bug#6131: [PATCH]: fiemap support for efficient sparse file copy

[Paul Eggert]

On 06/10/2010 05:35 PM, Tao Ma wrote:

> there is a flag FIEMAP_EXTENT_DELALLOC in fiemap ...
> with dd if=/dev/zero of=/mnt/ext4/a bs=1M count=1 seek=1
> the ext4 can't return a valid fiemap extent. 

Hmm, this sounds like a fairly serious bug, in that it would prevent this
part of cp from working.  What does the fiemap ioctl return in this buggy case?
Is there some way that cp can detect the bug, and report it to the user,
or work around it?  Or should we just assume that the bug will get fixed
and that cp shouldn't worry about it?