linux-kernel - [PATCH v1 1/3] printk: honor the max_reason field in kmsg

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Date:   Sat,  2 May 2020 10:35:53 -0400
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     pasha.tatashin@...een.com, jmorris@...ei.org, sashal@...nel.org,
        linux-kernel@...r.kernel.org, pmladek@...e.com,
        sergey.senozhatsky@...il.com, rostedt@...dmis.org,
        keescook@...omium.org, anton@...msg.org, ccross@...roid.com,
        tony.luck@...el.com, robh+dt@...nel.org, devicetree@...r.kernel.org
Subject: [PATCH v1 1/3] printk: honor the max_reason field in kmsg_dumper

kmsg_dump() allows to dump kmesg buffer for various system events: oops,
panic, reboot, etc. It provides an interface to register a callback call
for clients, and in that callback interface there is a field "max_reason"
which gets ignored unless always_kmsg_dump is passed as kernel parameter.

Allow clients to decide max_reason, and keep the current behavior when
max_reason is not set.

Signed-off-by: Pavel Tatashin <pasha.tatashin@...een.com>
---
 include/linux/kmsg_dump.h |  1 +
 kernel/printk/printk.c    | 16 +++++++++-------
 2 files changed, 10 insertions(+), 7 deletions(-)

diff --git a/include/linux/kmsg_dump.h b/include/linux/kmsg_dump.h
index 2e7a1e032c71..c0d703b7ce38 100644
--- a/include/linux/kmsg_dump.h
+++ b/include/linux/kmsg_dump.h
@@ -28,6 +28,7 @@ enum kmsg_dump_reason {
 	KMSG_DUMP_RESTART,
 	KMSG_DUMP_HALT,
 	KMSG_DUMP_POWEROFF,
+	KMSG_DUMP_MAX = KMSG_DUMP_POWEROFF
 };
 
 /**
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 9a9b6156270b..04c1e9a9b139 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3085,6 +3085,8 @@ EXPORT_SYMBOL(printk_timed_ratelimit);
 
 static DEFINE_SPINLOCK(dump_list_lock);
 static LIST_HEAD(dump_list);
+static bool always_kmsg_dump;
+module_param_named(always_kmsg_dump, always_kmsg_dump, bool, S_IRUGO | S_IWUSR);
 
 /**
  * kmsg_dump_register - register a kernel log dumper.
@@ -3106,6 +3108,12 @@ int kmsg_dump_register(struct kmsg_dumper *dumper)
 	spin_lock_irqsave(&dump_list_lock, flags);
 	/* Don't allow registering multiple times */
 	if (!dumper->registered) {
+		if (!dumper->max_reason) {
+			if (always_kmsg_dump)
+				dumper->max_reason = KMSG_DUMP_MAX;
+			else
+				dumper->max_reason = KMSG_DUMP_OOPS;
+		}
 		dumper->registered = 1;
 		list_add_tail_rcu(&dumper->list, &dump_list);
 		err = 0;
@@ -3141,9 +3149,6 @@ int kmsg_dump_unregister(struct kmsg_dumper *dumper)
 }
 EXPORT_SYMBOL_GPL(kmsg_dump_unregister);
 
-static bool always_kmsg_dump;
-module_param_named(always_kmsg_dump, always_kmsg_dump, bool, S_IRUGO | S_IWUSR);
-
 /**
  * kmsg_dump - dump kernel log to kernel message dumpers.
  * @reason: the reason (oops, panic etc) for dumping
@@ -3157,12 +3162,9 @@ void kmsg_dump(enum kmsg_dump_reason reason)
 	struct kmsg_dumper *dumper;
 	unsigned long flags;
 
-	if ((reason > KMSG_DUMP_OOPS) && !always_kmsg_dump)
-		return;
-
 	rcu_read_lock();
 	list_for_each_entry_rcu(dumper, &dump_list, list) {
-		if (dumper->max_reason && reason > dumper->max_reason)
+		if (reason > dumper->max_reason)
 			continue;
 
 		/* initialize iterator with data about the stored records */
-- 
2.25.1