On Tue, May 06, 2014 at 09:00:54PM +0200, Max Reitz wrote:
The current version of raw-posix always uses ioctl(FS_IOC_FIEMAP) if
FIEMAP is available; lseek with SEEK_HOLE/SEEK_DATA are not even
compiled in in this case. However, there may be implementations which
support the latter but not the former (e.g., NFSv4.2) as well as vice
versa.
To cover both cases, always try SEEK_HOLE/SEEK_DATA (as this will
probably be covered by POSIX soon) and if that does not work, fall back
to FIEMAP; and if that does not work either, treat everything as
allocated.
Btw, while I think that SEEK_HOLE/SEEK_DATA generally is the better API
for qemu, the NFS 4.2 SEEK operation will be sufficient for a proper FIEMAP
implementation, and we'll implement it for the Linux NFS client.