clean up the dabuf mappedbno interface v2

Christoph Hellwig
2019-11-20T11:17:29Z

Hi all,

this (lightly tested) series cleanups the strange mappedbno argument
to various dabuf helpers. If that argument has a positive value
it is used as xfs_daddr_t to get/read the block, and otherwise
it is overloaded for a flag. This series splits out the users that
have a xfs_daddr_t to just use the buffer interfaces directly, and
the replaces the magic with a flags argument and one properly
named flag.

Changes since v1:
- return *nmaps = 0 for holes from xfs_dabuf_map
- add a new patch to refactor xfs_dabuf_map