arch/sim: set stdin/stdout nonblocking in host_uart_start()

When NuttX sim is connected via pipe (e.g. by an automation tool),
if the host side does not read stdout in time, the pipe buffer fills
up and write(1, ...) blocks the entire sim process. This happens
inside host_uninterruptible (irq disabled), so the NuttX scheduler
is completely frozen and all threads stop.

Set both stdin and stdout to nonblocking via ioctl(FIONBIO) so that
read()/write() return EAGAIN instead of blocking. The TX data stays
in the NuttX xmit buffer and sim_tty_work retries every 1ms until
the pipe has space.

Signed-off-by: chenzihan1 <chenzihan1@xiaomi.com>
Signed-off-by: ligd <liguangdi1@xiaomi.com>
Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

Author: xiaoxiang781216

arch/sim/src/sim/posix/sim_hostuart.c

@@ -26,6 +26,7 @@
 
 #include <sys/ioctl.h>
 #include <fcntl.h>
+#include <sys/ioctl.h>
 #include <stdbool.h>
 #include <unistd.h>
 #include <string.h>
@@ -95,6 +96,8 @@ static void restoremode(void)
 
 void host_uart_start(void)
 {
+  int nonblock = 1;
+
   /* Get the current stdin terminal mode */
 
   tcgetattr(0, &g_cooked);
@@ -103,6 +106,14 @@ void host_uart_start(void)
 
   setrawmode(0);
 
+  host_uninterruptible_no_return(ioctl, 0, FIONBIO, &nonblock);
+
+  /* Set stdout to non-blocking to prevent write(1, ...) from blocking
+   * the entire sim process when the host pipe buffer is full.
+   */
+
+  host_uninterruptible_no_return(ioctl, 1, FIONBIO, &nonblock);
+
   /* Restore the original terminal mode before exit */
 
   atexit(restoremode);