[PATCH] Documentation: sandbox.rst: added dhcp network configuration

[Neeraj Pal]

Hello Ahmad,

I have added the DHCP network configuration as discussed
(http://lists.infradead.org/pipermail/barebox/2021-April/035795.html)
Please confirm and let me know if needs any modifications.

Thanks,
Neeraj

diff --git a/Documentation/boards/sandbox.rst b/Documentation/boards/sandbox.rst
index e9e518365..7016312e9 100644
--- a/Documentation/boards/sandbox.rst
+++ b/Documentation/boards/sandbox.rst
@@ -74,3 +74,79 @@ Available sandbox invocation options include:

 To terminate barebox and return to the calling shell, the poweroff command is
 suitable.
+
+Network configuration for Sandbox
+-------------------------------------------------
+
+After running the sanbox, the following steps are required to configure network
+through dhcp.
+Following configuration tested on Ubuntu 20.04 focal LTS
+
+* On host
+
+  * virbr0: virtual bridge interface created by Qemu (easy method)
+
+  * if Qemu virtual bridge (virbr0) is not available then manually
create and configure one bridge like "br0"
+
+    .. code-block:: console
+
+        $ ip link show
+        1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state
UNKNOWN mode DEFAULT group default qlen 1000
+            link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
+        2: enp0s31f6: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500
qdisc fq state DOWN mode DEFAULT group default qlen 1000
+            link/ether xx:xx:xx:xx:xx:xx brd ff:ff:ff:ff:ff:ff
+        3: wlp4s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc
noqueue state UP mode DORMANT group default qlen 1000
+            link/ether xx:xx:xx:xx:xx:xx brd ff:ff:ff:ff:ff:ff
+        4: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc
noqueue state DOWN mode DEFAULT group default qlen 1000
+            link/ether xx:xx:xx:xx:xx:xx brd ff:ff:ff:ff:ff:ff
+        5: virbr0-nic: <BROADCAST,MULTICAST> mtu 1500 qdisc fq master
virbr0 state DOWN mode DEFAULT group default qlen 1000
+            link/ether xx:xx:xx:xx:xx:xx brd ff:ff:ff:ff:ff:ff
+        6: barebox: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state
DOWN mode DEFAULT group default qlen 1000
+            link/ether xx:xx:xx:xx:xx:xx brd ff:ff:ff:ff:ff:ff
+
+    .. code-block:: console
+
+        $ sudo apt install bridge-utils
+        $ sudo ifconfig barebox up
+        $ sudo brctl addif virbr0 barebox
+        $ sudo ip link set barebox master virbr0
+        $ sudo dhclient -v virbr0
+
+* On Sandbox
+
+    .. code-block:: console
+
+        barebox at Sandbox:/ devinfo eth0
+        Parent: tap0
+        Parameters:
+          ethaddr: 00:00:00:00:00:00 (type: MAC)
+          gateway: 0.0.0.0 (type: ipv4)
+          ipaddr: 0.0.0.0 (type: ipv4)
+          linux.bootargs:  (type: string)
+          linux.devname:  (type: string)
+          mode: dhcp (type: enum) (values: "dhcp", "static", "disabled")
+          netmask: 0.0.0.0 (type: ipv4)
+          serverip:  (type: string)
+
+    .. code-block:: console
+
+        barebox at Sandbox:/ dhcp eth0
+        WARNING: eth0: No MAC address set. Using random address
c2:2c:a1:17:b8:47
+        T eth0: DHCP client bound to address 192.168.122.21
+        barebox at Sandbox:/ ping google.com
+        PING google.com (172.217.167.46)
+        host google.com is alive
+
+    .. code-block:: console
+
+        barebox at Sandbox:/ devinfo eth0
+        Parent: tap0
+        Parameters:
+          ethaddr: c2:2c:a1:17:b8:47 (type: MAC)
+          gateway: 192.168.122.1 (type: ipv4)
+          ipaddr: 192.168.122.21 (type: ipv4)
+          linux.bootargs:  (type: string)
+          linux.devname:  (type: string)
+          mode: dhcp (type: enum) (values: "dhcp", "static", "disabled")
+          netmask: 255.255.255.0 (type: ipv4)
+          serverip: 192.168.122.1 (type: string)