Messages in this thread |  | | | Date | Wed, 09 Jul 2003 17:43:33 -0400 | | From | Jeff Garzik <> | | Subject | Re: ->direct_IO API change in current 2.4 BK |
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Trond Myklebust wrote: >>>>>>" " == Jeff Garzik <jgarzik@pobox.com> 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.
You misunderstand. The 2.4.15 direct_IO hook was _not_ conditionally defined. It appeared in the middle of a stable series, yes. It has a feature macro, yes. But the definition of the hook in include/linux/fs.h does not _change_ based on a define. That is what I mean by a conditional hook definition.
It is far less trouble for everyone to add a new hook, instead of changing an existing hook, in the middle of a stable series.
> 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...
No doubt you can find more :) That doesn't make the right thing to do, though :)
> 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...
We cannot just-fix-up filesystems which are not in-tree, which is what the KERNEL_HAS_O_DIRECT2 define would be mainly used for. In-tree filesystems would just unconditionally use the new, or old, interface as they chose.
> The problem with read_inode2() was rather that it overloaded the the > existing iget4() interface...
The higher-level problem was that we didn't want to change the VFS API... otherwise we could have simply used the new interface, and converted all in-tree filesystems.
Jeff
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