[PATCH v3 2/2] tty/sysrq: Dump printk ring buffer messages via sysrq

Sreenath Vijayan
2024-01-18T02:48:30Z

When terminal is unresponsive, one cannot use dmesg to view printk
ring buffer messages. Also, syslog services may be disabled,
to check the messages after a reboot, especially on embedded systems.
In this scenario, dump the printk ring buffer messages via sysrq
by pressing sysrq+D.

Signed-off-by: Sreenath Vijayan <sreenath.vijayan@sony.com>
Signed-off-by: Shimoyashiki Taichi <taichi.shimoyashiki@sony.com>
---
Documentation/admin-guide/sysrq.rst | 2 ++
drivers/tty/sysrq.c | 20 +++++++++++++++++++-
2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/sysrq.rst b/Documentation/admin-guide/sysrq.rst
index 51906e47327b..246a7b61a0eb 100644
--- a/Documentation/admin-guide/sysrq.rst
+++ b/Documentation/admin-guide/sysrq.rst
@@ -152,6 +152,8 @@ Command Function
will be printed to your console. (``0``, for example would make
it so that only emergency messages like PANICs or OOPSes would
make it to your console.)
+
+``D`` Dump the printk ring buffer
=========== ===================================================================

Okay, so what can I use them for?
diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c
index 6b4a28bcf2f5..1976412706a4 100644
--- a/drivers/tty/sysrq.c
+++ b/drivers/tty/sysrq.c
@@ -450,6 +450,24 @@ static const struct sysrq_key_op sysrq_unrt_op = {
.enable_mask = SYSRQ_ENABLE_RTNICE,
};

+static void dmesg_dump_callback(struct work_struct *work)
+{
+ dump_printk_buffer();
+}
+
+static DECLARE_WORK(sysrq_dmesg_work, dmesg_dump_callback);
+
+static void sysrq_handle_dmesg_dump(u8 key)
+{
+ queue_work(system_unbound_wq, &sysrq_dmesg_work);
+}
+static struct sysrq_key_op sysrq_dmesg_dump_op = {
+ .handler = sysrq_handle_dmesg_dump,
+ .help_msg = "dump-dmesg(D)",
+ .action_msg = "Dump dmesg",
+ .enable_mask = SYSRQ_ENABLE_DUMP,
+};
+
/* Key Operations table and lock */
static DEFINE_SPINLOCK(sysrq_key_table_lock);

@@ -505,7 +523,7 @@ static const struct sysrq_key_op *sysrq_key_table[62] = {
NULL, /* A */
NULL, /* B */
NULL, /* C */
- NULL, /* D */
+ &sysrq_dmesg_dump_op, /* D */
NULL, /* E */
NULL, /* F */
NULL, /* G */
--
2.43.0