# Re: \[RFC 0/8\] Additional kmsg devices

- From: Marcin Niesluchowski \<hidden\>
- Date: 2015-07-03 15:09:16 
- List: linux-api
- Page: https://ratatoskr.run/linux-api/2015/07/4527202
- Thread: https://ratatoskr.run/linux-api/2015/07/4527040/t.md

```text
On 07/03/2015 01:21 PM, Richard Weinberger wrote:
> On Fri, Jul 3, 2015 at 12:49 PM, Marcin Niesluchowski
> [ref] wrote:
>> Dear All,
>>
>> This series of patches extends kmsg interface with ability to dynamicaly
>> create (and destroy) kmsg-like devices which can be used by user space
>> for logging. Logging to kernel has number of benefits, including but not
>> limited to - always available, requiring no userspace, automatically
>> rotating and low overhead.
>>
>> User-space logging to kernel cyclic buffers was already successfully used
>> in android logger concept but it had certain flaws that this commits try
>> to address:
>> * drops hardcoded number of devices and static paths in favor for dynamic
>>    configuration by ioctl interface in userspace
>> * extends existing driver instead of creating completely new one
> So, now we start moving syslogd into kernel land because userspace is
> too broken to provide
> decent logging?
>
> I can understand the systemd is using kmsg if no other logging service
> is available
> but I really don't think we should encourage other programs to do so.
>
> Why can't you just make sure that your target has a working
> syslogd/rsyslogd/journald/whatever?
> All can be done perfectly fine in userspace.
* Message credibility: Lets imagine simple service which collects logs via unix sockets. There is no reliable way of identifying logging process. getsockopt() with SO_PEERCRED option would give pid form cred structure, but according to manual it may not be of actual logging process:
  "The returned credentials are those that were in effect at the time of the call to connect(2) or socketpair(2)."
      - select(7)

* Early userspace tool: Helpful especially for embeded systems.

* Reliability: Userspace service may be killed due to out of memory (OOM). This is kernel cyclic buffer, which size can be specified differently according to situation.

* Possibility of using it with pstore: This code could be extended to log additional buffers to persistent storage same way main (kmsg) log buffer is.

* Use case of attaching file descriptor to stdout/stderr: Especially in early userspace.

* Performance: Those services mentioned by You are weeker solutions in that case. Especially systemd-journald is much too heavy soulution.

-- 

Best Regards,
Marcin Niesluchowski
```