
+					   const char *buf, size_t count)
+{
+	struct netconsole_target *nt = to_target(item->ci_parent);
+	bool msgid_enabled, curr;
+	ssize_t ret;
+
+	ret = kstrtobool(buf, &msgid_enabled);
+	if (ret)
+		return ret;
+
+	mutex_lock(&dynamic_netconsole_mutex);
+	curr = !!(nt->sysdata_fields & SYSDATA_MSGID);
+	if (msgid_enabled == curr)
+		goto unlock_ok;
+
+	if (msgid_enabled &&
+	    count_extradata_entries(nt) >= MAX_EXTRADATA_ITEMS) {
+		ret = -ENOSPC;
+		goto unlock;
+	}
+
+	if (msgid_enabled)
+		nt->sysdata_fields |= SYSDATA_MSGID;
+	else
+		disable_sysdata_feature(nt, SYSDATA_MSGID);
+
+unlock_ok:
+	ret = strnlen(buf, count);
+unlock:
+	mutex_unlock(&dynamic_netconsole_mutex);
+	return ret;
+}
+
 static ssize_t sysdata_release_enabled_store(struct config_item *item,
 					     const char *buf, size_t count)
 {
@@ -1037,6 +1084,7 @@ CONFIGFS_ATTR(userdatum_, value);
 CONFIGFS_ATTR(sysdata_, cpu_nr_enabled);
 CONFIGFS_ATTR(sysdata_, taskname_enabled);
 CONFIGFS_ATTR(sysdata_, release_enabled);
+CONFIGFS_ATTR(sysdata_, msgid_enabled);
 
 static struct configfs_attribute *userdatum_attrs[] = {
 	&userdatum_attr_value,
@@ -1099,6 +1147,7 @@ static struct configfs_attribute *userdata_attrs[] = {
 	&sysdata_attr_cpu_nr_enabled,
 	&sysdata_attr_taskname_enabled,
 	&sysdata_attr_release_enabled,
+	&sysdata_attr_msgid_enabled,
 	NULL,
 };
 

-- 
2.47.1

[PATCH net-next v2 3/5] netconsole: append msgid to sysdata

[Gustavo Luiz Duarte]

Add msgcounter to the netconsole_target struct to generate message IDs.
If the msgid_enabled attribute is true, increment msgcounter and append
msgid=<msgcounter> to sysdata buffer before sending the message.

Signed-off-by: Gustavo Luiz Duarte <gustavold@gmail.com>
---
 drivers/net/netconsole.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
index 3bf8777fcd01..baa9862c1bc3 100644
--- a/drivers/net/netconsole.c
+++ b/drivers/net/netconsole.c
@@ -155,6 +155,8 @@ struct netconsole_target {
 	size_t			userdata_length;
 	/* bit-wise with sysdata_feature bits */
 	u32			sysdata_fields;
+	/* protected by target_list_lock */
+	u32			msgcounter;
 #endif
 	struct netconsole_target_stats stats;
 	bool			enabled;
@@ -1345,6 +1347,14 @@ static int sysdata_append_release(struct netconsole_target *nt, int offset)
 			 init_utsname()->release);
 }
 
+static int sysdata_append_msgid(struct netconsole_target *nt, int offset)
+{
+	wrapping_assign_add(nt->msgcounter, 1);
+	return scnprintf(&nt->extradata_complete[offset],
+			 MAX_EXTRADATA_ENTRY_LEN, " msgid=%u\n",
+			 nt->msgcounter);
+}
+
 /*
  * prepare_extradata - append sysdata at extradata_complete in runtime
  * @nt: target to send message to
@@ -1367,6 +1377,8 @@ static int prepare_extradata(struct netconsole_target *nt)
 		extradata_len += sysdata_append_taskname(nt, extradata_len);
 	if (nt->sysdata_fields & SYSDATA_RELEASE)
 		extradata_len += sysdata_append_release(nt, extradata_len);
+	if (nt->sysdata_fields & SYSDATA_MSGID)
+		extradata_len += sysdata_append_msgid(nt, extradata_len);
 
 	WARN_ON_ONCE(extradata_len >
 		     MAX_EXTRADATA_ENTRY_LEN * MAX_EXTRADATA_ITEMS);

-- 
2.47.1

[PATCH net-next v2 4/5] selftests: netconsole: Add tests for 'msgid' feature in sysdata

[Gustavo Luiz Duarte]

Extend the self-tests to cover the 'msgid' feature in sysdata.

Verify that msgid is appended to the message when the feature is enabled
and that it is not appended when the feature is disabled.

Signed-off-by: Gustavo Luiz Duarte <gustavold@gmail.com>
---
 .../selftests/drivers/net/netcons_sysdata.sh       | 30 ++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/tools/testing/selftests/drivers/net/netcons_sysdata.sh b/tools/testing/selftests/drivers/net/netcons_sysdata.sh
index a737e377bf08..baf69031089e 100755
--- a/tools/testing/selftests/drivers/net/netcons_sysdata.sh
+++ b/tools/testing/selftests/drivers/net/netcons_sysdata.sh
@@ -53,6 +53,17 @@ function set_release() {
 	echo 1 > "${NETCONS_PATH}/userdata/release_enabled"
 }
 
+# Enable the msgid to be appended to sysdata
+function set_msgid() {
+	if [[ ! -f "${NETCONS_PATH}/userdata/msgid_enabled" ]]
+	then
+		echo "Not able to enable msgid sysdata append. Configfs not available in ${NETCONS_PATH}/userdata/msgid_enabled" >&2
+		exit "${ksft_skip}"
+	fi
+
+	echo 1 > "${NETCONS_PATH}/userdata/msgid_enabled"
+}
+
 # Disable the sysdata cpu_nr feature
 function unset_cpu_nr() {
 	echo 0 > "${NETCONS_PATH}/userdata/cpu_nr_enabled"
@@ -67,6 +78,10 @@ function unset_release() {
 	echo 0 > "${NETCONS_PATH}/userdata/release_enabled"
 }
 
+function unset_msgid() {
+	echo 0 > "${NETCONS_PATH}/userdata/msgid_enabled"
+}
+
 # Test if MSG contains sysdata
 function validate_sysdata() {
 	# OUTPUT_FILE will contain something like:
@@ -74,6 +89,7 @@ function validate_sysdata() {
 	#  userdatakey=userdatavalue
 	#  cpu=X
 	#  taskname=<taskname>
+	#  msgid=<id>
 
 	# Echo is what this test uses to create the message. See runtest()
 	# function
@@ -104,6 +120,12 @@ function validate_sysdata() {
 		exit "${ksft_fail}"
 	fi
 
+	if ! grep -q "msgid=[0-9]\+$" "${OUTPUT_FILE}"; then
+		echo "FAIL: 'msgid=<id>' not found in ${OUTPUT_FILE}" >&2
+		cat "${OUTPUT_FILE}" >&2
+		exit "${ksft_fail}"
+	fi
+
 	rm "${OUTPUT_FILE}"
 	pkill_socat
 }
@@ -155,6 +177,12 @@ function validate_no_sysdata() {
 		exit "${ksft_fail}"
 	fi
 
+	if grep -q "msgid=" "${OUTPUT_FILE}"; then
+		echo "FAIL: 'msgid=  found in ${OUTPUT_FILE}" >&2
+		cat "${OUTPUT_FILE}" >&2
+		exit "${ksft_fail}"
+	fi
+
 	rm "${OUTPUT_FILE}"
 }
 
@@ -206,6 +234,7 @@ set_cpu_nr
 # Enable taskname to be appended to sysdata
 set_taskname
 set_release
+set_msgid
 runtest
 # Make sure the message was received in the dst part
 # and exit
@@ -235,6 +264,7 @@ MSG="Test #3 from CPU${CPU}"
 unset_cpu_nr
 unset_taskname
 unset_release
+unset_msgid
 runtest
 # At this time, cpu= shouldn't be present in the msg
 validate_no_sysdata

-- 
2.47.1

[PATCH net-next v2 5/5] docs: netconsole: document msgid feature

[Gustavo Luiz Duarte]

Add documentation explaining the msgid feature in netconsole.

This feature appends unique id to the userdata dictionary. The message
ID is populated from a per-target 32 bit counter which is incremented
for each message sent to the target. This allows a target to detect if
messages are dropped before reaching the target.

Signed-off-by: Gustavo Luiz Duarte <gustavold@gmail.com>
---
 Documentation/networking/netconsole.rst | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/Documentation/networking/netconsole.rst b/Documentation/networking/netconsole.rst
index a0076b542e9c..59cb9982afe6 100644
--- a/Documentation/networking/netconsole.rst
+++ b/Documentation/networking/netconsole.rst
@@ -340,6 +340,38 @@ In this example, the message was sent by CPU 42.
       cpu=42    # kernel-populated value
 
 
+Message ID auto population in userdata
+--------------------------------------
+
+Within the netconsole configfs hierarchy, there is a file named `msgid_enabled`
+located in the `userdata` directory. This file controls the message ID
+auto-population feature, which assigns a numeric id to each message sent to a
+given target and appends the ID to userdata dictionary in every message sent.
+
+The message ID is generated using a per-target 32 bit counter that is
+incremented for every message sent to the target. Note that this counter will
+eventually wrap around after reaching uint32_t max value, so the message ID is
+not globally unique over time. However, it can still be used by the target to
+detect if messages were dropped before reaching the target by identifying gaps
+in the sequence of IDs.
+
+It is important to distinguish message IDs from the message <sequnum> field.
+Some kernel messages may never reach netconsole (for example, due to printk
+rate limiting). Thus, a gap in <sequnum> cannot be solely relied upon to
+indicate that a message was dropped during transmission, as it may never have
+been sent via netconsole. The message ID, on the other hand, is only assigned
+to messages that are actually transmitted via netconsole.
+
+Example::
+
+  echo "This is message #1" > /dev/kmsg
+  echo "This is message #2" > /dev/kmsg
+  13,434,54928466,-;This is message #1
+   msgid=1
+  13,435,54934019,-;This is message #2
+   msgid=2
+
+
 Extended console:
 =================
 

-- 
2.47.1

Re: [PATCH net-next v2 5/5] docs: netconsole: document msgid feature

[Bagas Sanjaya]

[-- Attachment #1: Type: text/plain, Size: 537 bytes --]

On Thu, Jun 12, 2025 at 01:02:18PM -0700, Gustavo Luiz Duarte wrote:
> +Within the netconsole configfs hierarchy, there is a file named `msgid_enabled`
> +located in the `userdata` directory. This file controls the message ID
> +auto-population feature, which assigns a numeric id to each message sent to a
> +given target and appends the ID to userdata dictionary in every message sent.

/sys/kernel/config/netconsole/cmdline0/userdata/msgid_enabled?

Confused... 

-- 
An old man doll... just what I always wanted! - Clara

[-- Attachment #2: signature.asc --]
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Re: [PATCH net-next v2 3/5] netconsole: append msgid to sysdata

[Jakub Kicinski]

On Thu, 12 Jun 2025 13:02:16 -0700 Gustavo Luiz Duarte wrote:
> diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
> index 3bf8777fcd01..baa9862c1bc3 100644
> --- a/drivers/net/netconsole.c
> +++ b/drivers/net/netconsole.c
> @@ -155,6 +155,8 @@ struct netconsole_target {
>  	size_t			userdata_length;
>  	/* bit-wise with sysdata_feature bits */
>  	u32			sysdata_fields;
> +	/* protected by target_list_lock */
> +	u32			msgcounter;
>  #endif

kdoc is complaining that:

drivers/net/netconsole.c:167 struct member 'msgcounter' not described in 'netconsole_target'
-- 
pw-bot: cr

Re: [PATCH net-next v2 3/5] netconsole: append msgid to sysdata

[Gustavo Luiz Duarte]

On Sat, Jun 14, 2025 at 8:51 PM Jakub Kicinski <kuba@kernel.org> wrote:
>
> On Thu, 12 Jun 2025 13:02:16 -0700 Gustavo Luiz Duarte wrote:
> > diff --git a/drivers/net/netconsole.c b/drivers/net/netconsole.c
> > index 3bf8777fcd01..baa9862c1bc3 100644
> > --- a/drivers/net/netconsole.c
> > +++ b/drivers/net/netconsole.c
> > @@ -155,6 +155,8 @@ struct netconsole_target {
> >       size_t                  userdata_length;
> >       /* bit-wise with sysdata_feature bits */
> >       u32                     sysdata_fields;
> > +     /* protected by target_list_lock */
> > +     u32                     msgcounter;
> >  #endif
>
> kdoc is complaining that:
>
> drivers/net/netconsole.c:167 struct member 'msgcounter' not described in 'netconsole_target'

Good catch. I'm sending v3 to fix this (will also add kdoc check to my
pre-send checklist).
Thanks for the review!