... otherwise zfs_getpages would mostly be called with one page at a time.
It is expected that ZFS VOP_BMAP is only called from vnode_pager_haspage.
Since ZFS files can have variable block sizes and also because we don't
really know if any given blocks are consecutive, we can not really report
any additional blocks behind or ahead of a given block. Since physical
block numbers do not make sense for ZFS, we do not do any real translation
and thus pass back blk = lblk. The net effect is that vnode_pager_haspage
knows that the block exists and that the pages backed by the block can be
accessed. vnode_pager_haspage may be wrong about the exact count of the
pages backed by the block, because of a variable block size, which
vnode_pager_haspage doesn't really know - it only knows max block size in
a filesystem. So pages from multiple blocks can be passed to zfs_getpages,
but that is expected and correctly handled.
vnode_pager should not call zfs_bmap for any other reason, because ZFS
implements VOP_PUTPAGES and thus vnode_pager_generic_getpages is not used.
vfs_cluster code vfs_bio code should not be called for ZFS, because ZFS does
not use buffer cache layer.
Also, ZFS does not use vn_bmap_seekhole, it has its prviate mechanism for
working with holes.
The above list should cover all the current calls to VOP_BMAP.
Reviewed by: kib
MFC after: 6 weeks
7192f62bcc