[ros-dev] Advice required on User-mode to Kernel mode call for syslog(2) analog in ROS

[Minas Abrahamyan]

Hi all,

I'm going to implement dmesg.exe, a ROS application to read dmesg/kmsg
buffer (debug messages in kernel buffer),
which is filled in by appropriate patch 6018
(here: http://www.reactos.org/bugzilla/show_bug.cgi?id=6018 ) (BTW,
it's not yet reviewed and not applied!).

So I'm requesting advice on:
What would be the better way for user-mode code to get the contents of
kmsg buffer in kernel-space (kdbg)?

Shortly:
Linux has special system call "syslog" (man 2 syslog)
FreeBSD uses its special sysctl interface to kernel along with
'kern.msgbuf' parameter.

My questions:
Do we need special system call like Linux, or even more, the whole
family of them (sysctl('*')) as in BSD?
How to implement simple system call for it, now?

---
Now detailed info for unices:

Linux case:
* syslog(2) - read and/or clear kernel message ring buffer; set console_loglevel
int syslog(int type, char *bufp, int len);

* also /proc/kmsg virtual file, which when being read returns buffer contents
==excerpt from man proc ==
/proc/kmsg
              This file can be used instead of the syslog(2)  system
call  to  read  kernel  messages.   A
              process  must  have  superuser privileges to read this
file, and only one process should read
              this file.  This file should not be read if a syslog
process is running which uses  the  sys‐
              log(2) system call facility to log kernel messages.

              Information in this file is retrieved with the dmesg(1) program.
==eo exerpt==

dmesg in FreeBSD:
Parameter 'kern.msgbuf' given to sysctl(3)  returns contents of kernel
message buffer.
There is also 'kern.msgbuf_clear' to clean the buffer.
---

WBR,
Minas Abrahamyan