Rework the syscall interposition architecture so FreeRTOS works
standalone (without VFS) and VFS optionally overrides with strong
symbols. All kernel FDs are registered with VFS via
esp_vfs_register_fd_with_local_fd, so the application only sees
VFS-allocated FD numbers, preventing numerical collisions between
kernel FDs and VFS-internal FD slots.
FreeRTOS side:
- Create linux_port_coop_internal.h with LINUX_COOP_IO_LOOP,
LINUX_COOP_RESOLVE, linux_coop_yield and FD state table functions
- Export cooperative I/O primitives (freertos_linux_coop_read/write/
open/close/fcntl/select/pread/pwrite/readv/writev/recv/send/
recvfrom/sendto/recvmsg/sendmsg/connect/accept/pselect/poll/
socket/socketpair/pipe/pipe2/dup/dup2/syscalls_init)
- Define weak POSIX symbols calling through to the cooperative
primitives; keep nanosleep/sleep/usleep as strong (not FD-related)
- Refactor freertos_linux_coop_syscalls.h into a pure public API header
VFS side:
- Register the Linux host FS with esp_vfs_register_fs_with_id() as a
proper VFS driver; register stdin/stdout/stderr at init (priority 99)
- Rewrite vfs_linux.c with strong POSIX symbols dispatching through
esp_vfs_*
- Add strong overrides for FD-creating syscalls (open, pipe, pipe2,
socket, socketpair, dup, dup2, accept) that register returned FDs
with VFS
- Add strong overrides for FD-translating syscalls (readv, writev,
recv, send, recvfrom, sendto, recvmsg, sendmsg, connect, pselect,
poll) that translate VFS FD to kernel FD
- Delete vfs_coop_syscalls.c (absorbed into FreeRTOS weak + VFS strong)
- Update CMakeLists.txt: remove vfs_coop_syscalls.c, add linker hook
