bug#14618: Erroneous sparse copy command results in empty file

[Pádraig Brady]

On 06/14/2013 12:35 PM, Koen De Wit wrote:
> When trying to create a sparse copy of a file on a different filesystem you 
> get an "Invalid cross-device link" error, as expected. However, an empty file 
> is created instead of the sparse copy:

As a side note, sparse copying is a separate thing to reflinking.

> # mkfs.btrfs -f /dev/sde1
> # mkfs.btrfs -f /dev/sde2
> # mount /dev/sde1 /mnt/part1
> # mount /dev/sde2 /mnt/part2
> # echo "abc" > /mnt/part1/testfile
> # ./cp --reflink /mnt/part1/testfile /mnt/part2/testcopy
> ./cp: failed to clone ‘/mnt/part2/testcopy’ from ‘/mnt/part1/testfile’: 
> Invalid cross-device link
> # ls -la /mnt/part1/testfile
> -rw-r--r--. 1 root root 4 Jun 14 14:49 /mnt/part1/testfile
> # ls -la /mnt/part2/testcopy
> -rw-r--r--. 1 root root 0 Jun 14 14:49 /mnt/part2/testcopy
> 
> The same occurs when trying to create a sparse copy on a filesystem that does 
> not support sparse copies:
> 
> # mkfs.ext3 /dev/sde1
> # mount /dev/sde1 /mnt/part1
> # echo "abc" > /mnt/part1/testfile
> # ./cp --reflink /mnt/part1/testfile /mnt/part1/testcopy
> ./cp: failed to clone ‘/mnt/part1/testcopy’ from ‘/mnt/part1/testfile’: 
> Inappropriate ioctl for device
> # ls -la /mnt/part1
> (...)
> -rw-r--r--. 1 root root 0 Jun 14 14:58 testcopy
> -rw-r--r--. 1 root root 4 Jun 14 14:58 testfile
> 
> If creating a sparse copy fails, no file should be created.
> 
> ln treats this error in the right way:
> 
> # ln /mnt/part1/testfile /mnt/part2/testlink
> ln: creating hard link `/mnt/part2/testlink' => `/mnt/part1/testfile': 
> Invalid cross-device link
> # ls -la /mnt/part2/testlink
> ls: cannot access /mnt/part2/testlink: No such file or directory
> 
> Tested with coreutils today's git HEAD and kernel 3.9.5.

This was discussed previously:
http://lists.gnu.org/archive/html/coreutils/2013-03/msg00056.html
Summary of that is that it may be best handled outside of cp.

cheers,
Pádraig.