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fuseloop

A small loopback mount utility using FUSE.

Mainly intended to allow creating of virtual disk images by giving specific offset/size access so that mke2fs can be run on less than the entire file.

Once a virtual disk image has been partitioned and had the filesystems created, "mountlo" can be used to mount them.

Example:

# Create a new file for our disk image (300M in size)
truncate -s 300M mydisk.img

# Use fdisk to create a 100M partition
# If we use 64/32/512 for heads/sectors/sectorsize cylinders=$DISK_SIZE_IN_M
fdisk -c -u -C 300 -H 64 -S 32 -b 512 mydisk.img << EOF
n
p
1

+100M
w
EOF
sectorsize=512

# Use fdisk to give us the correct offset and size values to use with fuseloop
fdisk -c -u -l -C 300 -H 64 -S 32 -b 512 mydisk.img | grep mydisk.img | grep Linux | while read line
do
  set -- $line
  offs=$(($2*$sectorsize))
  size=$((($3-$2)*$sectorsize))
  
  # Random name for partition dev
  part=part.$$
  touch "$part"
  
  # Use fuseloop to expose the partition as an individual file/device
  fuseloop -O "$offs" -S "$size" mydisk.img "$part"
  
  # Create the file system
  mke2fs -F "$part"
  
  # Unmount the partition
  fusermount -u "$part"
  
  # Clean up the partition file we mounted on
  rm -f "$part"
done

# If you want, you can install the SYSLinux MBR to get a bootable image (remember to mark partition 1 as 'active' too!)
dd if=/usr/lib/syslinux/mbr.bin of=mydisk.img conv=notrunc

# With the filesystem laid down on the partition, mountlo can be used to mount it
mountlo -p1 -w mydisk.img /mnt