miguel@Atalaya:~$ cd /dev/loop
loop/  loop0  loop1  loop2  loop3  loop4  loop5  loop6  loop7
miguel@Atalaya:~$ cd /dev/loop/
miguel@Atalaya:/dev/loop$ sudo dd if=/dev/zero of=carlosloop bs=1k count=$((1024*100))
Password:
102400+0 registros leídos
102400+0 registros escritos
104857600 bytes transferred in 1,000918 seconds (104761428 bytes/sec)
miguel@Atalaya:/dev/loop$ ls
0  carlosloop
miguel@Atalaya:/dev/loop$ sudo mkfs.reiserfs -f carlosloop
mkfs.reiserfs 3.6.19 (2003 www.namesys.com)

A pair of credits:
Edward Shushkin wrote the encryption and compression  file plugins,  and the V3
journal relocation code.

Vitaly Fertman wrote  fsck for V3 and  maintains the reiserfsprogs package now.
He wrote librepair,  userspace plugins repair code, fsck for V4,  and worked on
developing libreiser4 and userspace plugins with Umka.


carlosloop is not a block special device
Continue (y/n):y
Guessing about desired format.. Kernel 2.6.12-10-386 is running.
Format 3.6 with standard journal
Count of blocks on the device: 25600
Number of blocks consumed by mkreiserfs formatting process: 8212
Blocksize: 4096
Hash function used to sort names: "r5"
Journal Size 8193 blocks (first block 18)
Journal Max transaction length 1024
inode generation number: 0
UUID: f23ae112-cebd-4042-aa4f-992fbddef7cc
Initializing journal - 0%....20%....40%....60%....80%....100%
Syncing..ok

Tell your friends to use a kernel based on 2.4.18 or later, and especially not a
kernel based on 2.4.9, when you use reiserFS. Have fun.

ReiserFS is successfully created on carlosloop.
miguel@Atalaya:/dev/loop$ mkdir /tmp/prueba
miguel@Atalaya:/dev/loop$ sudo mount -o loop,rw /dev/loop/carlosloop /tmp/prueba/
miguel@Atalaya:/dev/loop$ sudo chmod 775 /tmp/prueba/
miguel@Atalaya:/dev/loop$ df -h
S.ficheros            Tamaño Usado  Disp Uso% Montado en
/dev/hda6             3,9G  3,5G  236M  94% /
tmpfs                 252M     0  252M   0% /dev/shm
tmpfs                 252M   13M  240M   5% /lib/modules/2.6.12-10-386/volatile
/dev/hda7              15G  863M   13G   7% /media/hda7
/dev/hda1              56G   18G   38G  33% /media/windows
/dev/loop/carlosloop  100M   33M   68M  33% /tmp/prueba
miguel@Atalaya:/dev/loop$ cd /tmp/prueba/
miguel@Atalaya:/tmp/prueba$ sudo dd if=/dev/zero of=desbordamiento bs=1k count=$((1024*69))
dd: escribiendo «desbordamiento»: No queda espacio en el dispositivo
69481+0 registros leídos
69480+0 registros escritos
71147520 bytes transferred in 1,292817 seconds (55032935 bytes/sec)
miguel@Atalaya:/tmp/prueba$ umount /dev/loop/carlosloop
umount: /dev/loop/carlosloop no está en fstab (y usted no es el usuario root)

# Los comandos de montaje y desmontaje deben correrse como root

miguel@Atalaya:/tmp/prueba$ sudo umount /dev/loop/carlosloop
umount: /tmp/prueba: dispositivo ocupado
umount: /tmp/prueba: dispositivo ocupado

# No se puede desmontar la partición si me encuentro dentro de ella

miguel@Atalaya:/tmp/prueba$ cd ~
miguel@Atalaya:~$ sudo umount /dev/loop/carlosloop