RFC: SEEK_HOLE/SEEK_DATA common implementation

[mdf at FreeBSD.org]

On Thu, Mar 29, 2012 at 2:34 AM, Konstantin Belousov
<kostikbel at gmail.com> wrote:
> Filesystem probably should always fall back to calling vop_stdioctl()
> manually if it ever implements VOP_IOCTL, regardless of seek_hole/data.

We can't if there's a use of VOP_BMAP() in one of the ioctls.  For
OneFS, a call to VOP_BMAP is fatal.  That operation doesn't work with
our system.

We could implement SEEK_HOLE/SEEK_DATA semi-efficiently, but
implementing a custom filesystem becomes very complex once one has not
only to manage replacing all VOPs where the default doesn't work but
also has to know there's a bunch of ioctls in VOP_IOCTL that must be
handled as well.

Thanks,
matthew