riscv64: Improve command forwarding

Previous implementation uses `netcat` to test existence of
pre-configured target port, but that port is occupied in advance of
`sshd` inside VM is ready.

Replace `netcat` with `ssh` with `ConnectTimeout` set to directly verify
the connectivity of `sshd`.

Signed-off-by: Ruoqing He <[email protected]>

riscv64/build_finalize.sh

@@ -5,7 +5,7 @@ apt-get update
 
 DEBIAN_FRONTEND="noninteractive" apt-get install --no-install-recommends -y \
     openssh-client libslirp-dev libfdt-dev libglib2.0-dev libssl-dev \
-    libpixman-1-dev netcat
+    libpixman-1-dev
 
 # Modify fstab to mount `tmpfs` during boot
 # See: https://wiki.qemu.org/Documentation/9p_root_fs#Let's_start_the_Installation

riscv64/start_in_qemu.sh

@@ -29,11 +29,12 @@ cp -a $WORKDIR $ROOTFS_DIR/root
 
 HOST=riscv-qemu
 
-while ! nc -z localhost 2222; do   
-  echo "Dialing qemu-system-riscv64..."
-  sleep 1
+echo "Testing SSH connectivity to $HOST..."
+while ! ssh -o ConnectTimeout=3 $HOST exit; do
+  echo "$HOST is not ready..."
 done
 
 # Issue command
 COMMAND=$@
+echo "$HOST is ready, forwarding command: $COMMAND"
 ssh $HOST "export PATH=\"\$PATH:/root/.cargo/bin\" && cd workdir && $COMMAND"