logger sample fails on qemu_xtensa due to lack of backend

[nashif]

Getting no output on both, see PR #10163 and the CI results.

[nordic-krch]

@finikorg @aescolar question: you've been involved in adding native_posix backend to the logger. Have you tried to run logger example on native_posix? I don't see any output.

@nashif regarding qemu_xtensa target. It has no logger backends (as uart is the only available).

[aescolar]

Regarding the native_posix case:
it was working on: 8644203
it was broken on: 68249ce
(after merging #9362)

Bisecting:
ok - c71a559
nok - ba01a39

[aescolar]

Which is not really surprissing:

------------------------ subsys/logging/CMakeLists.txt ------------------------
index a27cf1e..e46c5e0 100644
@@ -15,6 +15,6 @@ zephyr_sources_ifdef(
   )
 
 zephyr_sources_ifdef(
-  CONFIG_LOG_BACKEND_NATIVE_POSIX
-  log_backend_native_posix.c
+  CONFIG_LOG_CMDS
+  log_cmds.c
   )

[aescolar]

I'll make a PR to fix that merge screw up.

[nashif]

@nashif regarding qemu_xtensa target. It has no logger backends (as uart is the only available).

I am not sure I am following this, why does it need a special logger backend? it was logging just fine with old logger to the console. How is this different from qemu_x86 or qemu_nios2? What logger backends do those have?

[finikorg]

qemu uses own UART so it uses usual UART logging backend, @nordic-krch native_posix backend in only for native_posix board configuration.

[nordic-krch]

@nashif

I am not sure I am following this, why does it need a special logger backend? it was logging just fine with old logger to the console.

It's because new logger does not have (yet?) console backend. It has uart backend. So if target has no uart (or native_posix, or rtt when pr comes) it cannot do logging. We should add console backend but we need to be aware that it is byte API so it will slower than optimized uart backend (current uart backend is polling based, it's poor and needs to be improved as well but at least there is room for improvement).

[finikorg]

native_posix should be working fine, I tested several samples, all OK.