Simple single-file FUSE implementation of copy-on-write using sparse files as storage to copyup

Example session:

mount | grep "on / "

/dev/sda8 on / type reiserfs (rw,user_xattr,usrquota,acl)

touch mountpoint_file

./fusecow /dev/sda8 mountpoint_file write_file

reiserfsck mountpoint_file

Replaying journal: Trans replayed: mountid 636, transid 14679519, desc 901, len 2, commit 904, next trans offset 887 Trans replayed: mountid 636, transid 14679520, desc 905, len 1, commit 907, next trans offset 890 ...

ls -lh

-rw------- 1 root disk 30G Jan 22 17:01 mountpoint_file -rwxr-xr-x 1 root root 29G Jan 23 06:01 write_file -rwxr-xr-x 1 root root 472K Jan 23 06:01 write_file.map

du -sh *

32M mountpoint_file 31M write_file 281K write_file.map

mkdir mnt && mount -o loop mountpoint_file mnt

dd if=/dev/urandom of=mnt/usr/local/etc/qqqqq bs=1M count=32

umount mnt

fusermount -u mountpoint_file

du -sh *

0 mountpoint_file 65M write_file 289K write_file.map

ls /usr/local/etc/qqqqq

ls: cannot access /usr/local/etc/qqqqq: No such file or directory

./fusecow /dev/sda8 mountpoint_file write_file

mount -o loop mountpoint_file mnt

ls -lh mnt/usr/local/etc/qqqqq

-rw-r--r-- 1 root root 32M Jan 23 06:05 mnt/usr/local/etc/qqqqq

Limitations:

1. Slow
2. Cannot grow files yet
3. Unstable