On Sat, 2 May 2020 10:35:53 -0400
Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> wrote:
> 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@xxxxxxxxxx>
> ---
> 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
Hmm, I didn't realize that enums were allowed to have duplicates. That can
usually screw up logic. I would recommend making that a define afterward.
#define KMSG_DUMP_MAX KMSG_DUMP_POWEROFF
As is done in other locations of the kernel.
The rest looks fine to me.
-- Steve
> };
>
> /**
> 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 */
