samples/net/sockets/socketpair does not run as expected

[rymaj]

Describe the bug
I tried to run samples/net/socket/socketpair, and got the folllowing issue first,

*** Booting Zephyr OS build zephyr-v3.2.0-585-ge80a0c35e666  ***
Alpha: socketpair: 1 <=> 0
Bravo: socketpair: 3 <=> 2
socketpair failed: 23
Alpha closed fd 0
Bravo closed fd 2

Then I figure out I need to increase the default CONFIG_POSIX_MAX_FDS from 4 to 8 for 3 socket pairs (should this change be covered in socketpair/prj.conf ?)

Even I add this setting, I saw this issue, seems the poll mechanism was broken?

*** Booting Zephyr OS build zephyr-v3.2.0-585-ge80a0c35e666  ***
Alpha: socketpair: 1 <=> 0
Bravo: socketpair: 3 <=> 2
Charlie: socketpair: 5 <=> 4
fd: 1: read 5 bytes
fd: 1: read 5 bytes
fd: 1: read 5 bytes
fd: 1: read 0 bytes
fd: 1: read 0 bytes
fd: 1: read 0 bytes
<keep looping>
fd: 1: read 0 bytes
fd: 1: read 0 bytes
fd: 1: read 0 bytes
fd: 1: read 0 bytes

Please also mention any information which could help others to understand
the problem you're facing:

• What target platform are you using?
• What have you tried to diagnose or workaround this issue?
• Is this a regression? If yes, have you been able to "git bisect" it to a
  specific commit?
• ...

To Reproduce
Steps to reproduce the behavior:

1. mkdir build; cd build
2. cmake -DBOARD=board_xyz
3. make
4. See error

Expected behavior
A clear and concise description of what you expected to happen.

Impact
What impact does this issue have on your progress (e.g., annoyance, showstopper)

Logs and console output
If applicable, add console logs or other types of debug information
e.g Wireshark capture or Logic analyzer capture (upload in zip archive).
copy-and-paste text and put a code fence (```) before and after, to help
explain the issue. (if unable to obtain text log, add a screenshot)

Environment (please complete the following information):

• OS: (e.g. Linux, MacOS, Windows)
• Toolchain (e.g Zephyr SDK, ...)
• Commit SHA or Version used

Additional context
Add any other context that could be relevant to your issue, such as pin setting,
target configuration, ...

[cfriedt]

@rymaj - can you please update the upstream commit in the bug report?

[cfriedt]

It's kind of a PITA to have to jump through all of the hoops and enable a network device just to use socketpair, which really shouldn't require any kind of network interface at all.

Even just trying to run the sample application, I get an error:

west build -p auto -b mps2_an385 -t run samples/net/sockets/socketpair
...
qemu-system-arm: -serial unix:/tmp/slip.sock: Failed to connect to '/tmp/slip.sock': No such file or directory
qemu-system-arm: -serial unix:/tmp/slip.sock: could not connect serial device to character backend 'unix:/tmp/slip.sock'
FAILED: zephyr/CMakeFiles/run_qemu /Users/cfriedt/workspace/zephyrproject/zephyr/build/zephyr/CMakeFiles/run_qemu 
cd /Users/cfriedt/workspace/zephyrproject/zephyr/build && /opt/homebrew/bin/qemu-system-arm -cpu cortex-m3 -machine mps2-an385 -nographic -vgf
ninja: build stopped: subcommand failed.
FATAL ERROR: command exited with status 1: /opt/homebrew/bin/cmake --build /Users/cfriedt/workspace/zephyrproject/zephyr/build --target run

[github-actions]

This issue has been marked as stale because it has been open (more than) 60 days with no activity. Remove the stale label or add a comment saying that you would like to have the label removed otherwise this issue will automatically be closed in 14 days. Note, that you can always re-open a closed issue at any time.

[cfriedt]

Actually, it seems at some point, zephyr_app_main was dropped and we introduced a weak main, but this file was never updated. I'll address that in the same PR as this fix.

[cfriedt]

The output below:

fd: 1: read 0 bytes
fd: 1: read 0 bytes
fd: 1: read 0 bytes
fd: 1: read 0 bytes

Indicates to me that the socket is not operating in blocking mode. However, it was opened in blocking mode (by default), so this is potentially a bug in the sockets implementation.

I'm still working through it though, so will report more information as I find it.