Re: ->direct_IO API change in current 2.4 BK

[Trond Myklebust]

>>>>> " " == Jeff Garzik <[e-mail]> writes:

     > Having the stable API change, conditional on a define, is
     > really nasty and IMO will create maintenance and support
     > headaches down the line.  I do not recall Linux VFS _ever_
     > having a hook's definition conditional.  We should not start
     > now...

direct_IO() was precisely such a conditional hook definition. It
appeared in 2.4.15, and anybody who does not check for
KERNEL_HAS_O_DIRECT is not backward compatible.

To comment further: There is at least one example I can think of which
was exactly equivalent to the proposed change, namely the redefinition
of the filldir_t type in 2.4.9. It was admittedly not documented using
a define...

Note: We could at the same time replace the name direct_IO() with
direct_IO2() (that has several precedents).  There are currently only
a small number of filesystems that provide O_DIRECT, and converting
them all is (as has been pointed out before) trivial...

The problem with read_inode2() was rather that it overloaded the the
existing iget4() interface...

Cheers,
  Trond