boards/esp32c3-devkit: add Dropbear SSH server configuration

Documentation/platforms/risc-v/esp32c3/boards/esp32c3-devkit/index.rst

@@ -211,6 +211,54 @@ should look like this::
     hmac sha256 success
     hmac sha256 success
 
+dropbear
+--------
+
+This configuration brings up the `Dropbear <https://matt.ucc.asn.au/dropbear/dropbear.html>`__
+SSH server so that an NSH session can be reached over the network. It pulls in
+Wi-Fi station mode, the DHCP client, the WAPI tooling and ``/dev/urandom`` so the
+link is configured automatically at boot, and it persists the SSH host key and
+the user database on the SPIFFS partition mounted at ``/data``.
+
+The Wi-Fi credentials shipped in the defconfig are placeholders. Set your own
+SSID and passphrase before flashing::
+
+    $ make menuconfig
+    -> Application Configuration
+        -> Network Utilities
+            -> Network initialization (NETUTILS_NETINIT [=y])
+                -> WAPI Configuration
+
+
+When the board boots it joins the configured network, requests an address over
+DHCP and starts the Dropbear daemon. Check the assigned address with::
+
+    nsh> ifconfig
+    wlan0   Link encap:Ethernet HWaddr 84:f7:03:xx:xx:xx at RUNNING mtu 1504
+            inet addr:192.168.1.xx DRaddr:192.168.1.x Mask:255.255.255.0
+
+The first time the daemon runs it generates an ECDSA host key and stores it at
+``/data/dropbear_ecdsa_host_key`` (``CONFIG_NETUTILS_DROPBEAR_HOSTKEY_PATH``), and
+the user accounts are read from ``/data/passwd`` (``CONFIG_FSUTILS_PASSWD_PATH``).
+Because both files live on the persistent ``/data`` partition, the host key and
+the credentials survive reboots, so clients do not see a changing host key.
+
+Add a user from the board before connecting (the password file is created on the
+first ``useradd``)::
+
+    nsh> useradd admin mypassword
+
+From a host on the same network, open an SSH session and run NSH commands
+remotely::
+
+    $ ssh admin@192.168.1.xx
+    admin@192.168.1.xx's password:
+    nsh>
+
+Each session runs over a pseudo-terminal (``CONFIG_PSEUDOTERM``), and ``Ctrl-C``
+is forwarded to the remote NSH (``CONFIG_TTY_SIGINT``). The daemon keeps running
+after a session ends, so multiple clients can connect over time.
+
 efuse
 -----
 

boards/risc-v/esp32c3/esp32c3-devkit/configs/dropbear/defconfig

@@ -0,0 +1,93 @@
+#
+# This file is autogenerated: PLEASE DO NOT EDIT IT.
+#
+# You can use "make menuconfig" to make any modifications to the installed .config file.
+# You can then do "make savedefconfig" to generate a new defconfig file that includes your
+# modifications.
+#
+# CONFIG_NDEBUG is not set
+# CONFIG_NSH_ARGCAT is not set
+# CONFIG_NSH_CMDOPT_HEXDUMP is not set
+CONFIG_ALLOW_BSD_COMPONENTS=y
+CONFIG_ARCH="risc-v"
+CONFIG_ARCH_BOARD="esp32c3-devkit"
+CONFIG_ARCH_BOARD_COMMON=y
+CONFIG_ARCH_BOARD_ESP32C3_DEVKIT=y
+CONFIG_ARCH_CHIP="esp32c3"
+CONFIG_ARCH_CHIP_ESP32C3=y
+CONFIG_ARCH_INTERRUPTSTACK=2048
+CONFIG_ARCH_IRQ_TO_NDX=y
+CONFIG_ARCH_MINIMAL_VECTORTABLE_DYNAMIC=y
+CONFIG_ARCH_NUSER_INTERRUPTS=17
+CONFIG_ARCH_RISCV=y
+CONFIG_ARCH_STACKDUMP=y
+CONFIG_BOARD_LOOPSPERMSEC=15000
+CONFIG_BUILTIN=y
+CONFIG_DEV_URANDOM=y
+CONFIG_DRIVERS_IEEE80211=y
+CONFIG_DRIVERS_WIRELESS=y
+CONFIG_ESPRESSIF_SPIFLASH=y
+CONFIG_ESPRESSIF_SPIFLASH_SPIFFS=y
+CONFIG_ESPRESSIF_WIFI=y
+CONFIG_EXAMPLES_RANDOM=y
+CONFIG_FSUTILS_PASSWD=y
+CONFIG_FSUTILS_PASSWD_PATH="/data/passwd"
+CONFIG_FS_PROCFS=y
+CONFIG_IDLETHREAD_STACKSIZE=2048
+CONFIG_INIT_ENTRYPOINT="nsh_main"
+CONFIG_INIT_STACKSIZE=8192
+CONFIG_INTELHEX_BINARY=y
+CONFIG_IOB_BUFSIZE=128
+CONFIG_IOB_NBUFFERS=160
+CONFIG_IOB_THROTTLE=24
+CONFIG_LIBC_GAISTRERROR=y
+CONFIG_LIBC_PERROR_STDOUT=y
+CONFIG_LIBC_STRERROR=y
+CONFIG_NETDB_DNSCLIENT=y
+CONFIG_NETDEV_LATEINIT=y
+CONFIG_NETDEV_PHY_IOCTL=y
+CONFIG_NETDEV_WIRELESS_IOCTL=y
+CONFIG_NETINIT_DHCPC=y
+CONFIG_NETINIT_WAPI_PASSPHRASE="mypasswd"
+CONFIG_NETINIT_WAPI_SSID="myssid"
+CONFIG_NETUTILS_DROPBEAR=y
+CONFIG_NETUTILS_DROPBEAR_HOSTKEY_PATH="/data/dropbear_ecdsa_host_key"
+CONFIG_NETUTILS_IPERF=y
+CONFIG_NET_BROADCAST=y
+CONFIG_NET_ETH_PKTSIZE=1514
+CONFIG_NET_ICMP_SOCKET=y
+CONFIG_NET_TCP=y
+CONFIG_NET_TCP_DELAYED_ACK=y
+CONFIG_NET_TCP_WRITE_BUFFERS=y
+CONFIG_NET_UDP=y
+CONFIG_NFILE_DESCRIPTORS_PER_BLOCK=6
+CONFIG_NSH_BUILTIN_APPS=y
+CONFIG_NSH_DROPBEAR=y
+CONFIG_NSH_FILEIOSIZE=512
+CONFIG_NSH_READLINE=y
+CONFIG_NSH_STRERROR=y
+CONFIG_PREALLOC_TIMERS=0
+CONFIG_PSEUDOTERM=y
+CONFIG_PSEUDOTERM_RXBUFSIZE=1024
+CONFIG_PSEUDOTERM_TXBUFSIZE=2048
+CONFIG_PTHREAD_MUTEX_TYPES=y
+CONFIG_RR_INTERVAL=200
+CONFIG_SCHED_BACKTRACE=y
+CONFIG_SCHED_LPWORK=y
+CONFIG_SCHED_WAITPID=y
+CONFIG_SIG_DEFAULT=y
+CONFIG_START_DAY=29
+CONFIG_START_MONTH=11
+CONFIG_START_YEAR=2019
+CONFIG_SYSTEM_DHCPC_RENEW=y
+CONFIG_SYSTEM_DUMPSTACK=y
+CONFIG_SYSTEM_NSH=y
+CONFIG_SYSTEM_PING=y
+CONFIG_TESTING_GETPRIME=y
+CONFIG_TESTING_OSTEST=y
+CONFIG_TLS_TASK_NELEM=4
+CONFIG_TTY_SIGINT=y
+CONFIG_UART0_SERIAL_CONSOLE=y
+CONFIG_WIRELESS=y
+CONFIG_WIRELESS_WAPI=y
+CONFIG_WIRELESS_WAPI_CMDTOOL=y