User code can now set the log area and severity of log messages. This also updates the j6_log
syscall to take these parameters, but removes all calls to it except through j6::syslog().
This commit does a number of things to start the transition of channels
from kernel to user space:
- Remove channel objects / syscalls from the kernel
- Add mutex type in libj6
- Add condition type in libj6
- Add a `ring` type flag for VMA syscalls to create ring buffers
- Implement a rudimentary shared memory channel using all of the above