Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 105 insertions, 0 deletions

diff --git a/Documentation/filesystems/cifs/cifsroot.rst b/Documentation/filesystems/cifs/cifsroot.rst
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+.. SPDX-License-Identifier: GPL-2.0
+
+===========================================
+Mounting root file system via SMB (cifs.ko)
+===========================================
+
+Written 2019 by Paulo Alcantara <palcantara@suse.de>
+
+Written 2019 by Aurelien Aptel <aaptel@suse.com>
+
+The CONFIG_CIFS_ROOT option enables experimental root file system
+support over the SMB protocol via cifs.ko.
+
+It introduces a new kernel command-line option called 'cifsroot='
+which will tell the kernel to mount the root file system over the
+network by utilizing SMB or CIFS protocol.
+
+In order to mount, the network stack will also need to be set up by
+using 'ip=' config option. For more details, see
+Documentation/admin-guide/nfs/nfsroot.rst.
+
+A CIFS root mount currently requires the use of SMB1+UNIX Extensions
+which is only supported by the Samba server. SMB1 is the older
+deprecated version of the protocol but it has been extended to support
+POSIX features (See [1]). The equivalent extensions for the newer
+recommended version of the protocol (SMB3) have not been fully
+implemented yet which means SMB3 doesn't support some required POSIX
+file system objects (e.g. block devices, pipes, sockets).
+
+As a result, a CIFS root will default to SMB1 for now but the version
+to use can nonetheless be changed via the 'vers=' mount option.  This
+default will change once the SMB3 POSIX extensions are fully
+implemented.
+
+Server configuration
+====================
+
+To enable SMB1+UNIX extensions you will need to set these global
+settings in Samba smb.conf::
+
+    [global]
+    server min protocol = NT1
+    unix extension = yes        # default
+
+Kernel command line
+===================
+
+::
+
+    root=/dev/cifs
+
+This is just a virtual device that basically tells the kernel to mount
+the root file system via SMB protocol.
+
+::
+
+    cifsroot=//<server-ip>/<share>[,options]
+
+Enables the kernel to mount the root file system via SMB that are
+located in the <server-ip> and <share> specified in this option.
+
+The default mount options are set in fs/cifs/cifsroot.c.
+
+server-ip
+	IPv4 address of the server.
+
+share
+	Path to SMB share (rootfs).
+
+options
+	Optional mount options. For more information, see mount.cifs(8).
+
+Examples
+========
+
+Export root file system as a Samba share in smb.conf file::
+
+    ...
+    [linux]
+	    path = /path/to/rootfs
+	    read only = no
+	    guest ok = yes
+	    force user = root
+	    force group = root
+	    browseable = yes
+	    writeable = yes
+	    admin users = root
+	    public = yes
+	    create mask = 0777
+	    directory mask = 0777
+    ...
+
+Restart smb service::
+
+    # systemctl restart smb
+
+Test it under QEMU on a kernel built with CONFIG_CIFS_ROOT and
+CONFIG_IP_PNP options enabled::
+
+    # qemu-system-x86_64 -enable-kvm -cpu host -m 1024 \
+    -kernel /path/to/linux/arch/x86/boot/bzImage -nographic \
+    -append "root=/dev/cifs rw ip=dhcp cifsroot=//10.0.2.2/linux,username=foo,password=bar console=ttyS0 3"
+
+
+1: https://wiki.samba.org/index.php/UNIX_Extensions