Demonstration that using fallocate() to attempt to allocate more space than the size of the partition does not immediately fail, but instead allocates all free space then fails.


$ ddpt if=/dev/zero of=testimage.ext4 bs=1048576 count=128
128+0 records in
128+0 records out
time to transfer data: 1.885648 secs at 71.18 MB/sec

$ mkfs.ext4 testimage.ext4 
mke2fs 1.41.14 (22-Dec-2010)
testimage.ext4 is not a block special device.
Proceed anyway? (y,n) y
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
Stride=0 blocks, Stripe width=0 blocks
32768 inodes, 131072 blocks
6553 blocks (5.00%) reserved for the super user
First data block=1
Maximum filesystem blocks=67371008
16 block groups
8192 blocks per group, 8192 fragments per group
2048 inodes per group
Superblock backups stored on blocks: 
	8193, 24577, 40961, 57345, 73729

Writing inode tables: done                            
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 36 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.

$ sudo mount -o noatime,loop -t ext4 testimage.ext4 /media/test

$ cd /media/test
ls -l
total 12
drwx------ 2 root root 12288 2012-05-14 12:52 lost+found

$ df | grep test
/dev/loop0              126931      5646    114732   5% /media/test

$ time fallocate -o0 -l999999999 testfile
fallocate: testfile: fallocate failed: No space left on device

real	0m0.002s
user	0m0.000s
sys	0m0.000s

$ df | grep test
/dev/loop0              126931    120378         0 100% /media/test

$ du -B 1 testfile 
117485568	testfile

$ ls -l
total 114744
drwx------ 2 root root     12288 2012-05-14 12:52 lost+found
-rw-r--r-- 1 mark mark 117484544 2012-05-14 12:54 testfile