Re: [RFC 0/8] Additional kmsg devices

On 07/03/2015 01:21 PM, Richard Weinberger wrote:

On Fri, Jul 3, 2015 at 12:49 PM, Marcin Niesluchowski
[off-list ref] wrote:

quoted

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