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

[Paul Eggert]

Sunil Mushran wrote:

> SEEK_HOLE/DATA also have the same problem with active files.

Yes, that's true if 'cp' is copying a file while someone else is writing to it.
But the case we're worried about is when 'cp' starts copying a file immediately
after someone else has finished writing to it but data has not been sent to
disk; in that case SEEK_HOLE/DATA should work just as well as the fiemap ioctl.