On 07/03/2015 01:21 PM, Richard Weinberger wrote:
On Fri, Jul 3, 2015 at 12:49 PM, Marcin Niesluchowski
<m.niesluchow@xxxxxxxxxxx> 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
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