mount a file system image¶

The following example mounts /tmp/linux.img on /mnt.

start the hypervisor, and run a bash inside the partial virtual machine

$ umvu bash
    

This is the prompt of the partial virtualized shell, let us change it to $$ to show the difference

$ PS1='\$\$ '`
    

let us load vufuse: a user-mode implementation of FUSE (source compatible with FUSE modules)

$$ vu_insmod vufuse
    

nothing is currently mounted on /mnt

$$ ls /mnt
    

the following command mounts the filesystem image /tmp/linux.img

$$ vumount -t vufuseext2 -o ro /tmp/linux.img /mnt
    

now the image has been mounted:

$$ ls /mnt
bin  boot  dev  etc  lib  lost+found  mnt  proc  sbin  tmp  usr
$$ vuumount /mnt
$$ ls /mnt
$$ exit
    

We have left the partial virtual machine

Comments: user can mount any filesystem they like, on any directory. The linux kernel is not involved for all the system calls related to files in the mounted filesystem. The effects of this mount is just perceived by the processes running in the partial virtual machine. vumount is just a wrapper to the mount(1) system call (the command mount(8) does much much more, it is setuid root and requires real uid to be root to permit filesystem mounting (mount(8) works in umvu adding a module of uid/gid virtualization).

create a disk image, partition it, create a filesystem and mount it¶

In this example an 1GiB empty file is seen as a virtual disk, this disk gets partitioned (GPT), an ext4 file system is created on its first partition and finally this file system is mounted on /mnt

start the hypervisor, and run a bash inside the partial virtual machine

$ umvu bash
    

This is the prompt of the partial virtualized shell, let us change it to $$ to show the difference

$ PS1='\$\$ '
    

let us load vudev and vufuse: vudev to virtualize devices and vufuse as in the previous example

$$ vu_insmod vudev vufuse
    

create a 1 GiB large empty file

$$ truncate -s 1G /tmp/disk
$$ ls -l /tmp/disk
-rw-r--r-- 1 renzo renzo 1073741824 Jun  3 11:55 /tmp/disk
    

let us mount the empty file as a partitioned virtual disk:

$$ vumount -t vudevpartx /tmp/disk /dev/hda
Bad MBR signature 0 0
    

clearly if not a partitioned disk, yet. Let us add a partitioning scheme:

$$  /sbin/gdisk /dev/hda
GPT fdisk (gdisk) version 1.0.3
Partition table scan:
MBR: not present
BSD: not present
APM: not present
GPT: not present
Creating new GPT entries.
Command (? for help):  n
Partition number (1-128, default 1):
First sector (34-2097118, default = 2048) or {+-}size{KMGTP}:
Last sector (2048-2097118, default = 2097118) or {+-}size{KMGTP}: +200M
Current type is 'Linux filesystem'
Hex code or GUID (L to show codes, Enter = 8300):
Changed type of partition to 'Linux filesystem'
Command (? for help): n
Partition number (2-128, default 2):
First sector (34-2097118, default = 411648) or {+-}size{KMGTP}:
Last sector (411648-2097118, default = 2097118) or {+-}size{KMGTP}:
Current type is 'Linux filesystem'
Hex code or GUID (L to show codes, Enter = 8300):
Changed type of partition to 'Linux filesystem'
Command (? for help): p
Disk /dev/hda: 2097152 sectors, 1024.0 MiB
Sector size (logical): 512 bytes
Disk identifier (GUID): F2A76123-73ED-4052-BAFE-6B37473E6187
Partition table holds up to 128 entries
Main partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 2097118
Partitions will be aligned on 2048-sector boundaries
Total free space is 2014 sectors (1007.0 KiB)
Number  Start (sector)    End (sector)  Size       Code  Name
1            2048          411647   200.0 MiB   8300  Linux filesystem
2          411648         2097118   823.0 MiB   8300  Linux filesystem
Command (? for help): w
Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!
Do you want to proceed? (Y/N): Y
OK; writing new GUID partition table (GPT) to /dev/hda.
The operation has completed successfully.
The disk has been partitioned:
$$  ls -l /dev/hda1
brw------- 0 renzo renzo 0, 1 Jan  1  1970 /dev/hda1
$$ ls -l /dev/hda2
brw------- 0 renzo renzo 0, 2 Jan  1  1970 /dev/hda2
    

Now it is possible to create an ext4 partition on /dev/hda1

$$ /sbin/mkfs.ext4 /dev/hda1
mke2fs 1.45.1 (12-May-2019)
warning: Unable to get device geometry for /dev/hda1
Creating filesystem with 204800 1k blocks and 51200 inodes
Filesystem UUID: c96c6499-40cd-43df-addf-52e06d7e6842
Superblock backups stored on blocks:


        8193, 24577, 40961, 57345, 73729
Allocating group tables: done
Writing inode tables: done
Creating journal (4096 blocks): done


  Writing superblocks and filesystem accounting information: done
    

now the file system on /dev/hda1 can be mounted on /mnt

$$ vumount -t vufuseext2 -o rw+ /dev/hda1 /mnt
    

add a significative file on /mnt

$$ echo ciao * /mnt/hello
$$ ls -l /mnt
total 13
-rw-r--r-- 1 renzo renzo     5 Jun  3 12:09 hello
drwx------ 2 root  root  12288 Jun  3 12:06 lost+found
$$ vuumount /mnt
$$ vuumount /dev/hda
$$ exit
$
    

mount a user-level networking stack¶

It is possible to provide network partial virtualization using the vunet module

start the hypervisor, and run a bash inside the partial virtual machine

$ umvu bash
    

This is the prompt of the partial virtualized shell, let us change it to $$ to show the difference

$ PS1='\$\$ '
    

let us load vunet

$$ vu_insmod vunet
    

the following command #mounts# a vde network on /dev/net/myvde. (see https://github.com/rd235/vdeplug4)

$$ vumount -t vunetvdestack vxvde:// /dev/net/myvde
    

vustack is the command to select the stack to use.

$$ vustack /dev/net/myvde ip link
1: lo: *LOOPBACK* mtu 65536 qdisc noop state DOWN mode DEFAULT group default qlen 1000


    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: vde0: *BROADCAST,MULTICAST* mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000


    link/ether 7e:76:c0:d7:3b:37 brd ff:ff:ff:ff:ff:ff
    

without vustack I can still access the stack provided by the linux kernel

$$ ip link
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: eth0: *BROADCAST,MULTICAST,UP,LOWER_UP* mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000


    link/ether 80:aa:bb:cc:dd:ee brd ff:ff:ff:ff:ff:ff
    

let us start a bash using /dev/net/myvde as itsdfault net

$$ vustack /dev/net/myvde bash
$ PS1='\$N\$ '
    

let us configure the net

$N$ ip addr add 192.168.250.250/24 dev vde0
$N$ ip link set vde0 up
$N$ ip route add default via 192.168.250.1
$N$ ip addr
1: lo: *LOOPBACK* mtu 65536 qdisc noop state DOWN group default qlen 1000


    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: vde0: *BROADCAST,MULTICAST,UP,LOWER_UP* mtu 1500 qdisc pfifo_fast state UNKNOWN group default qlen 1000


    link/ether 7e:76:c0:d7:3b:37 brd ff:ff:ff:ff:ff:ff


    inet 192.168.250.250/24 scope global vde0


       valid_lft forever preferred_lft forever


    inet6 fe80::7c76:c0ff:fed7:3b37/64 scope link


       valid_lft forever preferred_lft forever
$N$ ip route
default via 192.168.250.1 dev vde0
192.168.250.0/24 dev vde0 proto kernel scope link src 192.168.250.250
$N$ ping 80.80.80.80
PING 80.80.80.80 (80.80.80.80) 56(84) bytes of data.
64 bytes from 80.80.80.80: icmp_seq=1 ttl=52 time=56.9 ms
64 bytes from 80.80.80.80: icmp_seq=2 ttl=52 time=57.9 ms
^C
$N$