| b.liu | e958203 | 2025-04-17 19:18:16 +0800 | [diff] [blame] | 1 | Mounting root file system via SMB (cifs.ko) |
| 2 | =========================================== |
| 3 | |
| 4 | Written 2019 by Paulo Alcantara <palcantara@suse.de> |
| 5 | Written 2019 by Aurelien Aptel <aaptel@suse.com> |
| 6 | |
| 7 | The CONFIG_CIFS_ROOT option enables experimental root file system |
| 8 | support over the SMB protocol via cifs.ko. |
| 9 | |
| 10 | It introduces a new kernel command-line option called 'cifsroot=' |
| 11 | which will tell the kernel to mount the root file system over the |
| 12 | network by utilizing SMB or CIFS protocol. |
| 13 | |
| 14 | In order to mount, the network stack will also need to be set up by |
| 15 | using 'ip=' config option. For more details, see |
| 16 | Documentation/filesystems/nfs/nfsroot.txt. |
| 17 | |
| 18 | A CIFS root mount currently requires the use of SMB1+UNIX Extensions |
| 19 | which is only supported by the Samba server. SMB1 is the older |
| 20 | deprecated version of the protocol but it has been extended to support |
| 21 | POSIX features (See [1]). The equivalent extensions for the newer |
| 22 | recommended version of the protocol (SMB3) have not been fully |
| 23 | implemented yet which means SMB3 doesn't support some required POSIX |
| 24 | file system objects (e.g. block devices, pipes, sockets). |
| 25 | |
| 26 | As a result, a CIFS root will default to SMB1 for now but the version |
| 27 | to use can nonetheless be changed via the 'vers=' mount option. This |
| 28 | default will change once the SMB3 POSIX extensions are fully |
| 29 | implemented. |
| 30 | |
| 31 | Server configuration |
| 32 | ==================== |
| 33 | |
| 34 | To enable SMB1+UNIX extensions you will need to set these global |
| 35 | settings in Samba smb.conf: |
| 36 | |
| 37 | [global] |
| 38 | server min protocol = NT1 |
| 39 | unix extension = yes # default |
| 40 | |
| 41 | Kernel command line |
| 42 | =================== |
| 43 | |
| 44 | root=/dev/cifs |
| 45 | |
| 46 | This is just a virtual device that basically tells the kernel to mount |
| 47 | the root file system via SMB protocol. |
| 48 | |
| 49 | cifsroot=//<server-ip>/<share>[,options] |
| 50 | |
| 51 | Enables the kernel to mount the root file system via SMB that are |
| 52 | located in the <server-ip> and <share> specified in this option. |
| 53 | |
| 54 | The default mount options are set in fs/cifs/cifsroot.c. |
| 55 | |
| 56 | server-ip |
| 57 | IPv4 address of the server. |
| 58 | |
| 59 | share |
| 60 | Path to SMB share (rootfs). |
| 61 | |
| 62 | options |
| 63 | Optional mount options. For more information, see mount.cifs(8). |
| 64 | |
| 65 | Examples |
| 66 | ======== |
| 67 | |
| 68 | Export root file system as a Samba share in smb.conf file. |
| 69 | |
| 70 | ... |
| 71 | [linux] |
| 72 | path = /path/to/rootfs |
| 73 | read only = no |
| 74 | guest ok = yes |
| 75 | force user = root |
| 76 | force group = root |
| 77 | browseable = yes |
| 78 | writeable = yes |
| 79 | admin users = root |
| 80 | public = yes |
| 81 | create mask = 0777 |
| 82 | directory mask = 0777 |
| 83 | ... |
| 84 | |
| 85 | Restart smb service. |
| 86 | |
| 87 | # systemctl restart smb |
| 88 | |
| 89 | Test it under QEMU on a kernel built with CONFIG_CIFS_ROOT and |
| 90 | CONFIG_IP_PNP options enabled. |
| 91 | |
| 92 | # qemu-system-x86_64 -enable-kvm -cpu host -m 1024 \ |
| 93 | -kernel /path/to/linux/arch/x86/boot/bzImage -nographic \ |
| 94 | -append "root=/dev/cifs rw ip=dhcp cifsroot=//10.0.2.2/linux,username=foo,password=bar console=ttyS0 3" |
| 95 | |
| 96 | |
| 97 | 1: https://wiki.samba.org/index.php/UNIX_Extensions |